A study of the attentional changes accompanying orienting to different types of change stimuli

Acta Psychologica North-Holland

61 (1986)

153-166

153

A STUDY OF THE ATTENTIONAL CHANGES ACCOMPANYING ORIENTING TO DIFFERENT TYPES OF CHANGE STIMULI * Daniel T.L. SHEK ** and John A. SPINKS University

of Hong

Accepted

May

Kong,

Hong

Kong

1985

The effects of the orienting response on subsequent motor response efficiency were studied. Subjects underwent a standard habituation series of fifteen trials. On the sixteenth trial, they received one of four stimuli each of which was followed by a reaction time (RT) task: (a) same stimulus as the habituation stimulus, (b) slide of the word ‘COMING’ which subjects had been forewarned would precede the reaction time task, (c) subject’s own name, (d) innocuous change stimulus. The results showed that RT was generally slowed in the stimulus-related change conditions compared with the no change condition, indicating that orienting to a novel or significant stimulus does not result in a generalized alerting or arousal. While skin conductance and heart rate data show no difference between the various change trial conditions, digital pulse amplitude changes, particularly later in the processing of the stimulus complex, differentiated these conditions. The data elucidate the information processing changes that accompany orienting. The significance and theoretical implications of the data are discussed.

Contemporary theoretical views of the orienting response (OR) stress the intimate nature of the relationship between the OR and attentional processes (e.g., Kahneman 1973). But only recently have researchers focussed on the precise nature of the ways in which the information processing system is changed during the evocation of an OR (Spinks and Siddle 1983) and on the results of these changes. An examination of the literature ten years ago showed that very few studies had then been directed towards an investigation of this parameter of the OR * The manuscript was based upon part of a doctoral thesis submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the University of Hong Kong. Portions of the present report were presented in preliminary form at the 22nd Annual Meeting of the Society for Psychophysiological Research, Minneapolis, November, 1982. ** The first author is at present at the Dept. of Social Administration, City Polytechnic of Hong Kong. Mailing address: D.T.L. Shek, Dept. of Social Adminstration, City Polytechnic of Hong Kong, Argyle Centre, Tower II, 688, Natan Road, Kowloon, Hong Kong. OOOl-6918/86/$3.50

0 1986,

Elsevier

Science

Publishers

B.V. (North-Holland)

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(Barham and Boersma 1975). Most of the research had been directed towards an understanding of the processes underlying the elicitation, habituation and re-evocation of the OR, leaving the exact attentional nature of the OR unclear (Spinks 1980; Spinks and Siddle 1983). The lack of empirical evidence for the proposals that the functional significance of the OR is to enhance attention and information processing, is further complicated by the existence of different views of the attentional nature of the OR. There are theoretical positions which suggest that the OR is an index of ‘registration’ of information, but not of any perceptual or somatomotor activation (Pribram and McGuinness 1975; Bagshaw et al. 1965; Bagshaw and Benzies 1968). Other authors, however, maintain that the OR indicates the enhancement of perceptual processing (Sokolov 1963; Kahneman 1973; Bernstein and Taylor 1979; Teichner 1968; Siddle and Spinks 1979; Graham 1979; Koepke and Pribram 1966; Adam 1980; Jeffrey 1968) or motor performance (e.g., Lynn 1966; Germana 1968,1969). There is probably even greater ambiguity regarding the relationship between the OR and motor responding. Germana (1969) implied an important role for the OR in output mechanisms when he described the essential nature of the OR as being a ‘What’s to be done?’ rather than a ‘What is it?’ role. Sokolov’s original theoretical position in this regard was far from clear, although Lynn’s (1966) view was that one of the results of the OR was an preparatory increase in muscle tension. Similarly, Ruttkay-Nedecky (1967) saw the autonomic reaction as being important in preparing the organism for future action. However, more contemporary theories of the OR (e.g., Graham 1979) have viewed the OR as being related to more efficient and/or deeper processing of incoming information, rather than of responses. However, if the OR results in some input enhancement effects (e.g., Graham 1979), it is likely that it may also lead to a deterioration in motor performance, since there is literature suggesting an antagonistic relationship between the input and output systems (Routtenberg 1968; Graham 1979). In other words, stimulus-related ORs might inhibit ~response time by diverting the available processing capacity for input purposes. An examination of the available evidence shows equivocal effects of the OR on motor response performance. Although there is some indirect evidence showing that an accessory stimulus might facilitate motor performance (e.g., Nickerson 1973; Posner 1975; Blackman 1966),

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there are several problems related to such kind of evidence (Spinks 1977). Firstly, since most of the reaction time (RT) studies have not primarily addressed the question of motor effects of the OR, explanations of such findings have seldom been made within an OR context. Furthermore, alternative explanations are available. For example, in explaining intersensory facilitation, explanations in terms of energy summation (Nickerson 1973) or the alerting function of the accessory stimulus (John 1964) have been put forward. Secondly, since most of the studies did not record any physiological activity&he occurrence of the OR can only be inferred. Even when physiological responses have been analyzed, the data are equivocal (Blackman 1966; cf. van Olst 1971). Thirdly, most of the related studies have probably involved anticipatory (i.e., ORs elicited by stimuli which convey information concerning some future events or anticipation of informative stimulus; Graham 1979; Siddle and Spinks 1979; Spinks et al. 1984) rather than stimulus-related ORs (i.e., ORs elicited by stimuli with physical parameter changes). This distinction relates to the direction of attention, with anticipatory ORs directing attention to scanning the environment for future information (and possibly away from the evoking stimulus), whilst stimulus-related ORs direct attention to the evoking stimulus itself. Not only, therefore, is there little information available about the motor effects of stimulus-related ORs, but it could be argued that the response system changes that result from these two types of ORs might be different. For example, the information processing changes that accompany an anticipatory OR would depend upon whether identification or responding is anticipated, whilst stimulus-related ORs would presumably result in increased capacity directed towards identifying the novel stimulus, and, therefore, away from motor system enhancement. Furthermore, other authors (e.g., Kahneman 1973; Spinks and Siddle 1983) have argued that the OR concept is an umbrella concept under which a number of related, but distinguishable responses rest. There have been numerous attempts to subdivide the OR concept in this way (e.g., signal/non-signal ORs; goal-directed/stimulus-related ORs to significant/non-significant stimuli). Whilst the heuristic value of such a theoretical stance is debatable, it is possible that each type of OR may be distinguishable, not just at a stimulus level, as above, but at a functional level. The present experiment was designed to investigate whether the OR facilitates motor activity (i.e., whether processing capacity is allocated

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for output purposes). If the OR is related primarily to input facilitation functions, it was predicted that, when a motor demanding task follows orienting, additional time would be required to transfer the allocated processing capacity to the effector span, leading to a longer time to execute the motor response. If this line of reasoning is correct, it would be further expected that the more significant an orienting stimulus is, the greater would be the degree of inhibition and the longer the time required to execute a RT task, since there are views suggesting that the more significant the stimulus, the more intensive the scanning activities would be (e.g., Bernstein and Taylor 1979). A number of different types of ‘significance’ were investigated in this experiment, in order to throw some light upon this issue. An innocuous change stimulus, like those traditionally used in studies of OR habituation and recovery, was used, as were stimuli of two levels of significance, based on the distinction made by Wingard and Maltzman (1980). The first was related to long-term significance or dispositions (the subject’s name) and the second to short-term interests (specific task instructions). Finally, the experiment investigated the motor effects of different types of ORs (stimulus-related ORs and anticipatory ORs). Based on the preceding discussion, it was predicted that stimulus-related ORs would result in more deterioration of RT performance than ORs evoked in anticipation of a known motor task. The experiment involved habituating subjects to a neutral stimulus, and then looking at the effect of a change (no change in the control condition) stimulus on responding to a subsequent IS. The experimental paradigm thus conforms closely to one of the standard paradigms for eliciting and investigating ORs. Method

Ss were 48 Chinese volunteer students at the University of Hong Kong. Owing to equipment failures, eight additional Ss were used to replace eight of the original Ss, leaving a final sample of 25 males and 23 females (age range 18-24). All Ss had normal, or corrected-to-normal, vision and they had taken Chinese Language in the Hong Kong Certificate of Education Examination. They were randomly assigned to four conditions, with 12 Ss in each group. Apparatus

and recording

techniques

All visual stimuli were slides presented via a projection tachistoscope, controlled by a PDP8e laboratory computer. A S.L.E. polygraph was used to record skin resistance,

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cardiac activity and digital pulse amplitude (DPA). Na/NaCl electrodes were used for measurement of electrodermal activity together with a 0.05M NaCl paste. The electrodes were attached to the masked areas over the whorls of the fingerprints on the index and second fingers of the S’s left hand. EKG signals were obtained from a standard Lead I configuration. The signals were fed into a S.L.E. AC preamplifier, with a time constant of 0.03 sec. Digital pulse amplitude (DPA) was measured via a photocell transducer on the first phalanx of the third finger of the S’s right hand. The signals obtained were AC coupled, with a time constant of 0.03 sec. The electrodermal, EKG and DPA signals were also fed into three channels of a FM instrumentation tape recorder for later analysis. Experimental

design and stimulus

There were in all three experimental groups: Innocuous Change (IC); Long-Term Significant Change (LSC); Short-Term Significant Change (SSC) conditions, and one control group (NC: No Change condition). The experimental design employed was a repetition-change paradigm in which there were 15 repetition trials and one change trial (16th trial) for each experimental group. The stimuli presented to the Ss for the 15 repetition trials for the 4 groups were identical, being the presentation of a slide of 5 black horizontal lines on white background, The nature of the change or ‘orienting stimulus’ (OS) for the 16th trial varied for the four conditions. In the NC condition, the same slide of straight lines was presented again as the OS. The results of this group constituted the baseline by which the effects of orienting could be assessed. In the IC condition, the OS presented was a slide of tilted lines. This change was assumed to be insignificant, but to reflect the effect of novelty (innocuous change). In the LSC conditon, the OS was a slide with the Chinese name of the S printed on it. Since the S’s name is assumed to be related to ‘long-term’ significance (Wingard and Maltzman 1980), the effects of an OR evoked by such a significant stimulus could be assessed. The final condition (SSC), related to anticipatory ORs and short-term stimulus significance, employed an OS which consisted of a slide with the word ‘COMING’ printed on it. The Ss in this condition were instructed before the experiment that the encoding task would shortly follow the presentation of this slide. While the purpose of this condition was to test whether anticipatory ORs facilitated RT performance, the previous two conditions were employed to investigate the effects of different types of stimulus-related ORs on motor performance, The IS was a slide on which two identical Chinese characters were printed in the centre ( $EiJ‘ 17 ). The characters used were printed in bold characters style with 5 x 5 mm for each character. The visual angle subtended by each of the characters was approximately 1.5”. The inter-stimulus intervals varied for these stimuli randomly between 20 to 40 seconds. All stimuli were of 500-msec duration, except for the imperative stimulus (IS) presented following trial 16, the offset of which was contingent upon the S’s response. The interval between the OS of trial 16 and the IS (DT) was 500 msec. The employment of durations of 500 msec for the OS and DT was based on two grounds. Firstly, in many situations (Posner and Boies 1971; Spinks and Siddle 1983), both preparation and encoding processes are optimally facilitated around 500 msec. Secondly, there is

158 evidence paradigm 1983).

D. T.L. Shek, J.A. Spinks / OR and reaction time from earlier studies that maximal perceptual occurs when both the OS and DT durations

enhancement in this sort of are around this value (Shek

Procedure The Ss were seated in a padded chair alone in a soundproofed room in which the screen was approximately 2 m in front of the Ss. A two-way intercom enabled communication between the Ss and the experimenter. The recording and the projection equipment were housed in an adjacent room. The Ss were told that their task was to decide whether the two presented Chinese characters in the IS were physically identical or not by stating ‘yes’ or ‘no’ in Chinese after the IS had been presented. An example of the matching task was shown and a practice trial was administered. The Ss were instructed that they should respond ‘as quickly as possible’. The Ss were also instructed that besides the IS, slides of patterns would also be presented during the experiment. An example of the habituation stimulus was shown. The Ss were told that when presented with the slide of patterns, their task was merely to look at the screen. They were told that they did not have to actively remember anything or analyze these slides of patterns. The Ss in the SSC condition were further instructed that a slide with the word ‘COMING’ printed on it would immediately precede the presentation of the encoding stimulus. This slide was also shown to the Ss in this group. After the electrodes had been attached, the Ss were asked to relax. After 5 minutes, they were informed that the experiment would begin in one minute. After the 16th trial, the Ss were asked to relax. Then a white noise stimulus (l/2 set; 90 dB) was presented to the Ss, the responses to which were used for range-correction purposes. Data analysis Raw skin resistance data were transformed into conductance before calculating response amplitudes. The electrodermal reponse was defined as any artifact-free phasic change which occurred within 1 to 5 seconds following the onset of the stimulus. In order to reduce confounding of SCR magnitude measures with peripheral physiological factors (and hence increase experimental sensitivity), electrodermal responses were range-corrected (Lykken et al. 1966) using the S’s largest electrodermal responses during the experiment. Siddle et al. (1980) discussed two major problems with rangecorrection procedures, the first being a practical one of obtaining the maximal response from Ss and the second being one of interaction of treatment conditions with the response used for range-correction. The range-corrected SCR values had a mean of 0.1771 and the maximal response in all cases occurred following either the range-correction stimulus or the first stimulus, both of which were identical for all Ss. These findings thus suggest that the above problems have been minimized in this experiment. For cardiac activity, set-by-set heart rate (HR) was computed by weighting the proportions of each second taken up by each beat (e.g., Graham and Jackson 1970) for 10 post-stimulus seconds. Pre-stimulus respiratory sinus arrhythmia effects were removed using the S-A correction method suggested by Siddle and Turpin (1980). Mean DPAs were similarly calculated for each of the eight l-second periods following the stimulus onset. These were then expressed as a percentage change from the mean DPA

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during the 3 seconds preceding stimulus onset. Owing to recording artifacts due to the occurrence of the IS, DPA percentage changes were only analyzed from post-stimulus 3 to 10 seconds. In all repeated measures ANOVAs, Wilson’s (1967) suggestion was followed in which the value of epsilon was estimated at 0.5. Degrees of freedom are corrected accordingly. RT was measured as the time from the onset of the IS to the beginning of the S’s verbal response (voice-key activation of timer). Results Analysis of the SCR data of the 16th trial shows no significant differences between the various groups. Further analyses of the SCR data for the 15 repetition trials using three trial blocks (Trials 1 to 5, Trials 6 to 10, Trials 11 to 15) showed significant differences between the three trial blocks for NC (F(2/22) = 3.599, p < 0.05), IC (F(2/22) = 15.509, p < 0.05), LSC (F(2/22) = 9.483, p < 0.05), SSC (F(2/22) = 6.297, p < 0.05) and the overall (P(2/88) = 24.467, p < 0.05) conditions. Post-hoc comparisons using Duncan’s Multiple Range Test showed significant differences between Trial Blocks 1 and 3 for all the conditions, indicating the occurrence of habituation. The mean SCR magnitude for the various conditions in the repetition and change trials are presented graphically in fig. 1.

ssc LSC NC

1, 3

6

9

12

15

16 TRIAL

NUMBER

.

Fig. 1. Mean SCR magnitude for the NC, IC, LX, change trials.

and SSC conditions in the repetition and

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-1 -2

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SECONDS

Fig. 2. Mean set-by-set HR change for the NC, IC, LSC and SSC conditions following the onset of the orienting stimulus. The HR change data (fig. 2) following the 16th trial were analyzed by a polynominal trend ANOVA with seconds (post-stimulus second 1 to 10) and groups (NC, IC, SSC, LSC) as main factors. The analysis yielded a significant effect for seconds (F(5/198) = 2.71, p < O.OS), of which both the quadratic (F(1/198) = 4.94, p < 0.05), and cubic (P(1/198) = 13.88, p < 0.01) components were significant. Poststimulus HR activities for the various conditions basically showed an acceleratory limb, followed by a deceleration. There were no significant main effects for interactions involving the groups factor. DPA scores were similarly analyzed. Significant effects of seconds (F(4/154) = 22.04, p < 0.01) .with linear (F(1/154) = 125.67, p < O.OOl), quadratic (P(1/154) = 18.43,. p < 0.01) and cubic (P(1/154) = 6.57, p < 0.01) components all being significant. The DPA results are shown graphically in fig. 3. Visual inspection shows that the amount of vasoconstriction is greatest for the LSC condition as compared to the other conditions. Although no significant group effects were found in the above ANOVA, further analyses using Newman-Keuls test showed significant differences between the LSC and NC on seconds 3,4, 7, 8 and 9, between LSC and IC on seconds 3, 4, 5, 8, 9 and 10, and between LSC and SSC on seconds 3,4,7, 8,9 and 10. A one-way ANOVA for the reaction time (RT) data showed a significant effect for groups (F(3/44) = 7.10, p < 0.01). The RT data are graphically shown in fig. 4. Post-hoc comparisons using Duncan’s Multiple Range Test showed significant differences between the NC and LSC (p < 0.05) LSC and SSC (p < 0.05), and IC and SSC (p < 0.05) conditions.

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time

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change for the NC, IC, LSC and SSC conditions of the orienting stimulus.

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following

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1600

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1200

1000

800

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Fig. 4. Mean

RT to the imperative

IC

NC

ssc

stimulus

under

the NC,

LSC

IC, LSC and SSC conditions.

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Discussion The physiological data showed few significant effects for the different conditions on trial 16. This could be explained in terms of the temporal proximity of the OS and IS, the response requirements of the IS masking any differential responding to the OS. There is, of course, evidence to suggest that response requirements can modify autonomic responding (e.g., Hare 1972; Edwards and Alsip 1969). Nevertheless, there is no support in this study for the view that SCR or heart rate response (HRR) indexes the type of attentional changes that have occurred as a result of the OR. Although stimulus-related and anticipatory ORs result in different RT performance, they cannot be distinguished in terms of their accompanying electrodermal or cardiac component in this study. The accelerative HRR on trial 16 in all conditions are generally consistent with Jennings and Hall’s (1980) view that acceleration reflects the unavailability of processing capacity, or the ‘effort’ required to process the stimulus. The most likely explanation of the HR acceleration, however, is that it represents the increase in somatomotor activity required following the presentation of the IS. Although there were some interesting trends in HR which appeared to differentiate the experimental groups, none of the statistical tests showed any clear significant difference between the groups. Interestingly, the only system to differentiate the experimental groups was DPA, where the amount of constriction was greater for the LSC group than the other groups. Despite the covariation between DPA and anxiety reported by numerous authors (e.g., Kelly 1966; Bloom and Trautt 1977), the DPA response differentiating groups is probably most easily seen as a component of the OR. However, it can be seen from reference to the figure that this response occurs some 7-10 sets following onset of the OS, and it might be tentatively suggested that this is a concomitant of a reappraisal of the significance of the OS, after the immediate attentional and motor demands of the IS have passed. This interpretation would explain why there is little significant effect for the electrodermal data, since only a single response, evoked immediately following the onset of the OS, was analyzed. As has been mentioned, the HR data are probably confounded by motor response requirements, although a tendency towards the same sort of effects

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shown by the DPA data may be seen in the decelerative HR response to the LSC stimulus around 9 set post-stimulus. A number of authors (Kahneman 1973; ohman 1979; Spinks and Siddle 1983) have indicated that the OR normally evoked by a stimulus is the result of a preattentive analysis of that stimulus. It could be speculated that the late DPA response observed in this study is the result of some later, controlled processing of the stimulus, this processing following a preattentive analysis when the latter indicates that a call for extra processing is required. This ‘call’ has been related to the occurrence of the OR in Ghman’s (1979) model. The most interesting effect for the RT data was the deterioration in RT following the LSC stimulus. There was a similar trend for the RT to the IC stimulus although this effect was statistically non-significant. These results are in line with the predictions although they are somewhat contrary to the intuitive expectation that a change stimulus would generally alert the subject. In addition, there is little support in these data for those theorists who maintain that the OR results in motor facilitation (e.g., Ruttkay-Nedecky 1967). Clearly, a certain amount of clarification is required concerning the role of the OR in effecting changes in the output system. These data could be explained in terms of the direction of distribution of processing capacity during orienting. It is suggested that the following course of events might occur following a novel stimulus. First, the receptor mechanisms are enhanced, in order to increase perceptual readiness and scanning activities (Teichner 1968; Bernstein and Taylor 1979). As a result, if the IS occurs some time following the novel stimulus, additional time is required to re-allocate the processing capacity from the receptor mechanisms to the effector side. This follows from Routtenberg’s (1968) proposal that input and output processes compete for limited central processing capacity (as Kahneman’s (1973) view of undifferentiated information processing capacity), and, as a result, act in an antagonistic manner. The time required for re-allocation thus leads to an increase in RT in the stimulus-related OR (IC, LSC) conditions. According to Teichner (196Q when encountering a novel stimulus, the attentional bandwidth of a person broadens as a result of the involvement of the input system in which greater scanning activities are present. The data are consistent with this view, since Teichner also equates a wider attentional bandwidth with slower

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processing rates, slower scanning rates, and slower responses. These proposals can easily accommodate the stronger RT effects following the LX stimulus, compared with the IC stimulus. The SSC stimulus was specifically intended to produce orienting in anticipation of future information processing demands, and might therefore have been expected to facilitate RT. The most likely explanation of the non-significant effects is that the time needed to identify the stimulus, understand the relevance of the stimulus to the task in hand (which would involve memory searches), and then redistribute information processing resources appropriately, takes much longer than the normal, more reflexive, type of orienting, on which the stimulus and inter-stimulus durations of the present study were based. The concept of ‘anticipatory’ or ‘expectancy’ ORs was first proposed by Voronin and Kotlar (1962; cited in Voronin et al. 1975), and has been the subject of recent research by Spinks and Siddle (1985) and Spinks et al. (1985). At a process level, it might be suggested that either the receptor or effector mechanisms (or perhaps both) would be facilitated following such an anticipatory OR, depending on the nature of instructions. This idea of ‘functional specificity’ is not new (Israel et al. 1980), although it should be noted that, in order for it to have any heuristic value, the situations which result in particular function must be adequately specified. In summary, the present findings point to a number of important issues. There appears to be a need to dissociate the receptor and effector aspects of attention in relation to the functional significance of the OR. There is no evidence to support the view that the effector side is enhanced during orienting - indeed, the data suggest that information processing resources are pulled away from the effector side, presumably towards the receptor side, in the case of ORs where attention is directed towards the OR-eliciting stimulus. With anticipatory ORs, the situation is more complex, since it would seem likely that the attentional changes would depend upon the situational demands expected. It was noted earlier that this concept of ‘functional specificity’ is of little heuristic value in itself, and awaits more detailed investigation. Clearly, however, the data indicate that it is not sufficient to link the OR to generalized attentional changes. Neither Kahneman’s (1973) nor ohman’s (1979) model of the OR appear to be specific enough to incorporate the data from the present experiment.

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References Adam, G., 1980. Perception, consciousness, memory - reflections of a biologist. New York: Plenum Press. Bagshaw, M.H. and S. Benzies, 1968. Multiple measures of the orienting reaction and their dissociation after amygdalectomy in monkeys. Experimental Neurology 20, 175-187. Bagshaw, M.H., D.P. Kimble and K.H. Pribram, 1965. The GSR of monkeys during orienting and habituation and after ablation of the amygdala, hippocampus and inferotemporal cortex. Neuropsychologica 3, 111-119. Barham, R.M. and F.J. Boersma, 1975. Orienting responses in a selection of cognitive tasks. Rotterdam: Rotterdam University Press. Bernstein, A.S. and K.W. Taylor, 1979. ‘The interaction of stimulus information with potential stimulus significance in eliciting the skin conductance orienting response’. In: H.D. Kimmel, E.H. van Olst and J.H. Orlebeke (eds.), The orienting reflex in humans. Hillsdale, NJ: Erlbaum. pp. 499-519. Blackman, R., 1966. The effect of the orienting reaction on disjunctive reaction time. Psychonomic Science 4, 411-412. Bloom, L.J. and G.M. Trautt, 1977. Finger pulse volume as a measure of anxiety: further evaluation. Psychophysiology 14, 541-545. Edwards, D.C. and J.E. Alsip, 1969. Stimulus detection during periods of high and low heart rate. Psychophysiology 5, 431-434. Germana, J., 1968. Response characteristics and the orienting reflex. Journal of Experimental Psychology 78,610-616. Germana, J., 1969. Central efferent processes and autonomic-behavorial integration. Psychophysiology 6, 78-90. Graham, F.K., 1979. ‘Distinguishing among orienting, defense and startle reflex’. In: H.D. Kimmel, E.H. van Olst and J.H. Orlebeke (eds.), The orienting reflex in humans. Hillsdale, NJ: Erlbaum. pp. 137-167. Graham, F.K. and J.C. Jackson, 1970. ‘Arousal systems and infant heart rate responses’. In: L.P. Lipsett and H.W. Reese (eds.), Advances in child development and behavior, Vol. 5. New York: Academic Press. pp. 59-117. Hare, R.D., 1972. Cardiovascular components of orienting and defensive responses. Psychophysiology 9, 606-614. Israel, J.B., G.L. Chesney, C.D. Wickens and E. Donchin, 1980. P300 and tracking difficulty: evidence for multiple resources in dual-task performance. Psychophysiology 17, 259-273. Jeffrey, W.E., 1968. The orienting reflex and attention in cognitive development. Psychological Review 75, 323-334. Jennings, J.R. and W. Hall, 1980. Recall, recognition and rate: memory and the heart. Psychophysiology 17, 37-46. John, I.D., 1964. The role of extraneous stimuli in responsiveness to signals: refractoriness or facilitation? Australian Journal of Psychology 16, 87-96. Kahneman, D., 1973. Attention and effort. Englewood Cliffs, NJ: Prentice Hall. Kelly, D.H.W., 1966. Measurement of anxiety by forearm blood flow. British Journal of Psychiatry 112, 789-798. Koepke, J.E. and K.H. Pribram, 1966. Habituation of GSR as a function of stimulus duration and spontaneous activity. Journal of Comparative and Physiological Psychology 61, 422-448. Lykken, D.T., R. Rose, B. Luthur and M. Maley, 1966. Correcting psychophysiological measures for individual differences in range. Psychological Bulletin 66, 481-484. Lynn, R., 1966. Attention, arousal and the orientation reaction. Oxford: Pergamon. Nickerson, R.S., 1973. Intersensory facilitation of reaction time: energy summation or preparatory enhancement. Psychological Review 80, 489-509.

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