The vicarious learning pathway to fear 40 years on

Clinical Psychology Review 28 (2008) 1249–1265

Contents lists available at ScienceDirect

Clinical Psychology Review

The vicarious learning pathway to fear 40 years on Chris Askew 1, Andy P. Field ⁎ Department of Psychology, University of Sussex, Falmer, Brighton, East Sussex, BN1 9QH, UK

a r t i c l e

i n f o

Article history: Received 24 September 2007 Received in revised form 3 May 2008 Accepted 8 May 2008 Keywords: Fear Anxiety Vicarious learning

a b s t r a c t Forty years on from the initial idea that fears could be learnt vicariously through observing other people's responses to a situation or stimulus, this review looks at the evidence for this theory as an explanatory model of clinical fear. First, we review early experimental evidence that fears can be learnt vicariously before turning to the evidence from both primate and human research that clinical fears can be acquired in this way. Finally, we review recent evidence from research on non-anxious children. Throughout the review we highlight problems and areas for future research. We conclude by exploring the likely underlying mechanisms in the vicarious learning of fear and the resulting clinical implications. Crown Copyright © 2008 Published by Elsevier Ltd. All rights reserved.

Contents 1. 2.

3.

Introduction . . . . . . . . . . . . . . . . . . . . . . . . Early evidence for vicarious learning as a pathway to fear . . 2.1. Experimental studies with adults. . . . . . . . . . . 2.2. Interpretation of the model's experience and response 2.3. The nature of the CS and US . . . . . . . . . . . . . 2.4. Measurement of the fear response . . . . . . . . . . 2.5. Limitations . . . . . . . . . . . . . . . . . . . . . Retrospective self-report in already anxious humans . . . . .

3.1. The Phobic Origin Questionnaire . . . . . . . . . . 3.2. Structured interview and other questionnaires . . . 3.3. Limitations of the self-report literature . . . . . . . 4. Monkey business . . . . . . . . . . . . . . . . . . . . 4.1. Can monkeys acquire fears observationally? . . . . 4.2. Exploring the mechanism of learning . . . . . . . 4.3. Clinical implications from work using monkeys . . . 5. Research in non-anxious children . . . . . . . . . . . . . 5.1. Social referencing and vicarious learning with infants 5.2. Vicarious learning in children . . . . . . . . . . . 6. Theoretical and clinical implications . . . . . . . . . . . 6.1. The mechanisms of vicarious learning . . . . . . . 6.2. Implications for prevention and treatment . . . . . 7. Summary . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . .

. . . . . . . .

. . . . . . . .

. . . . . . . .

. . . . . . . .

. . . . . . . .

. . . . . . . .

. . . . . . . .

. . . . . . . .

. . . . . . . .

. . . . . . . .

. . . . . . . .

. . . . . . . .

. . . . . . . .

. . . . . . . .

. . . . . . . .

. . . . . . . .

. . . . . . . .

. . . . . . . .

. . . . . . . .

. . . . . . . .

. . . . . . . .

. . . . . . . .

. . . . . . . .

. . . . . . . .

. . . . . . . .

. . . . . . . .

. . . . . . . .

. . . . . . . .

. . . . . . . .

. . . . . . . .

1250 1250 1250 1251 1252 1253 1253 1254

. . . . . . . . . . . . . . .

. . . . . . . . . . . . . . .

. . . . . . . . . . . . . . .

. . . . . . . . . . . . . . .

. . . . . . . . . . . . . . .

. . . . . . . . . . . . . . .

. . . . . . . . . . . . . . .

. . . . . . . . . . . . . . .

. . . . . . . . . . . . . . .

. . . . . . . . . . . . . . .

. . . . . . . . . . . . . . .

. . . . . . . . . . . . . . .

. . . . . . . . . . . . . . .

. . . . . . . . . . . . . . .

. . . . . . . . . . . . . . .

. . . . . . . . . . . . . . .

. . . . . . . . . . . . . . .

. . . . . . . . . . . . . . .

. . . . . . . . . . . . . . .

. . . . . . . . . . . . . . .

. . . . . . . . . . . . . . .

. . . . . . . . . . . . . . .

. . . . . . . . . . . . . . .

. . . . . . . . . . . . . . .

. . . . . . . . . . . . . . .

. . . . . . . . . . . . . . .

. . . . . . . . . . . . . . .

. . . . . . . . . . . . . . .

. . . . . . . . . . . . . . .

. . . . . . . . . . . . . . .

1254 1254 1255 1257 1257 1258 1259 1259 1259 1260 1261 1261 1262 1263 1263

⁎ Corresponding author. E-mail addresses: [email protected] (C. Askew), [email protected] (A.P. Field). 1 Chris Askew is now at the Faculty of Arts and Social Sciences, Kingston University, Penrhyn Road, Kingston upon Thames, Surrey, KT1 2EE, UK. 0272-7358/$ – see front matter. Crown Copyright © 2008 Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.cpr.2008.05.003

1250

C. Askew, A.P. Field / Clinical Psychology Review 28 (2008) 1249–1265

1. Introduction It is now 40 years since Rachman (1968) and Bandura (1969) famously suggested that individuals can acquire fear of an animal, object or situation vicariously, by witnessing another individual's fear of it. Rachman (1977) pointed out that vicarious learning was one of three pathways through which fears could be acquired. Historically, the dominant pathway to fear was believed to be direct conditioning in which individuals associate a neutral stimulus (the conditioned stimulus: CS) with some aspect of a traumatic event (the unconditioned stimulus: US) that elicits a fear reaction (the unconditioned response: UR). As a consequence, the stimulus subsequently comes to elicit a fear response itself (the conditioned response: CR) when encountered on its own. Rachman (1977) included vicarious learning as one of two additional pathways (the other being verbal threat information) that he labeled ‘indirect’. These indirect pathways were believed to give rise to less intense fears than direct conditioning. Despite widespread acceptance of vicarious (or observational) learning among researchers, until recently there was little experimental evidence in humans to support the proposition that fears and phobias can be acquired in this way. Much of the existing vicarious learning literature has been increasingly criticized on methodological grounds and until very recently there was no experimental research involving children. This is particularly surprising given that anxiety disorders are possibly the most common type of psychological disorder during childhood (Cartwright-Hatton, McNicol & Doubleday, 2006). In particular, specific phobias are one of the most prevalent psychological disorders in 15 to 54 year olds, with lifetime prevalence rates of 11.3% found in the National Comorbidity Survey (Kessler et al., 1994). They typically begin to develop during childhood or adolescence; 62% of animal phobias, for example, begin between 5 and 9 years old (Öst, 1987) and have a mean onset age of around 8.6 years old (Öst & Treffers, 2001). A further question is what the mechanisms underlying vicarious learning are, and under what conditions it is likely to occur. It has long seemed to be an implicit assumption of many authors that vicarious learning is underpinned by associative learning processes, but this issue has often received less direct attention in the literature. Given what is now known about the characteristics of associative learning and the implications this has for treating and preventing fears acquired in this way (see Field, 2006a), it is important to identify whether this assumption is correct. Taking into account the methodological issues raised and recent evidence with child samples the aim of this review is to re-examine the literature that fears can be acquired vicariously and consider the mechanisms underlying this learning (see Table 1 for a summary of the studies and their findings). To this end, a search of studies relating to ‘anxiety’, ‘fear’ and ‘vicarious learning’ was conducted using the Web of Knowledge (http://wok.mimas. ac.uk/). No studies that combined these terms were deliberately omitted from the review. 2. Early evidence for vicarious learning as a pathway to fear Over 20 years ago Green and Osborne (1985) reviewed the literature on vicarious learning generally. This section looks at the evidence up to that time for vicarious learning as a pathway to fear. It is fair to say that relatively little research on the vicarious learning of fear existed at that time because the bulk of experiments were concerned with social psychological phenomena, typically the transmission of attitudes and behaviors (for example, Bandura, Ross, & Ross', 1961, demonstration that aggression could be vicariously transmitted from models to children via social imitation with a “Bobo doll”). However, research did exist that demonstrated that adults could learn emotional responses by observing models in aversive conditioning procedures, even though they did not directly experience the aversive stimulus themselves (e.g. Berger, 1962; Bandura & Rosenthal, 1966; Brown, 1974; Vaughan & Lanzetta, 1980). It is these studies that we now review. 2.1. Experimental studies with adults In one of the earliest demonstrations of emotional vicarious learning, Berger's (1962) participants observed a (confederate) model move their arm sharply (the model's UR and observing participants' US) in apparent response to electric shocks (the model's US) following a buzzer sound (the model's and participants' CS). Participants showed increased galvanic skin responses (GSRs) during observation and continued to show GSRs (participants' CR) to the buzzer when it was later presented alone, indicating participants had learned to associate the buzzer (CS) with electric shocks and/or the model's negative response to the electric shocks (participants' US).2 Similar changes in skin conductance responses (SCR) have also recently been demonstrated for angry faces (CS) in participants observing a film in which models received electric shocks (model's US) and were detected even when the faces were masked and outside of explicit awareness (Olsson & Phelps, 2004). Likewise, Bandura and Rosenthal (1966) also successfully conditioned GSRs using buzzers and a model's apparent painful response to shock, discovering that the magnitude of the learnt response was related to the observer's level of emotional arousal during modeling. While this was the case at medium levels of arousal though, at higher levels this relationship was reversed; learning decreased as arousal increased. Using questionnaire data they obtained, Bandura and Rosenthal concluded that this was due to participants distracting themselves to limit the impact of the aversive situation they were witnessing when it was too intense. According to the authors, this could be one way in which vicarious learning differs from being directly involved in an aversive classical conditioning event: An individual observing might be able to attenuate the experience by shifting attention away from the event, or by replacing it with more pleasant imagined situations. However, as we will see, there is now compelling

2 Note, however, that stimulus–response (S–R) learning was assumed to occur during human conditioning at the time, rather than stimulus–stimulus (CS–US) learning, which is now known to be more common.

C. Askew, A.P. Field / Clinical Psychology Review 28 (2008) 1249–1265

1251

Table 1 Summary of the methodologies used to investigate vicarious learning and their conclusions Type

Method

Findings

Limitations

Conclusion

1. Experiments with non-anxious adults

Adults observed model receiving shocks that followed a neutral stimulus (e.g. buzzer or light)

Increased fear-related physiological responses (e.g. GSRs and heart rate) to stimulus measured in observer

(i) Ambiguity about mechanisms of learning (ii) Unclear whether effects were lasting (iii) Demonstrated in adults but not children

Evidence that physiological fear responses can be observationally learnt. But not clear that vicarious learning is implicated in the acquisition of actual persistent fears during childhood

2. Self-report in anxious adults and children

Questionnaire studies (usually used the POQ or OQ). Adults and children were asked about the origin of their fear or phobia

Many adults and children endorsed vicarious learning pathway in the origin of their fear

(i) Lack of control group, or similar levels of fear found in controls (ii) Often asked about events many years in past; hence potential for recall bias (iii) Validity of measurement instruments criticized

Evidence that actual fears were acquired in this way: many individuals attribute their fear to vicarious learning. However, the methodology of the studies has often been criticized. Provides no indication of the mechanisms underlying learning

3. Experiments with monkeys

Monkeys observed a model monkey responding fearfully to snakes

Observer monkeys learn lasting fear of snakes

Not known whether the findings can be extrapolated to humans

Convincing evidence that monkeys can acquire snake fear during observational learning events

4. Experiments with non-anxious children

Infants observed their mother responding negatively or fearfully toward a toy or stranger

Increased expression of fear and/or avoidance was observed in infants towards toys and strangers

No evidence that actual or lasting phobias are vicariously learnt

Children (7–9 year old) observed pictures of novel animals together with pictures of scared faces

Children showed increases in fear beliefs (for 3 months) and avoidance behavior for the animals

No evidence that actual phobias are acquired via vicarious learning

Demonstration that vicarious learning can lead to increases in fear expressions and avoidance in infants Showed that vicarious learning can lead to persistent changes in children's fear cognitions and increase avoidance behavior. Evidence that associative learning processes underlie vicarious learning

evidence that observational learning behaves similarly to direct classical conditioning in humans (Olsson & Phelps, 2004) and monkeys (Mineka & Cook, 1993) and is probably driven by the same associative mechanism (Field, 2006a; Mineka & Cook, 1993). 2.2. Interpretation of the model's experience and response In a further experiment Berger (1962) also used three additional control conditions: the model received a shock but did not move their arm; the model did not receive a shock but moved their arm; and the model did not receive a shock or move their arm. GSRs were significantly greater when observers saw the model move their arm sharply in response to an electric shock than in the other conditions. This was important to Berger because his definition of vicarious conditioning specified that an observer must be responding emotionally to a model's response and not solely to observed events, i.e. the electric shock or the arm movement. It was the observer's interpretation of the model's emotional state that was deemed to be crucial for vicarious learning. The importance of the interpretation of the model's internal emotional state for vicarious conditioning was also demonstrated by Kravetz (1974). One group of participants acted as observers and was informed that another participant, the model and actually a confederate, was being given electric shocks. A second group was told the model was performing a word task. Following a tone, participants in each group heard the model's heart rate either rise and fall or remain constant, but they did not have visual clues about what was actually happening. Auditory changes in the model's heart rate were found to be sufficient to vicariously condition changes in the observer's heart rate in participants who believed that the model was receiving electric shocks, but not for those who thought they were completing a word task, indicating that interpretation of the learning event was crucial. Furthermore, Kravetz demonstrated that the effects of the experimental manipulation were significantly greater when the CS and US were presented contiguously than when they were presented non-contiguously (control). The use of this control procedure suggested that vicarious learning was the result of the formation of CS–US associations.

1252

C. Askew, A.P. Field / Clinical Psychology Review 28 (2008) 1249–1265

2.3. The nature of the CS and US In terms of fear learning outside of the laboratory, it could be argued that the validity of the experiments is weakened because the CSs (e.g. buzzers and lights) are very different from the kinds of CSs known to be typically the objects of phobias (e.g. animals, heights, water, etc.). It might also be argued that there is a difference in what an observer believes is occurring in the experiments, compared to beliefs in a typical fear learning situation outside of the laboratory. It is unclear whether observing a model's pain during electric shock is the same as, for example, witnessing a parent's fear of a spider. In the first case there is clearly a CS followed by the model's painful response, along with the knowledge that the model is receiving an electric shock (is being physically harmed). The second scenario contains less information because there is only the CS (spider) and the parent's fear reaction to it. Such a difference might have some relevance if, as experiments appear to have shown, the interpretation of responses to events is crucial for vicarious learning. In all of the studies previously described the model's US (e.g. electric shock) would have also have been effective at producing direct-learning in the observer if they had been directly involved in an aversive classical conditioning experiment. It is not possible to rule out the possibility that the model's US had itself a disproportionate influence on the observer compared to the model's response (see Fig. 1). Accordingly, Bandura (1969) argued that the best way to demonstrate vicarious learning is to design an experiment in which the observer's emotional response can be due only to the emotional expression of the model. This could be best achieved, he suggested, “by ensuring that the stimuli which elicit emotional responses in the performer are either unobservable by, or of neutral valence to, the observing subject.” (p.169). By using a neutral tone as the model's US, Hygge (1976) conducted an experiment that seems to fulfill Bandura's criterion. Crucially, observing participants were led to believe that the tone they experienced as neutral was very painful for the model. Significant GSRs were found in response to a light which had signaling the occurrence of the tone, indicating again that the observer's interpretation of the model's response was crucial for vicarious instigation. In terms of the clinical literature, a concern raised by Hygge and Öhman (1978) was that despite demonstrations of vicarious learning in experimental studies, there was little evidence that typical phobias would actually be acquired in this way. To address

Fig. 1. A typical early vicarious learning procedure (e.g. Berger, 1962). It was assumed that during vicarious learning the observer learnt a negative response (CR) to the buzzer (CS) after associating it with a model's response (US) to electric shocks. Note that for learning to occur for the observer, the model's response could be either to his or her US (shock in this example), directly to the CS, or both. A further ambiguity is whether the observer is responding exclusively to the model, or also to the electric shock.

C. Askew, A.P. Field / Clinical Psychology Review 28 (2008) 1249–1265

1253

this, Hygge and Öhman presented participants with three picture stimuli: two as a CS+ and US pairing and the third as an unpaired CS−. Four separate groups saw different combinations of fear-relevant pictures (snakes, spiders and rats) and fear-irrelevant (mushrooms, berries and flowers) as CSs and USs. During the habituation phase, participants witnessed another participant, who was in fact a confederate, being told that there was concern about the levels of her skin conductance responses to one of the picture stimuli; she explained that she had a phobia for the stimulus. The confederate, who appeared to need persuasion to continue with the experiment, acted as the model and her phobic stimulus was the US. Vicariously instigated SCRs were found for participants in response to both fear-relevant and fear-irrelevant CSs that had been paired with the US towards which the model acted fearful. Moreover, although acquired SCRs for fear-irrelevant CSs were extinguished during an extinction procedure, SCRs for fear-relevant CSs persisted, indicating a difference in the robustness of learning for fear-relevant and fear-irrelevant stimuli. As in Hygge's (1976) study, observers did not need to witness an event that would also be potentially aversive for them: the US was considered threatening only to the model and not to observers themselves. The study confirmed that the essential requirement for vicarious learning is that the observer receives information about the model's response to a stimulus. This information is then used by the observer to infer the model's emotional response (Hygge and Öhman, 1978). 2.4. Measurement of the fear response There is little doubt that individuals with intense animal fears experience measurable physiological responses when they look at their feared animal, including changes in skin response, heart rate, and blood pressure (Globisch, Hamm, Esteves, & Öhman, 1999). Nevertheless, some authors have proposed that the assumption that autonomic responses indicate fear may not be reasonable. Vaughan and Lanzetta (1980) argued that changes in heart rate are also influenced by task demands and movement requirements, and skin conductance can also be used to measure distress, orienting, or anxiety. Accordingly, in addition to skin conductance measures, Vaughan and Lanzetta's vicarious learning paradigm used Electromyography recording to measure facial expressions, which they suggested was a more specific measure of emotional arousal. The learning event consisted of a video film of a model displaying pain in response to shocks (the observer's US) which followed an attempt to memorize certain word-pairs (CS). Vaughan and Lanzetta found that changes in both observers' skin conductance responses and facial expressions occurred during modeling, their facial reactions being similar to if they themselves were in pain. They also found that learnt skin conductance responses and facial expressions to later CS-alone presentations were similar to if they had themselves been anticipating a shock. However, these findings occurred only when observers were aware of the CS–US contingencies, leading Vaughan and Lanzetta to believe cognitive involvement was probably necessary for vicarious learning to take place. One interesting finding from Vaughan and Lanzetta's (1980) study was that facial expressions instigated in the observer during modeling differed from those subsequently produced during CS-alone presentations. Based on previous evidence, the experimenters interpreted observers' facial expressions in response to the model as a pain or distress response, whereas those instigated during CS-alone presentations were thought to indicate anxiety or fear. Hence, the observer's facial reactions to the CS appeared to be more similar to the model's response to the CS (i.e. anxiety or distress) than the model's response to the US (i.e. pain or distress). This was important because it contradicted a previous assumption that the observer's conditioned response to the CS is identical in type (though not necessarily in magnitude) to the model's response to the US and the emotion instigated in the observer during modeling. Vaughan and Lanzetta proposed a more complex model of vicarious conditioning that accepted differences between vicariously instigated and conditioned responses: Whilst a parent's distress toward a stimulus may instigate any number of emotions in their child, the stimulus may subsequently merely evoke anxiety in the child when presented alone. Indirect support for this also came from a study by Craig and Lowery (1969). Whilst heart rate increases would be expected in anticipation of receiving electric shocks first hand, Craig and Lowery recorded heart rate decreases (but increased GSRs) when participants observed a model receiving shocks. It is now clear that this is not a unique attribute of vicarious learning; direct conditioning episodes also do not necessarily result in a CS eliciting the same type of response as the US (Rescorla, 1988). Thus Vaughan and Lanzetta's findings lend support to, rather that challenge, the view that vicarious learning is a form of associative learning. 2.5. Limitations Green and Osborne (1985) concluded in their review that it was not possible to determine what factors determine whether vicarious learning will occur. The main difficulty appears to be knowing what stimulus acts as the US, which is complicated by the fact that the majority of experiments until this time used a procedure in which an observer watches a model in an apparent aversive conditioning procedure. The model's US is frequently explicit and usually threatening (e.g. electric shock), so the observer could have actually been responding to the model's US. In addition to some studies not successfully isolating the effectual US, Green and Osborne suggested that in other studies the instructions given to participants by experimenters may sometimes act as a further confounding factor, because information about the model's US or the model's UR may also influence the observer's response. However, these criticisms do not appear to create serious problems for Hygge (1976) and Hygge and Öhman's (1978) experiments and these studies remain very persuasive. In relation to fear and phobia acquisition, there may also be a number of interpretative limitations. First, the central deceit in most studies is that the model is physically hurt: The observer is essentially observing someone else's aversive conditioning experience. Whilst vicarious fear learning may occasionally occur in this way outside of the laboratory (e.g. when someone is attacked by a dog), it seems likely that often there may only be a model responding fearfully to a stimulus

1254

C. Askew, A.P. Field / Clinical Psychology Review 28 (2008) 1249–1265

without being harmed physically (e.g. a parent might show fear to a dog without that dog attacking them). Further, although Hygge and Öhman's (1978) methodology overcame this problem by using a US that was not threatening to the observer, it still utilized a CS, US (though not threatening to the observer), and a model's reaction to the US, whereas outside of the laboratory often only a CS and the model's reaction to it appear to be present. Although this distinction is worth noting, it is unclear how important it is: as we shall see more recent vicarious learning studies with children (Askew & Field, 2007; Gerull & Rapee, 2002) and monkeys (e.g. Cook & Mineka, 1989) have demonstrated vicarious learning without an overt US to which the model is responding. In addition to Green and Osborne's concerns, there are other limitations to the clinical application of these early findings. First, although these experiments showed that emotional reactions can be learnt for the duration of the experiments, there is little evidence that these responses are lasting (Mineka & Zinbarg, 1996). To formulate a theory that lasting fears and phobias are acquired in this way we would first need to show that vicarious learning effects endure. Moreover, we know that specific phobias typically develop during childhood and the question remains whether vicarious learning is also demonstrable in children. Further, physiological measures are not the only indicators of fear responses. Lang (1968) famously suggested that anxiety is indicated in three relatively independent response systems: physiological responses, language behavior (subjective report), and overt behaviors (avoidance). Second, although most of these early studies assumed that associative learning mechanisms underpinned vicarious learning, very few authors set out to test this assumption. This is important for developing interventions and preventions that target this pathway. Once the mechanism of learning is well understood it becomes easier to prevent that learning or to weaken it. Finally, although the experimental methodology allowed firm conclusions that vicarious learning could causally create fear, this did not mean that the pathway is one that is actually implicated in clinical fears. This concern probably explains why much of the clinical research for the next 20 years was dedicated to exploring vicarious learning in already anxious individuals. 3. Retrospective self-report in already anxious humans 3.1. The Phobic Origin Questionnaire A large proportion of the evidence from clinically anxious individuals has been obtained using the Phobic Origin Questionnaire (POQ: Öst and Hugdahl, 1981). The POQ assesses the relative roles of Rachman's three proposed pathways in the etiology of phobias, and is formed of nine ‘yes’ or ‘no’ questions and one open-ended question. The yes/no questions obtain information allowing the origin of the phobia to be designated as direct conditioning, vicarious learning, informational events, mixed onset, or no recall. The open-ended question asks for any further information relevant to the fear. On the whole, researchers using the POQ have found that individuals with mixed phobias tend to endorse a direct conditioning pathway for their fear (57.5% to 78%), with vicarious learning as the second most reported pathway (17% to 42%), followed by information-type (10.4% to 25%) pathways (Merckelbach, De Ruiter, van den Hout, & Hoekstra, 1989; Öst and Hugdahl, 1981). Typically, specific acquisition pathways have been found to be more important for certain types of fears. A number of studies (Öst, 1985, 1987, 1991; Öst & Hugdahl, 1981, 1985) found that vicarious learning pathways were reported primarily in animal (22% to 27.5%) and blood phobias (24% to 25%), followed by dental phobias (12% to 15.6%) and social phobias (12.9% to 15.6%), and also to a lesser extent in claustrophobia (6.5% to 8.6%) and agoraphobia (5.6% to 8%). For all types of phobia, studies for the most part report figures lower than those endorsing direct conditioning pathways. Several authors have concluded that a combination of more than one pathway was the most common cause of fear (e.g. Merckelbach et al., 1989; Ollendick & King, 1991). Different average ages of onset have been found for each of the pathways. Phobias reportedly acquired via information or vicarious learning routes have an earlier onset than those acquired via direct conditioning (Öst, 1987), leading Öst to suggest that even individuals reporting direct conditioning causes may have had an earlier vicarious learning experiences prior to the recalled direct conditioning event which may no longer be remembered. Some support for this comes from a study by Withers and Deane (1995) which suggested the possibility that direct conditioning events may be more readily remembered than indirect conditioning events. Öst and Hugdahl (1981) used the POQ to examine Rachman's (1977) proposal that indirectly acquired fears are likely to be milder than those acquired directly. Whilst this appeared to be the case for animal phobias, it was not the case for claustrophobia or social phobia, although the authors suggested the range of fears represented in their sample may not have been great enough to adequately test the hypothesis. Merckelbach et al. (1989) also investigated this issue and found no differences between ratings of physiological and cognitive symptoms for patients reporting direct or indirect pathways. It appears then that fears acquired via vicarious learning may often be subjectively just as intense as those acquired by direct conditioning. 3.2. Structured interview and other questionnaires Structured interviews have also been used to explore the origins of individuals' fears. This method of enquiry has sometimes found vicarious learning events less important in animal phobias than the POQ studies. McNally and Steketee (1985) found 77% (n = 17) of their sample of 22 severe animal phobics could not recall the onset of their phobia, reporting that their fears had been

C. Askew, A.P. Field / Clinical Psychology Review 28 (2008) 1249–1265

1255

there as long as they could remember. Of those that did recall a specific event, five attributed their fear to conditioning, one to verbal information-type causes, and only one to vicarious learning. Another study by Kleinknecht (1994) classified responses to a direct question about the circumstances leading to the development of blood fear into different types of onset. Only 15.5% of the sample reported vicarious learning experiences as the primary cause of their fear. The findings are complicated by other differences in methodology however. In contrast with much of the POQ evidence, for example Öst's (1991) sample of blood phobics who were undergoing or had recently had treatment, Kleinknecht's sample was a group of undergraduates classified as fearful by questionnaire. They are likely to have had less intense fears, which may have led to differences in findings. Also using structured interviews, Rimm, Janda, Lancaster, Nahl and Dittmar (1977) found direct conditioning experiences were reported as the main cause of fear by their phobic sample (35%). Those who had no memory of any related causal events (29%) and those recalling non-specific events (20%) were the next largest groups, while verbal instruction (9%) and vicarious experiences (7%) were the least common causes reported. In contrast, when Murray and Foote (1979) asked three groups of undergraduates with low, high and phobic levels of snake fear what kind of experiences they had previously had with snakes there was little evidence that direct conditioning played a major role in the acquisition of their fear. In regard to vicarious learning, the phobic group reported significantly more events in which they had observed someone having a negative experience with snakes than the low-fear group. They also reported more negative information about snakes from parents, television, films, books, and newspapers, and negative information correlated with levels of snake fear. The wide range of experiences described as negative information, including visual mediums such as television and films, may also indicate that observational learning played some role in their fear. 3.3. Limitations of the self-report literature Although the POQ and other self-report measures have found considerable support for a vicarious learning pathway to fear, several methodological issues have been raised in relation to: (1) the lack of control groups; (2) potential memory bias; and (3) the validity of the measurement instruments. Di Nardo et al. (1988) noted the lack of control groups with either no- or low-fear individuals in the majority of self-report studies. Consequently it was not possible to know whether particular types of learning event were more prevalent among individuals with fears than those without. In a study of high and low dog-fearful participants, Di Nardo et al. found that direct conditioning experiences (in most cases bites or scratches) were reported by the majority of individuals in the high fear group (56%); however, this was not significantly greater than the number of reports in the low-fear group (66%). Similar findings have also been found for spider phobia (Merckelbach, Arntz, Arrindell & De Jong, 1992). Comparing fearful and non-fearful undergraduates' reports, Hekmat (1987) also found that animal phobics had not experienced significantly more negative vicarious learning episodes than a group of non-fearful students. Similar observations have been reported in public speaking anxiety (Hofmann, Ehlers & Roth, 1995) and driving phobia (Ehlers, Hofmann, Herda & Roth, 1994). Moreover, as we have seen, participants with high snake fear did report significantly more vicarious learning experiences than those with low snake fear in Murray and Foote's (1979) study. Nevertheless, most authors are agreed that overall the evidence indicates that having an aversive experience with a stimulus is not sufficient to predict whether an individual will come to fear it. One explanation may be that individuals with fears have had a qualitatively different type of learning experiences to those without fears. Merckelbach et al. (1992) have also noted that whilst the memory of an experience is asked for in the POQ, the actual intensity of that experience is not taken into account. It seems feasible that intensity of experience is a factor in whether a phobia develops. Additional explanations are likely to be that individuals differ in temperament (e.g. Mineka & Öhman, 2002; Mineka & Zinbarg, 2006; Muris & Merckelbach, 2001) and in previous learning histories (Davey, 1997; de Jongh, Muris, Ter Horst & Duyx, 1995; Doogan & Thomas, 1992; Field & Davey, 2001; Mineka & Zinbarg, 2006), so that two people can experience the same incident and only one subsequently develops fear. Another problem, noted by Ollendick and King (1991), is that of recall bias. Specific phobias typically begin during childhood; animal phobias, for example, have a mean age of onset of about 7 years old (Öst, 1987). However, the youngest participants in most studies were of undergraduate age. Given that they may have been asked to recall events from 10 to 20 years earlier, it is perhaps unsurprising that many adults reported that they could not remember how or when their phobia began. This problem is illustrated by McNally and Steketee's study, in which over two thirds of the 22–57 year old sample could not remember the onset of their phobias. Further, when causal attributions are made they may be inaccurate (Taylor, Deane & Podd, 1999; Withers & Deane, 1995). Investigating fear of dogs in undergraduates and 8 to 9 year olds, Doogan and Thomas (1992) found that only half of dog-fearful adults could remember the onset of fear. High dog-fearful adults did not recall more painful experiences with dogs than low dogfearful adults. There was also no evidence that high fear adults or children had had more vicarious learning experiences than those with low fear, though high fear children did report receiving more negative information in the form of verbal warnings about dogs than low-fear children. In contrast, when King, Clowes-Hollins and Ollendinck (1997) asked parents to endorse the most likely pathway to their child's (aged 2 to 12 years old) dog fear, vicarious learning was reported as the most common cause of their children's phobia (53%). A number of parents also reported fear of dogs themselves, stating that they acted nervously around dogs, which could suggest that their children were provided with opportunities to vicariously learn their fear of dogs, but this awareness of their own behavior might also make them more likely to attribute their child's fear to vicarious learning. Ollendick and King (1991) examined the origins of common fears in school children (aged 9 to 14 years). The majority of children reported vicarious learning (56%) or informational (89%) factors, with fewer mentioning direct conditioning experiences (36%). In the case of some of the items (e.g. ‘snakes', ‘earthquakes’, ‘burglars breaking into our house’), experiences via both indirect

1256

C. Askew, A.P. Field / Clinical Psychology Review 28 (2008) 1249–1265

pathways appeared to have been necessary if fear was to reach a high level. For other items (e.g. ‘not being able to breathe’, ‘falling from high places’, ‘being hit by a car or truck’) it appeared that a combination of direct and indirect conditioning experiences was necessary before high levels of fear developed. For the vast majority of the children and adolescents one type of experience, direct or indirect, was not sufficient to evoke high levels of fear. This led the authors to conclude that the three pathways were interactive and more potent when combined. One reason that evidence for vicarious learning and informational experiences is particularly striking in Ollendick and King's study may be because of the younger age group, that had access to more recent (and possibly more accurate) memories about the onset of fear. Third, the measurement instruments have come under fire. Menzies and colleagues (e.g. Menzies, 1996; Menzies and Clarke, 1993a; Menzies & Clarke, 1994; Menzies, Kirkby, & Harris, 1998; Poulton & Menzies, 2002) have been the most prominent and consistent critics of the methodology used to investigate the acquisition of fears and have challenged the assumption that fears and phobias necessarily develop via one of Rachman's three pathways. The authors support a non-associative account of fear acquisition, viewing some phobias to be the result of genetic influences, in which fear of certain ‘evolutionary-relevant stimuli' occurs on first encounter. It is argued that the POQ overestimates the importance of direct and indirect pathways because of an inherent assumption that a phobia's onset is attributable to one of Rachman's pathways, which means participants are forced to ascribe the onset of their phobia to either direct conditioning, vicarious learning, information, or a mixture of pathways (Menzies & Clarke's, 1993a). To overcome this problem, Menzies and Clarke developed the ‘origins questionnaire’ (OQ: Menzies & Clarke's, 1993a), which acknowledges non-associative learning causes. The OQ asks participants to describe experiences relating to their feared object or situation occurring prior to the onset of their fear, and avoids asking participants to make direct causal attributions. Menzies and Clarke argue that the OQ, unlike the POQ, also categorizes individuals who have always had a fear and those who can remember a time when they did not have the fear but not events associated with its onset. Some authors have also suggested that the POQ's convergent validity is low (Kheriatry, Kleinknecht, Hyman, 1999; Menzies et al., 1998). In contrast, the OQ is argued to have both convergent validity and interrater reliability (e.g. Menzies & Clarke's, 1993a; Menzies & Clarke, 1995a). Compared to the POQ, OQ studies have typically found much lower numbers of participants endorsing a vicarious learning pathway (Kirkby, Menzies, Daniels, & Smith, 1995; Menzies, 1996). Menzies and Clarke (1993a) found a large proportion of height-fearful undergraduates reporting either non-associative (traumatic) events, or that their fear had always been there. Although 20% attributed their fear to vicarious learning, similar levels were also found in a non-fearful control group. Comparable results were also found by Menzies and Clarke (1995a): a substantial number of participants with height phobia reported vicarious learning causes (15.5%), but again this was no different from a control group. The majority claimed either that they had always been afraid of heights (38.5%) or that they could not remember how the fear started (9.5%). Similarly, in an OQ study of water fear, a large number of parents (56%) stated their child had been afraid of water on first contact, though a substantial proportion (26%) believed that vicarious learning experiences were the most influential factor in the development of fear (Menzies & Clarke, 1993b). The non-associative explanation for water phobia gained further support from a study by Graham and Gaffan (1997) that utilized a questionnaire modeled on Menzies & Clarke (1993b). The non-associative argument is that avoiding height and water was important to our ancestors' survival and consequently natural selection has favored those who avoided them. Poulton and Menzies (2002) have proposed that non-associative causes represent a fourth pathway to fear for certain evolutionary-relevant fears. But non-associative interpretations of the findings are also problematic. A central assumption is that lack of recall for a learning event is indicative that no learning took place—i.e. that the fear was acquired non-associatively (e.g. Menzies & Clarke, 1995b; Poulton & Menzies, 2002). However, lack of recall may merely indicate poor memory, rather than evidence of non-associative learning (Forsyth and Chorpita, 1997). Animal phobias begin at a fairly young age, typically between 5 and 9 years old (Öst, 1987), and may in some cases overlap with childhood amnesia (Kheriaty et al., 1999; Pillemer, 1998). This problem may be particularly relevant for indirect pathways because they may be more likely to be forgotten than direct traumatic conditioning experiences (Withers & Deane, 1995). A further problem for both the OQ and POQ is that it is not clear that individuals recalling an event are correctly remembering an incident crucial to the onset of their fear, or that those that state they were always afraid actually were. Taylor et al. (1999) used a version of the OQ with a drivingfearful sample and found that after only 1 year 46% of the sample had changed the pathway to which they ascribed their fear. Of those who had attributed their fear to associative causes (either conditioning or one of the two indirect pathways) only 56% still claimed this a year later. For example, four participants initially reported that they had been fearful since a conditioning experience had occurred; 1 year later all four reported that they had always been fearful. Similar changes in attribution were also found in the other direction. A final issue for both the POQ and OQ is that they measure an individual's beliefs about the cause of their fear, but this may not be the actual cause. One study by Merckelbach, Muris, and Schouten (1996) addressed one of the criticisms of the POQ literature, comparing the reports of a group of children and adolescents' (9 to 14 year olds) with those of their parents. A revised version of the POQ asked whether children had already been afraid prior to a reported event and gave children and parents a “have always been afraid” option. Although a large proportion of children and parents endorsed a direct conditioning pathway (almost 41%), a similar amount of children (46%) stated that they had always been afraid. Vicarious learning and information appeared to have contributed to the chronic development of fear, but not the actual onset of fear. One interesting finding from Merckelbach et al.'s (1996) study was that mothers, but not fathers, appeared to act as models for children who endorsed a vicarious learning explanation for their fear. This is also supported by a study from Muris, Steerneman, Merckelbach and Meesters (1996) examining parental modeling in 9– 12 years olds with a variety of psychopathological symptoms including anxiety disorders. Measures of fear and anxiety were taken for both children and their parents, and parents were also asked how often (almost never, sometimes or often) they expressed their

C. Askew, A.P. Field / Clinical Psychology Review 28 (2008) 1249–1265

1257

fear in front of their child. A positive association between parents' (mother: r = .34, father: r = .31) and children's trait anxiety scores was found and children's fear levels were positively associated with their mother's (r = .56), but not their father's (r = .17), fear levels. Particularly significant for the vicarious learning literature was that the highest and lowest levels of fear were found in children of mothers who most and least frequently expressed fear in front of their child respectively. Although they successfully addressed many of the criticisms of the self-report literature, Muris et al.'s (1996) study looked only at general levels of fearlessness, and not at specific fears or phobias. In another study, 57.1% of a sample of school children reported to Muris, Merckelbach and Collaris (1997) that they had experienced vicarious learning events associated with their (non-clinical) fear of animals. However, none of the children believed that vicarious learning had either caused or intensified their fear; similar results were found for fear of spiders, fear of failure and criticism, and medical fears. Thus, together these results seem to imply that vicarious learning may influence general levels of fearfulness, but not fear for specific stimuli. There are limitations to what the self-report literature can tell us that is clinically useful. Kleinknecht (2002), for example, has suggested that, “retrospective accounts should be viewed at best as suggestive and hypothesis generating rather than hypothesis supporting or disconfirming” (p. 160). Self-report measures are also likely to measure people's attributions which may, or may not, reflect how their fear was actually acquired; it is one thing to believe that your fear can be explained by vicariously learning but quite another to show the vicarious learning actually can have a causal role in the development of fear. This is of course the complete opposite of one of the problems of the experimental research, which showed a causal role of vicarious learning in fear acquisition but could not demonstrate a direct link to clinical fears. In combination, these complementary approaches have left us with good reason to think that vicarious learning plays a role in clinical anxiety. However, this retrospective research still leaves us searching for an underlying mechanism that can be exploited for clinical prevention and intervention. In addition, the evidence from self-report research is often conflicting: vicarious learning experiences are reported in the onset of a sizeable proportion of fears, with anywhere up to half of individuals reporting such experiences, whereas, other studies find very little evidence for a vicarious learning history. Some evidence indicates that multiple pathways may be involved (Merckelbach et al., 1989) and other evidence that the pathway of acquisition may be related to the age of onset or type of phobia (Öst, 1987). The fact that multiple pathways are implicated in clinical fears is in no-way surprising, and although it is useful to study pathways to fear in isolation in the laboratory, in the real world learning experiences are not so conveniently compartmentalized. One of the great challenges to researchers studying the acquisition of fears is to use methodologies that look at how pathways combine to create fears. 4. Monkey business Some of the most persuasive evidence for vicarious learning of fear comes from a series of observational learning studies with rhesus monkeys (Macaca mulatta) by Mineka, Cook, and colleagues (e.g. Cook & Mineka, 1989, 1990; Mineka & Cook, 1986, 1993; Mineka, Davidson, Cook, & Keir, 1984). The studies were developed from the finding that laboratory-reared rhesus monkeys do not display the fear of snakes that their counterparts in the wild commonly exhibit, indicating that fear of snakes is not innate in rhesus monkeys (Joslin, Fletcher, & Emlen, 1964; Mineka et al., 1984; Mineka, Keir, and Price, 1980). However, it also seems unlikely that every wild-reared monkey has directly experienced a traumatic conditioning event involving a snake and a more likely explanation appears to be that wild monkeys acquire fear by observing other monkeys interacting fearfully with snakes (Joslin et al., 1964; Mineka et al., 1984). Furthermore, it would be more advantageous from an evolutionary perspective if avoidance of a potentially dangerous stimulus could be learnt without first having a life-threatening encounter with it. 4.1. Can monkeys acquire fears observationally? In Mineka et al.'s (1984) first study laboratory-reared monkeys (observers) without snake-fear watched their wild-reared, snake-fearful parents (models) interact with real, toy, and model snakes. After only 8 mins, five of the six monkeys had acquired fear of snakes, and demonstrated both fear and avoidance behavior with snakes and snake-like stimuli compared to a neutral object. Fear was still present 3 months later and proved not to be context-specific: fear was measured in contexts other than the one in which it was formed. In addition, the number of disturbance behaviors exhibited by model monkeys correlated with those exhibited by their offspring post-learning. Cook, Mineka, Wolkenstein and Laitsch (1985) replicated Mineka et al.'s findings using unrelated monkeys demonstrating fear responses in two of Lang's (1968) three fear-response systems: behavioral avoidance and signs of distress (which were taken as evidence of a subjective state of fear that in humans Lang termed the ‘language behavior' response system). They also found that a model's behavior predicted the degree of an observer's learnt behavior, concluding this was due to the closeness of modeling occurring: monkeys were unrelated, so it could not be due to genetic similarities in temperament. In the second part of their study, Cook et al. showed that the observing monkeys also successfully acted as models for a new group of non-fearful observer monkeys, indicating that observational learning is an effective process for transmitting fear between successive groups of rhesus monkeys. Fear acquired in the second experiment was less intense than in the earlier one, appearing to be because the model's vicariously acquired fear (in Experiment 1) was not as robust as a wild-reared monkeys' fear, so fear levels decreased during the modeling phase. The authors proposed that wild-reared monkeys' fear is likely to be more robust because, unlike the lab-reared monkeys, they have experienced more varied exposure to a number of models in the wild. Truly robust fears may require varied and repeated vicarious learning episodes. One apparent disparity between findings from non-human primate studies and clinical research is that if humans acquire fears as rapidly and easily as rhesus monkeys we might expect a higher concordance between the fears of parents and their children than is found (Mineka & Cook, 1986). Mineka and Cook noted however, that whilst the monkeys had little prior exposure to snakes,

1258

C. Askew, A.P. Field / Clinical Psychology Review 28 (2008) 1249–1265

humans may have had some form of previous exposure before they observe a fearful parent. It is known that prior experience of a stimulus (i.e. an individual's learning history) can inhibit conditioning during a subsequent learning event in a process called latent inhibition (Lubow, 1989; Siddle, Remington & Churchill, 1985). Accordingly, Mineka and Cook explored whether positive modeling would inhibit fear learning in monkeys by exposing them to positive models interacting without fear with snakes prior to the observational learning procedure used in previous experiments. Six out of eight monkeys exposed to this ‘immunization’ procedure showed little or no acquisition of snake fear after observing the fearful models, implying that non-fearful vicarious experience of a stimulus may inhibit future fear-learning. As discussed earlier, self-report studies show that not everyone reporting negative vicarious learning experiences with animals develops a fear of them (Hekmat, 1987). Given that humans do not enter vicarious learning events as naïve blank slates, Mineka and Cook's experiment may explain this finding. Another implication is that children may be particularly susceptible to vicarious learning because of their relatively limited experience of stimuli (Davey, 1992). Also, it suggests that vicarious learning shares one of the well-established characteristics of associative learning. Using monkeys that had already acquired fear in previous observational learning experiments, Cook and Mineka (1987) investigated the characteristics of observational learning further. A striped box that was presented together with a snake also came to evoke a fear response in observers via its association with snakes, demonstrating second-order conditioning, a further wellestablished feature of conditioning (Rescorla, 1980). This demonstrates that a fear response associated with one stimulus via observational learning can also be elicited by a second if it is presented contiguously with the first, even though the second stimulus is never experienced with an aversive US. This second-order conditioned fear was not found to be especially robust however, and drawing on the theory of preparedness (Seligman, 1971), the authors suggested the lack of robustness may have been due to the lack of fear-relevance of the second-order CS (the box). In support of this, Hygge and Öhman (1978) had earlier shown that vicariously learnt responses were very difficult to extinguish when the CSs were fear-relevant, but not when they were fearirrelevant. Further support for a preparedness explanation came from several experiments which used edited video to present films of monkeys interacting fearfully with fear-relevant stimuli (snakes and a toy crocodile) or fear-irrelevant stimuli (flowers and a toy rabbit). The choice of the new stimuli was based on the observation that rhesus monkeys in the wild fear crocodiles but not rabbits. Observational fear acquisition was demonstrated for both fear-relevant, but not fear-irrelevant stimuli (Cook and Mineka, 1989, 1990). A further implication was that even video presentations of models interacting fearfully with stimuli are sufficient for vicarious learning to occur, suggesting that films and television could also create or contribute to fears; not just real world events (Mineka & Zinbarg, 1996). These studies indicate that vicarious learning may occur only for certain types of stimuli for which there is an evolutionary disposition to learn fear, presumably because of the threat these fear-relevant stimuli pose to the survival of rhesus monkeys. Many authors view this as evidence supporting Seligman's (1971) theory of preparedness (Cook and Mineka, 1989, 1990; Mineka & Öhman, 2002; Öhman & Mineka, 2001). But others have challenged this assumption; Davey (1995), for example, has noted that non-primates typically acquire fear for fear-irrelevant stimuli relatively easily via observational learning (e.g. Del Russo, 1975; Kohn, 1976; Mason & Reidinger, 1982) and as we shall see, recent evidence suggests children can vicariously acquire fear-related cognitions and behaviors for fear-irrelevant stimuli (Askew & Field, 2007; Dubi, Rapee, Emerton & Schniering, 2008). 4.2. Exploring the mechanism of learning We mentioned before that in early experimental work, the assumption was that vicarious learning operated through associative learning mechanisms. This is the view of some authors (Field, 2006a; Mineka & Cook, 1993; Olsson & Phelps, 2007), but it had not been tested. Like early vicarious learning experimenters, Mineka and Cook (1993) argued that a model monkey's fearful reaction (the observer's US) to the snake stimuli (CS) elicits a fear response (UR) in the observer, so that snakes subsequently come to elicit a conditioned fear response (CR). If this is the case, it would mean that associative learning mechanisms underlie observational learning (i.e. it is a form of ‘conditioning’). One of the great innovations of the Monkey research was that Mineka and Cook demonstrated that observer monkeys' fear (UR) while watching the trials correlated with model monkeys' fear behavior (observers' US). However, as noted previously, it has not always been clear from many of the human experimental studies whether the observer was reacting to the model's US, the model's UR, or both. With this in mind, Bandura (1969) maintained that the most effective way to demonstrate vicarious learning would be to design experiments in which any emotions instigated in the observer are due solely to the emotional expression of the model. Mineka and colleagues, experiments satisfy this criterion because if lab-reared monkeys do not already fear snakes there is no observable stimulus other than the model's reaction that could act as the observer's US. To investigate whether features of the snake itself were acting as a US, Mineka and Cook (1993) devised an experiment in which some of the observer monkeys could not see the snake stimuli during learning. Observers were found to react with similar levels of distress even when they could not see what the model was reacting to, leading to the conclusion that only a model's exhibition of emotion, and not the snake, was acting as the US. Mineka and Cook (1993) also noted that a slightly different explanation is not ruled out by their observational learning procedure: it is also possible that the procedure represents a form of second-order conditioning. In this scenario, a model's distress (CS1) becomes associated with a co-occurring traumatic experience (US), so that the model's distress subsequently elicits a fear-related response (CR) in the observer. During observational learning the observer comes to associate snakes (CS2) with the model's distress (CS1), so that snakes also elicit the fear response (CR). The evidence from monkeys does not distinguish between these two possible mechanisms, but either way it does demonstrate that vicarious learning in non-human primates can be conceptualized in terms of associative learning processes.

C. Askew, A.P. Field / Clinical Psychology Review 28 (2008) 1249–1265

1259

4.3. Clinical implications from work using monkeys Mineka and Cook's work is so compelling because it takes the earlier experimental work that showed that vicarious learning caused fear, but using stimuli completely novel to the monkeys, thus making a good analogue of the learning experiences that a child would have. Furthermore, they have shown that vicariously learnt fears affect not just subjective states of distress, but avoidance behavior (a second of Lang's emotional response systems). They have also used the paradigm to explore the mechanisms underlying the learning (see the next section), which as we have mentioned before is vital to inform prevention and intervention. Their work has shown that vicariously acquired fears to novel stimuli persist up to three months, and to re-iterate our earlier point this is critical to demonstrating that vicarious learning can lead to persistent clinical fears. Finally, their ‘immunization’ study has direct clinical relevance in showing that it is possible to prevent fears from being vicariously learnt, and that some fears are more easily learnt than others. However, to extend this research to humans an assumption has to be made that the processes underlying vicarious fear learning developed very early in human evolution and that rhesus monkeys are evolutionarily similar enough to humans for reasonable comparisons to be made. If this is the case, as appears likely, the results have important implications for the vicarious learning of fear in humans. However, because of their ability to use language humans are likely to engage in cognitive processes that are qualitatively different to those of rhesus monkeys; therefore direct extrapolation from the behavior of one to the other may not always be appropriate. 5. Research in non-anxious children The past 20 years saw two important strands of research develop into the vicarious learning of fear. Self-report data from anxious adults showed that people with clinical anxiety could identify vicarious learning as a potential route through which their fear developed. However, this research could not show the causal role of vicarious learning nor could it uncover the fundamental psychological mechanisms driving the learning. The second strand of research on monkeys, however, did show that long-term fears could be acquired vicariously, and that associative learning mechanisms could explain this learning. However, these findings needed to be extended to humans. We know that fears and phobias actually tend to begin at a fairly young age (e.g. Öst, 1987; Öst & Treffers, 2001). Children have also had relatively less opportunities for prior learning than adults. Finally, all of the evidence reviewed so far has looked at vicarious learning in isolation without considering how it interacts with other learning. Given these various interpretative restrictions, research with children was needed. Clearly it would not be ethically desirable to utilize comparable experimental procedures with younger populations and so the challenge has been to design analogous procedures appropriate for the study of vicarious learning in children. 5.1. Social referencing and vicarious learning with infants Several studies related to the social referencing literature have successfully used experimental procedures with infants to show vicarious learning of fear. Social referencing refers to the emotional communication that takes place when individuals actively search for other people's interpretations of a situation or stimulus to aid formation of their own appraisal (Feinman, 1982). Studies typically present infants with an ambiguous situation and examine how a caregiver's emotional signaling influences the infant's affect and behavior. Sorce, Emde, Campos, and Klinnert (1985) adapted Gibson and Walk's (1960) seminal research with the ‘visual cliff’ to examine how, in an ambiguous situation, infants seek information from the facial expressions of their mothers. The visual cliff is an experimental paradigm in which infants crawl along a board covered with patterned material placed upon a large sheet of thick glass. To one side of the board, the shallow side, the patterned material is laid directly under the glass. On the other side, the deep side, the material is spread on the floor below the glass, giving the impression of an abrupt drop. Gibson and Walk found that infants would crawl away from the board across the shallow side to their mother, but very rarely across the deep side to them, implying an innate perception of potentially dangerous sudden drops. In Sorce et al.'s (1985) adaptation of the procedure, the mothers of infants (aged 12 months) stood at the far end of the apparent drop and were instructed to show facial expressions of fear, happiness, interest or anger, without using sounds or gestures. None of the infants who saw their mother display a fearful face crossed the cliff, whereas 14 of the 19 who saw their mother's happy face did cross, demonstrating that an infant's behavior in an ambiguous situation could be influenced by their mother's facial expression. In a further adaptation of this experiment, Hornik, Risenhoover and Gunnar (1987) showed that infants played less with toys toward which their mothers had shown negative facial expressions, and effects were still present after an 8 min interval. Mumme, Fernald and Herrera (1996) also discovered similar effects, but interestingly mothers' faces alone were not found to be nearly as effective as when they were also allowed to give vocal signals. Gerull and Rapee (2002) adapted the social referencing methodology to directly investigate the observational learning of fear in toddlers (aged 15–20 months). Children were shown one of two fear-relevant stimuli (a rubber snake or a rubber spider) while their mothers verbally expressed their feelings about the stimuli and displayed one of two facial expressions: a negative (fearful/ disgusted) face; or a positive (happy/encouraging) face. After two short breaks the infants were shown the toys a second and third time, but each time mothers now presented a neutral, expressionless face. To establish whether modeling had occurred, two elements of the toddler's behavior were rated: affective response and toy-approach/avoidance behavior, during the modeling stage (mother showing emotion), after 1 min (mother's expression neutral), and again after 10 min (mother's expression neutral again). Increased fear expression and stimulus avoidance was observed in infants after they observed their mothers expressing a negative

1260

C. Askew, A.P. Field / Clinical Psychology Review 28 (2008) 1249–1265

face toward the stimulus, and was still present 10 min later. This finding has also been replicated using fear-irrelevant as well as fear-relevant stimuli; however, although fear and avoidance were still observed after 1 min, they were no longer present after 10 min for either stimulus type (Dubi et al., 2008). These are convincing demonstrations of infant–mother modeling. Changes in two fear-related measures of behavior, fear expression and stimulus avoidance, were observed after infants had observed a stimulus together with negative emotional expressions. The fact that in Gerull and Rapee's (2002) study similar changes in behavior and expression were observed 10 min later suggests that learning took place, and not merely direct imitation. The procedure made methodological advances in respect to the human vicarious fear learning literature in that it used a prospective experimental manipulation with a normal sample of children. However, there are also several methodological issues that limit interpretation of the findings. The magnitude of changes in avoidant behavior and affective response would have been clearer if there had also been baseline (pre-learning) measures with which to compare post-learning measures. Further, the lack of a control condition meant that the direction of the effect is unclear. Scores for negative modeling were compared with scores for positive modeling, but not with a no-modeling group, so it is not entirely certain that behavior changed due to negative modeling; an alternative explanation is that children in fact became less avoidant and fearful of the stimuli due to positive modeling. Recent social referencing-type studies have used a control condition. De Rosnay, Cooper, Tsigaras and Murray (2006) demonstrated that infants (aged 12–14 months) were more fearful with strangers after observing their mothers acting in a socially anxious manner with a stranger compared to when they interacted normally. Avoidance levels were also moderated greatly by the fear temperament of the child, with high fearful infants behaving in a more avoidant manner following socially anxious modeling than low-fearful infants. The mechanisms underpinning the effect were not directly investigated, but the use of a control condition does indicate that infant fear and avoidance were the result of the socially anxious behavior of their mothers. When infants interact with a stranger, mothers with social phobia show more signs of anxiety, and less encouragement of child interaction, than control mothers (Murray, Cooper, Creswell, Schofield, & Sack, 2007). When tested 4 months later, the children of these socially anxious mothers had become more avoidant of the stranger compared to infants of control mothers. Also, Egliston and Rapee (2007) recently extended Gerull and Rapee's (2002) methodology, using pre-modeling baseline measures to investigate protective factors in vicarious learning. Prior to negative modeling by the experimenter, infants (aged 12–21 months) experienced one of three experimental conditions: maternal positive modeling with the fear-relevant stimulus; the stimulus-alone without modeling; or a no-stimulus or modeling control condition. Positive maternal modeling, but not experience of the stimulus alone was found to prevent the acquisition of fear during negative modeling, and increased positive affect toward the stimulus was still found to be present after 20 min. Though fear responses for the control group increased significantly after negative modeling, they did not endure over the same time period, which is surprising given that this group underwent a similar procedure to infants in Gerull and Rapee's (2002) study. However, this may have been because in this study the experimenter, and not the child's mother, acted as the negative model; also the time until follow-up was longer than in the earlier study. Egliston and Rapee's (2007) study essentially replicated Mineka and Cook's (1986) finding demonstrating that positive modeling could prevent fear acquisition in subsequent observational learning trials with rhesus monkeys. One difference between the two studies was that in Egliston and Rapee's experiment positive modeling was conducted by mothers, but later negative modeling by the experimenter. It is possible that maternal modeling may be more potent than modeling by a stranger and this may have contributed to the strength of the inhibitive effect. One noteworthy finding was that experience of the stimulus alone did not prevent the effects of subsequent negative modeling. This is interesting because if vicarious learning is a form of associative learning then we would expect neutral experience with a stimulus to inhibit future learning via latent inhibition. This may, as the authors suggest, be due to the young age of the participants or the limited number of pre-exposure trials, but it is also worth noting that although Mineka and Cook found some (nonsignificant) indication of latent inhibition effects, only positive modeling significantly prevented fear learning. This does not mean that CS–US associations are not formed during vicarious learning, but does suggest either that latent inhibition is more difficult to demonstrate in vicarious learning, or that for some reason it is not a feature of this type of learning. 5.2. Vicarious learning in children Field, Argyris, and Knowles (2001) developed a prospective paradigm to directly examine the effects of Rachman's indirect pathways on 7–9 years old children, a key age period for the onset of animal phobias (Öst, 1987; Field & Davey, 2001). Two groups of children watched two 30 s videos showing an adult female either act fearful and avoidant or happy with two monster dolls. A questionnaire was used to measure children's self-reported fear beliefs for the animals (i.e. how children would feel about having contact with the animals and whether or not they believed they might be hurt by them). Although a small increase in children's fear beliefs, measured by questionnaire before and after the videos, was detected for the monster the model was afraid of, there was no significant change in children's fear beliefs. In contrast, in a further two groups of children who received verbal information about the dolls, fear beliefs for dolls increased significantly for children who heard negative threat information, and decreased for children who heard positive information. This effect of threat information has been replicated many times using animal stimuli (Field, 2006b; Field & Lawson, 2003), interacts with temperament (Field, 2006b), and creates attentional bias (Field, 2006b,c). Field and colleagues suggested that the videos in the vicarious learning conditions may not have produced comparable changes in fear beliefs to verbal information because they did not convey the relevant information as effectively. Another explanation could be that vicarious learning is an effective pathway to fear only for fear-relevant stimuli and not for imaginary monsters. Studies with rhesus monkeys (Cook and Mineka, 1989) support this explanation. However, studies in infants

C. Askew, A.P. Field / Clinical Psychology Review 28 (2008) 1249–1265

1261

(Dubi et al., 2008), and children (Askew & Field, 2007) contradict this explanation. Askew and Field (2007) showed that fear-relevant stimuli are not required for vicarious learning to occur. Children (aged 7–9 years) were presented with images of three novel Australian marsupials (the Quoll, Quokka, and Cuscus) together with counterbalanced images of either scared, happy or no faces (control). As in the earlier experiments, fear beliefs were measured by questionnaire before and after the manipulation. Children's fear beliefs increased significantly for animals seen with scared faces compared to animals seen with no faces, and remained higher at follow-up 1 week later. Moreover, increased fear beliefs for scared-paired animals were also detected indirectly using an affective priming task, ruling out a demand characteristics explanation, and were still present at follow-up 3 months later. Finally, a behavioral avoidance task demonstrated that, in addition to increases in fear beliefs, children were also slower to approach an animal they had previously seen together with scared faces. The use of pre-learning baseline measures and a control group indicated that changes in fear cognitions and behavior could only be due to the vicarious learning manipulation. The procedure showed that children can acquire fear beliefs and avoidance behavior in a fully controlled vicarious learning episode in the laboratory. Moreover, the comparison of animal-face pairings with an unpaired control animal indicated that vicarious learning is a form of associative learning in which the animal is a CS and the face a US. However, it did not appear that a particular animal image (CS) had simply become associated with a particular face image (US): Askew and Field used three versions of each of the three CSs paired randomly with 10 versions of each US-type (happy or scared faces), suggesting that associations had been formed between a conceptual representation of each animal and a fear-related concept representation evoked by the scared faces. A further interesting finding from Askew and Field's (2007) study was that the procedure did not appear to require the US to be a biologically significant aversive stimulus: children reported that the face USs used did not make them feel scared. Thus it appeared sufficient for the face USs merely to convey fear-relevant information, without producing a fear response. In contrast, monkeys have been found to exhibit distress during vicarious fear learning (Mineka & Cook, 1993) and adults often show galvanic skin responses during learning (e.g. Berger, 1962). Direct comparison with these studies may not be appropriate though, because phobia-like fears were not created, and nor were measures of physiological responses taken. As we have mentioned before, it is unlikely that pathways to fear work in isolation (Mineka & Zinbarg, 2006) and evidence from selfreport studies appears to suggest that pathways combine (e.g. Merckelbach et al.,1989; Muris, 2007). Askew, Kessock-Philip, and Field (in press) used Askew and Field's paradigm to investigate the interactive effects of indirect pathways by presenting verbal information before, during, and after vicarious learning. In the first part of the study children were given positive, negative, or no information about the animals before vicarious learning. Davey (1997) suggested that verbal threat information about a CS can create expectancies about the outcome (the US) of an encounter with the CS, which in turn will enhance learning of the CS–US relationship during a fear-related learning episode with the CS. It is already well-established that threat information can increase children's fear beliefs for novel animals (e.g. Field & Lawson, 2003), and these beliefs have been shown to mediate the effect of direct fear conditioning experiences in children (Field & Storksen-Coulson, 2007). It, therefore, seems likely that verbal information will also enhance subsequent negative vicarious learning for animals. Indeed a significant interaction between levels of baseline fear beliefs and vicarious learning was indicated by Askew et al.'s study: higher initial fear beliefs led to greater subsequent changes in fear beliefs during negative vicarious learning. In contrast, verbal information about the USs given during (in the form of happy and scared vocalizations by the pictured individuals) or after (the pictured persons stating that they had felt more or less scared than they appear in the pictures) vicarious learning did not significantly interact with the vicarious learning manipulation. This last finding is particularly surprising because if CS–US associations are formed during vicarious learning we would expect subsequent threat-related information about the face (US) to increase the fear response to an animal (CS) it is associated with. The effects of US revaluation are well-reported in the associative learning literature (Davey, 1989; Rescorla, 1974), and are discussed in more detail below. However, the experimenters did not establish if the threatsignificance of the US had been successfully inflated and it may simply be the case that a more potent US revaluation procedure is needed. This work is clearly in its infancy, but it does show that mild vicarious learning experiences are sufficient to create relatively long term subjective reports of fear (Lang's language behavior system) and short term avoidance (Lang's behavioral avoidance response system). There is also the first tentative evidence of interactions between the pathways. However, many issues remain to be researched. First, we do not yet know if vicarious learning causes physiological changes (Lang's final response system). Also, we do not know the knock on effect of vicarious learning on the other pathways to fear. Also, trait anxiety is known to moderate the effect of other pathways to fear (e.g. Field, 2006b) and these individual characteristics are not well-understood in relation to vicarious learning. 6. Theoretical and clinical implications 6.1. The mechanisms of vicarious learning There is good reason to believe that, irrespective of how they were originally acquired, all fears and phobias may be understood and conceptualized in terms of CS–US associations and the rules that govern them (Davey, 2002, Field, 2006a). Field (2006a) argues that informational learning is likely to be a form of associative learning in which a stimulus (CS) such as a novel animal becomes associated with negative information (US). The majority of authors have suggested that vicarious learning is a form of conditioning (e.g. Berger, 1962; Bandura, 1969; Hygge, 1976; Mineka & Cook, 1993), or that at the very least is functionally and procedurally similar enough to be considered within the same theoretical framework as associative learning (Davey, 1992; Field, 2006a). The general consensus of experimental research is that during vicarious learning the model's anxious response acts as the observer's US. The contiguous presence of this US with a neutral stimulus (CS) leads the observer to form a CS–US association, so that the stimulus subsequently evokes a conditioned fear response (CR) when it is encountered on its own. Implicit in this viewpoint has been that the model's response behavior (i.e. the observer's US) must evoke a fearful or anxious reaction (UR) in the observer: the

1262

C. Askew, A.P. Field / Clinical Psychology Review 28 (2008) 1249–1265

experience of seeing someone react fearfully to a stimulus needs to make an observer feel anxious or scared themselves for vicarious learning to occur. There is persuasive evidence that CS–US associations are formed during vicarious learning episodes involving fear-evoking USs; this is best demonstrated in the adult and rhesus monkey literatures, in which changes in physiological measures (e.g. Berger, 1962) or distress (Mineka & Cook's, 1993) were typically observed during modeling. However, changes in fear cognitions (Askew and Field, 2007) and avoidance behavior (Askew and Field, 2007; De Rosnay et al., 2006; Gerull & Rapee, 2002) in young infants and children have also been demonstrated using what appear to be less anxietyevoking vicarious learning episodes. Askew and Field's research directly investigated the mechanisms underpinning vicarious learning in children, demonstrating that it is a form of associative learning. But children in Askew and Field's experiment reported that the USs (faces) used did not make them feel scared (although the measure used to ascertain this was of unknown validity), so USs appeared to convey fear-related information, but did not need to evoke a fear response. In many ways this appears to be most similar to Hygge and Öhman's (1978) experiment using innocuous USs, though comparisons with the adult or monkey experimental literatures may not be reasonable given that neither physiological fear responses nor intense and persistent phobialike fears were investigated in the child literature. The relatively innocuous nature of the USs used with children along with the young age of infants in some of the studies may explain how individuals acquire fear-related avoidance behaviours without memory for a traumatic event: A series of relatively mild vicarious learning episodes might be less memorable for a child than a single traumatic incident but lead nonetheless to the development of a fear. Whilst changes in fear cognitions and avoidance were demonstrated, these are likely to be mild in comparison with those reported in adult and monkey experiments. However, more intense fear responses are likely to occur during a “real-world” event (e.g. a parent reacting fearfully to a spider) because of the increased relation of the model to the child, the higher intensity of the experience and level of threat, and the greater richness of information provided (e.g. movement and sound). Important though is that even milder vicarious events appear to lead to the formation of CS–US associations. This is unsurprising because contemporary conditioning research suggests that associations can be formed between a CS and a US without a UR being evoked by the US during the learning event (Field, 2006a). Given learning is associative, there are several ways in which more intense fear may subsequently develop after even relatively mild vicarious learning events. One means is via US revaluation (Rescorla, 1974): If the aversiveness of a US is increased at a later point in time, it can increase the fear-related response to a CS it is associated with. An example is a study by White and Davey (1989) in which participants initially experienced a stimulus (CS) together with an innocuous tone (US). Next the aversiveness of the tone was inflated by increasing its volume, but the CS was not presented again with the tone. However, participants showed increased skin conductance levels to the CS when it was later presented on its own, demonstrating that innocuous CS–US associations in humans can become aversive by merely inflating the aversiveness of the US. Important for vicarious learning is that a single vicarious learning event may only have to cause an observer to form an association between a representation of a stimulus (CS) and an observed person's anxious reaction to it (US), without evoking a fear response (UR) in the observer. If the anxious reaction of the model is subsequently revalued as more threatening or significant at a later point in time, the aversiveness of the stimulus it is associated with will increase in magnitude. However, whilst Askew et al. (in press) demonstrated the vicarious formation of CS–US associations in their study, initial attempts to revalue the US using verbal information about them did not prove to significantly influence fear cognitions for the CS. A second way in which even relatively innocuous vicarious learning events may aid the development of more intense fear is via the creation of outcome expectancies. Prior expectancies about the negative outcome (US) of a learning event with a CS assist learning of CS–US associations in a subsequent aversive conditioning episode (Davey, 1997; Field & Davey, 2001). Negative vicarious learning has been shown to increase children's fear beliefs for a stimulus (Askew & Field, 2007) and this is likely in turn to create negative expectancies that enhance future fear learning for the stimulus. This is one means by which Rachman's pathways are likely to interact: Each successive change in fear beliefs for a stimulus created by information (Field & Lawson, 2003) or vicarious learning may assist learning in the next direct or indirect aversive encounter with the stimulus. Thus viewed in terms of current knowledge about the characteristics of associative learning, it is likely that aversive vicarious learning involving both fearevoking and non-fear-evoking USs can contribute to the development of fears. 6.2. Implications for prevention and treatment If vicarious learning is a form of associative learning then this has important implications for treatment and prevention. Just as US inflation can increase a fear response, prevention of inflation and US devaluation should prevent fears being learnt. For example, if a child has witnessed a parent acting fearfully (US) with a stimulus the parent might reassure the child that they are actually fine, or a different relative might demonstrate that they are not fearful of the stimulus. Furthermore, given that we know that CS–US associations are formed during vicarious learning, prevention or treatment measures could aim to weaken the CS–US contingencies by exposing an individual to positive learning trials involving the stimulus. This might take the form of positive information and modeling with the stimulus (such as playfully engaging with a dog after a child has witnessed someone acting fearfully with it) and eventually lead to encouraging the individual to have direct positive contact with it. This is important even if no immediate signs of anxiety present themselves because even apparently mild CS–US associations have the potential to become traumatic if the US is negatively revalued at a later date. Prevention could be via processes related to latent inhibition and evidence suggests that positive modeling inhibits an infant's fear acquisition during a future aversive vicarious learning event (Egliston and Rapee, 2007). However, many clinically relevant features of vicarious learning have yet to be tested in the laboratory. Mineka and colleagues ‘latent inhibition’ effects need to be demonstrated in children. In terms of treatment, it would also be useful to see the

C. Askew, A.P. Field / Clinical Psychology Review 28 (2008) 1249–1265

1263

effect of extinction (exposure to the CS in the absence of fear reactions) on vicariously acquired fear associations. Also, Askew et al. (in press) failed to devalue vicariously acquired fear associations using verbal information and, therapeutically, research to explain this failure is crucial. Important is that fears that have developed via vicarious learning can be understood in terms of CS–US mechanisms, potentially giving therapists, parents and patients a framework in which to understand and make predictions about the acquisition, development and treatment of fear. Finally, although treatment was not directly investigated in the reviewed studies it is worth noting that modeling techniques have been used for some time to treat fears and phobias (e.g. Bandura, 1969; Lindsay & Powell, 1994). 7. Summary Interest in vicarious learning grew out of dissatisfaction with traditional conditioning theories of fear acquisition. Whilst current knowledge about conditioning means that many criticisms of conditioning theory are now outdated (Davey, 1997; Field & Davey, 2001), vicarious learning remains likely to be an important route to fear, and has been investigated by means of self-report studies and laboratory experiments involving adults, monkeys and children. Whilst the methodology has sometimes been criticized, self-report studies nonetheless suggest that vicarious learning plays a role in the development of many individuals' fears, though it is clear that experiencing an aversive vicarious learning episode is not in itself sufficient to predict whether an individual will develop a fear. Early experiments with adults also support the vicarious learning of fear, demonstrating that physiological fear responses can be acquired by observing others in aversive conditioning procedures. What is unclear from these studies is whether the learnt responses are lasting in the way that we would expect for fears acquired outside of the laboratory. However, persistent phobia-like fears created in monkeys give a strong indicator that vicarious learning is a viable route to fear. More recently, researchers have also turned their attention to children, demonstrating that fear-related cognitions and avoidance behavior can be vicariously learnt at an age when fears are likely to develop, and in the case of cognitions, persist for several months. Taken as a whole, research has demonstrated that vicarious learning can lead to changes in all three of Lang's (1968) fear response systems. Moreover, it indicates that vicarious learning is a form of associative learning, leading to further implications for how fears may develop over time (US revaluation), how indirect and direct pathways might interact (expectancy evaluations), and how fears might be prevented (positive modeling, latent inhibition, US devaluation). Suggestions for future work could include expanding on the emerging child research, examining further whether vicarious learning shares common characteristics of associative learning. This could potentially have important implications not only for theories of fear development, but also when applied to childhood prevention programs. In addition to exploring the preventative effects of positive modeling further, and the unresolved issues surrounding latent inhibition and US revaluation, features such as vicarious counter-conditioning could be investigated for their potential use in the treatment of childhood disorders.

References Askew, C., & Field, A. P. (2007). Vicarious learning and the development of fears during childhood. Behaviour Research & Therapy, 45, 2616−2627. Askew, C., Kessock-Philip, H., & Field, A. P., (in press). Interactions between the indirect pathways to fear in children: What happens when verbal threat information and vicarious learning combine? Behavioural and Cognitive Psychotherapy. Bandura, A. (1969). Principles of behavior modification. New York: Holt, Rineheart and Winston, Inc. Bandura, A., & Rosenthal, T. L. (1966). Vicarious classical conditioning as a function of arousal level. Journal of Personality and Social Psychology, 3, 54−62. Bandura, A., Ross, D., & Ross, S. A. (1961). Transmission of aggression through imitation of aggressive models. Journal of Abnormal and Social Psychology, 63, 575−582. Berger, S. M. (1962). Conditioning through vicarious instigation. Psychological Review, 69, 450−466. Brown, I. (1974). Effects of perceived similarity on vicarious emotional conditioning. Behaviour Research & Therapy, 12, 165−173. Cartwright-Hatton, S., McNicol, K., & Doubleday, E. (2006). Anxiety in a neglected population: Prevalence of anxiety disorders in pre-adolescent children. Clinical Psychology Review, 26, 817−833. Cook, M., & Mineka, S. (1987). Second-order conditioning and overshadowing in the observational conditioning of fear in monkeys. Behaviour Research & Therapy, 25, 349−364. Cook, M., & Mineka, S. (1989). Observational conditioning of fear to fear-relevant versus fear-irrelevant stimuli in rhesus monkeys. Journal of Abnormal Psychology, 98, 448−459. Cook, M., & Mineka, S. (1990). Selective associations in the observational conditioning of fear in rhesus monkeys. Journal of Experimental Psychology: Animal Behavior Processes, 16, 372−389. Cook, M., Mineka, S., Wolkenstein, B., & Laitsch, K. (1985). Observational conditioning of snake fear in unrelated rhesus monkeys. Journal of Abnormal Psychology, 94, 591−610. Craig, K. D., & Lowery, H. J. (1969). Heart-rate components of conditioned vicarious autonomic responses. Journal of Personality and Social Psychology, 11, 381−387. Davey, G. C. L. (1989). UCS revaluation and conditioning models of acquired fears. Behaviour Research and Therapy, 27, 521−528. Davey, G. C. L. (1992). Classical conditioning and the acquisition of human fears and phobias: A review and synthesis of the literature. Advances in Behavior Research & Therapy, 14, 29−66. Davey, G. C. L. (1995). Preparedness and phobias: Specific evolved associations or a generalized expectancy bias? Behavioral and Brain Sciences, 18, 289−325. Davey, G. C. L. (1997). Conditioning model of phobias. In G. C. L. Davey (Ed.), Phobias: A handbook of theory and research and treatment. Chichester: Wiley. Davey, G. C. L. (2002). ‘Non-specific’ rather than ‘nonassociative’ pathways to phobias: A commentary on Poulton and Menzies. Behaviour Research and Therapy, 40, 151−158. Del Russo, J. E. (1975). Observational learning of discriminative avoidance in hooded rats. Animal Learning & Behavior, 3, 76−80. De Rosnay, M., Cooper, P. J., Tsigaras, N., & Murray, L. (2006). Transmission of social anxiety from mother to infant: An experimental study using a social referencing paradigm. Behaviour Research and Therapy, 44, 1165−1175. Di Nardo, P. A., Guzy, L. T., Jenkins, J. A., Bak, R. M., Tomasi, S. F., & Copland, M. (1988). Etiology and maintenance of dog fears. Behaviour Research and Therapy, 26, 241−244. Doogan, S., & Thomas, G. V. (1992). Origins of fear of dogs in adults and children: The role of conditioning processes and prior familiarity with dogs. Behavior Research and Therapy, 30, 387−394.

1264

C. Askew, A.P. Field / Clinical Psychology Review 28 (2008) 1249–1265

Dubi, K., Rapee, R. M., Emerton, J., & Schniering, C. (2008). Maternal modeling and the acquisition of fear and avoidance in toddlers: Influence of stimulus preparedness and child temperament. Journal of Abnormal Child Psychology, 36, 499–512. Egliston, K. A., & Rapee, R. M. (2007). Inhibition of fear acquisition in toddlers following positive modeling by their mothers. Behaviour Research and Therapy, 45, 1871−1882. Ehlers, A., Hofmann, S. G., Herda, C. A., & Roth, W. T. (1994). Clinical characteristics of driving phobia. Journal of Anxiety Disorders, 8, 323−339. Feinman, S. (1982). Social referencing in infancy. Merill-Palmer Quarterly, 28, 445−470. Field, A. P. (2006). Is conditioning theory a useful framework for studying the development of phobias. Clinical Psychology Review, 26, 857−875. Field, A. P. (2006). The behavioral inhibition system and the verbal information pathway to children's fears. Journal of Abnormal Psychology, 115, 742−752. Field, A. P. (2006). Watch out for the beast: Fear information and attentional bias in children. Journal of Clinical Child and Adolescent Psychology, 35, 337−345. Field, A. P., Argyris, N. G., & Knowles, K. A. (2001). Who’s afraid of the big bad wolf: a prospective paradigm to test Rachman's indirect pathways in children. Behaviour Research and Therapy, 39, 1259−1276. Field, A. P., & Davey, G. C. L. (2001). Conditioning models of childhood anxiety. In W. K. Silverman & P. A. Treffers (Eds.), Anxiety disorders in children and adolescents: Research, assessment and intervention. Cambridge: Cambridge University Press. Field, A. P., & Lawson, J. (2003). Fear information and the development of fears during childhood: Effects on implicit fear responses and behavioral avoidance. Behaviour Research and Therapy, 41, 1277−1293. Field, A. P., & Storksen-Coulson, A. (2007). The interaction of pathways to fear in childhood anxiety: A preliminary study. Behaviour Research and Therapy, 45, 3051−3059. Forsyth, J. P., & Chorpita, B. F. (1997). Unearthing the nonassociative origins of fears and phobias: A rejoinder. Journal of Behavior Therapy and Experimental Psychiatry, 28, 297−305. Gerull, F. C., & Rapee, R. M. (2002). Mother knows best: Effects of maternal modeling on the acquisition of fear and avoidance behaviour in toddlers. Behaviour Research and Therapy, 40, 279−287. Gibson, E. J., & Walk, R. D. (1960). The visual cliff”. Scientific American, 202(4), 64−71. Globisch, J., Hamm, A. O., Esteves, F., & Öhman, A. (1999). Fear appears fast: Temporal course of startle reflex potentiation in animal fearful subjects. Psychophysiology, 36, 66−75. Graham, J., & Gaffan, E. A. (1997). Fear of water in children and adults: Etiology and familial effects. Behaviour Research and Therapy, 35, 91−108. Green, G., & Osborne, J. G. (1985). Does vicarious instigation provide support for observational learning theories? A critical review. Psychological Bulletin, 97, 3−17. Hekmat, H. (1987). Origins and development of human fear reactions. Journal of Anxiety Disorders, 1, 197−218. Hofmann, S. G., Ehlers, A., & Roth, W. T. (1995). Conditioning theory a model for the etiology of public speaking anxiety? Behaviour Research and Therapy, 33, 567−571. Hornik, R., Risenhoover, N., & Gunnar, M. R. (1987). The effect of maternal positive, neutral, and negative affective communications on infant responses to new toys. Child Development, 58, 937−944. Hygge, S. (1976). Information about the model's unconditioned stimulus and response in vicarious classical conditioning. Journal of Personality and Social Psychology, 33, 764−771. Hygge, S., & Öhman, A. (1978). Modeling processes in the acquisition of fears: Vicarious electrodermal conditioning to fear-relevant stimuli. Journal of Personality and Social Psychology, 36, 271−279. de Jongh, A., Muris, P., Ter Horst, G., & Duyx, M. P. M. A. (1995). Acquisition and maintenance of dental anxiety: The role of conditioning experiences and cognitive factors. Behaviour Research and Therapy, 33, 205−210. Joslin, J., Fletcher, H., & Emlen, J. (1964). A comparison of the responses to snakes of lab- and wild-reared rhesus monkeys. Animal Behavior, 12, 348−352. Kessler, R. C., McGonagle, K. A., Zhao, S., Nelson, C. B., Hughes, M., Eshleman, S., et al. (1994). Lifetime and 12-month prevalence of DSM-III-R psychiatric disorders in the United States: Results from the National Comorbidity Study. Archive of General Psychiatry, 51, 8−19. King, N. J., Clowes-Hollins, V., & Ollendick, T. H. (1997). The etiology of childhood dog phobia. Behaviour Research and Therapy, 35, 77. Kheriaty, E., Kleinknecht, R. A., & Hyman, I. E., Jr. (1999). Recall and validation of Phobia Origins as a function of a structured interview versus the Phobia Origins Questionnaire. Behavior Modification, 23, 61−78. Kirkby, K. C., Menzies, R. G., Daniels, B. A., & Smith, K. L. (1995). Aetiology of spider phobia: Classificatory differences between two origins instruments. Behaviour Research and Therapy, 33, 955−958. Kleinknecht, R. A. (1994). Acquisition of blood, injury, and needle fears and phobias. Behaviour Research and Therapy, 32, 817−823. Kleinknecht, R. A. (2002). Comments on: non-associative fear acquisition: A review of the evidence from retrospective and longitudinal research. Behaviour Research and Therapy, 40, 159−163. Kohn, B. (1976). Observational and discrimination learning in the rat: Effects of stimulus substitution. Learning & Motivation, 7, 303−312. Kravetz, D. F. (1974). Heart rate as a minimal cue for the occurrence of vicarious classical conditioning. Journal of Personality and Social Psychology, 29, 125−131. Lang, P. J. (1968). Fear reduction and fear behavior: Problems in treating a construct. In J. M. Schlien (Ed.), Research in psychotherapy, Vol. 3 (pp. 90−103) . Washington, DC: American Psychological Association. Lindsay, S. J. E., & Powell, G. E. (1994). The handbook of clinical adult psychology (second edition). London: Routledge. Lubow, R. E. (1989). Latent inhibition and conditioned attention theory. Cambridge: CUP. Mason, J. R., & Reidinger, R. F. (1982). Observational learning of food aversions in red-winged blackbirds (Agelaius phoeniceus). The Auk, 9, 548−554. McNally, R. J., & Steketee, G. S. (1985). The etiology and maintenance of severe animal phobias. Behaviour Research and Therapy, 23, 431−435. Menzies, R. G. (1996). The origins of specific phobias in a mixed clinical sample: Classificatory differences between two origins instruments. Journal of Anxiety Disorders, 10, 347−354. Menzies, R. G., & Clarke, J. C. (1993). The etiology of fear of heights and its relationship to severity and individual response patterns. Behaviour Research and Therapy, 31, 355−365. Menzies, R. G., & Clarke, J. C. (1993). The etiology of childhood water phobia. Behaviour Research and Therapy, 31, 499−501. Menzies, R. G., & Clarke, J. C. (1994). Retrospective studies of the origins of phobias: A review. Anxiety, Stress and Coping, 7, 305−318. Menzies, R. G., & Clarke, J. C. (1995). The etiology of acrophobia and its relationship to severity and individual response patterns. Behaviour Research and Therapy, 33, 795−803. Menzies, R. G., & Clarke, J. C. (1995). The etiology of phobias: A non-associative account. Clinical Psychology Review, 15, 23−48. Menzies, R. G., Kirkby, K., & Harris, L. M. (1998). The convergent validity of the Phobia Origins Questionnaire: A review of the evidence. Behaviour Research and Therapy, 36, 1081−1089. Merckelbach, H., Arntz, A., Arrindell, W. A., & De Jong, P. J. (1992). Pathways to spider phobia. Behaviour Research and Therapy, 30, 543−546. Merckelbach, H., Muris, P., & Schouten, E. (1996). Pathways to fear in spider phobic children. Behaviour Research and Therapy, 34, 935−938. Merckelbach, H., de Ruiter, C., van den Hout, M. A., & Hoekstra, R. (1989). Conditioning experiences and phobias. Behaviour Research and Therapy, 27, 657−662. Mineka, S., & Cook, M. (1986). Immunization against the observational conditioning of snake fear in rhesus monkeys. Journal of Abnormal Psychology, 95, 307−318. Mineka, S., & Cook, M. (1993). Mechanisms involved in the observational conditioning of fear. Journal of Experimental Psychology, 122, 23−38. Mineka, S., Davidson, M., Cook, M., & Keir, R. (1984). Observational conditioning of snake fear in rhesus monkeys. Journal of Abnormal Psychology, 93, 355−372. Mineka, S., Keir, R., & Price, V. (1980). Fear of snakes in wild- and lab-reared rhesus monkeys (Macaca mulatta). Animal Learning and Behavior, 8, 653−663. Mineka, S., & Öhman, A. (2002). Born to fear: Non-associative vs. associative factors in the etiology of phobias. Behaviour Research and Therapy, 40, 173−184. Mineka, S., & Zinbarg, R. (1996). Conditioning and ethological models of anxiety disorders: Stress-in-dynamic-context anxiety models. In D. Hope (Ed.), Perspectives on anxiety, panic, and fear (43rd Annual Nebraska Symposium on Motivation). University of Nebraska Press: Lincoln. Mineka, S., & Zinbarg, R. (2006). A contemporary learning theory perspective on the etiology of anxiety disorders: It's not what you thought it was. American Psychologist, 61, 10−26. Mumme, D. L., Fernald, A., & Herrera, C. (1996). Infant's responses to facial and vocal emotional signals in a social referencing paradigm. Child Development, 67, 3219−3237.

C. Askew, A.P. Field / Clinical Psychology Review 28 (2008) 1249–1265

1265

Muris, P. (2007). Normal and abnormal fear and anxiety in children: What was really wrong with Little Hans? Oxford: Elsevier Science. Muris, P., & Merckelbach, H. (2001). The etiology of childhood specific phobias: A multifactorial model. In M. W. Vasey & M. Dadds (Eds.), The developmental psychopathology of anxiety. New York: Oxford University Press. Muris, P., Merckelbach, H., & Collaris, R. (1997). Common childhood fears and their origins. Behaviour Research and Therapy, 35, 929−937. Muris, P., Steerneman, P., Merckelbach, H., & Meesters, C. (1996). Parental modeling and fearfulness in middle childhood. Behaviour Research and Therapy, 34, 265−268. Murray, E. J., & Foote, F. (1979). The origins of fear of snakes. Behaviour Research and Therapy, 12, 489−493. Murray, L., Cooper, P., Creswell, C., Schofield, E., & Sack, C. (2007). The effects of maternal social phobia on mother–infant interactions and infant social responsiveness. Journal of Child Psychology and Psychiatry, 48(1), 45−52. Öhman, A., & Mineka, S. (2001). Fears, phobias, and preparedness: Toward an evolved module of fear and fear learning. Psychological Review, 108, 483−522. Ollendick, T. H., & King, N. J. (1991). Origins of childhood fears: An evaluation of Rachman's theory of fear acquisition. Behaviour Research and Therapy, 29, 117−123. Olsson, A., & Phelps, E. A. (2004). Learned fear of “unseen” faces after Pavlovian, observational, and instructed fear. Psychological Science, 15, 822−828. Olsson, A., & Phelps, E. A. (2007). Social learning of fear. Nature Neuroscience, 10, 1095−1102. Öst, L. G. (1985). Ways of acquiring phobias and uutcome of behavioral treatments. Behaviour Research and Therapy, 23, 683−689. Öst, L. G. (1987). Age of onset in different phobias. Journal of Abnormal Psychology, 96, 223−229. Öst, L. G. (1991). Acquisition of blood and injection phobia and anxiety response patterns in clinical patients. Behaviour Research and Therapy, 29, 323−332. Öst, L. G., & Hugdahl, K. (1981). Acquisition of phobias and anxiety response patterns in clinical patients. Behaviour Research and Therapy, 19, 439−447. Öst, L. G., & Hugdahl, K. (1985). Acquisition of blood and dental phobia and anxiety response patterns in clinical patients. Behaviour Research and Therapy, 23, 27−34. Öst, L. G., & Treffers, P. A. (2001). Onset, course, and outcome for anxiety disorders in children. In W. K. Silverman & & P. A. Treffers (Eds.), Anxiety disorders in children and adolescents: Research, assessment and intervention. Cambridge: Cambridge University Press. Pillemer, D. B. (1998). What is remembered about early childhood events? Clinical Psychology Review, 18, 895−913. Poulton, R., & Menzies, R. G. (2002). Non-associative fear acquisition: A review of the evidence from retrospective and longitudinal research. Behaviour Research and Therapy, 40, 127−149. Rachman, S. (1968). Phobias: Their nature and control. Springfield: Thomas Books. Rachman, S. (1977). The conditioning theory of fear-acquisition: A critical examination. Behaviour Research and Therapy, 15, 375−387. Rescorla, R. A. (1974). Effect of inflation of the unconditioned stimulus value following conditioning. Journal of Comparative and Physiological Psychology, 86, 101−106. Rescorla, R. A. (1980). Pavlovian second-order conditioning: Studies in associative learning. Hillsdale: Lawrence Erlbaum. Rescorla, R. A. (1988). Pavlovian conditioning: It's not what you think it is. American Psychologist, 43, 151−160. Rimm, D. C., Janda, L. H., Lancaster, D. W., Nahl, M., & Dittmar, K. (1977). An exploratory investigation of the origin and maintenance of phobias. Behaviour Research and Therapy, 15, 231−238. Seligman, M. E. P. (1971). Phobias and preparedness. Behavior Therapy, 2, 307−320. Siddle, D. A. T., Remington, B., & Churchill, M. (1985). Effects of conditioned stimulus pre-exposure on human electrodermal conditioning. Biological Psychology, 20, 113−127. Sorce, J. F., Emde, R. N., Campos, J., & Klinnert, M. D. (1985). Maternal emotional signaling: Its effects on the visual cliff behavior of 1-year olds. Developmental Psychology, 21, 195−200. Taylor, J. E., Deane, F. P., & Podd, J. V. (1999). Stability of driving fear acquisition pathways over one year. Behaviour Research and Therapy, 37, 927−939. Vaughan, K. B., & Lanzetta, J. T. (1980). Vicarious instigation and conditioning of facial expressive and autonomic responses to a model's expressive display of pain. Journal of Personality of Social Psychology, 38, 909−923. White, K., & Davey, G. C. L. (1989). Sensory preconditioniong and UCS inflation in human fear conditioning. Behaviour Research and Therapy, 27, 161−166. Withers, R. D., & Deane, F. P. (1995). Origins of common fears: Effects on severity, anxiety responses and memories of onset. Behaviour Research and Therapy, 33, 903−915.