Event-related potential studies of language and emotion: words, phrases, and task effects

Anders, Ende, Jungho¨fer, Kissler & Wildgruber (Eds.) Progress in Brain Research, Vol. 156 ISSN 0079-6123 Copyright r 2006 Elsevier B.V. All rights reserved

CHAPTER 9

Event-related potential studies of language and emotion: words, phrases, and task effects Ira Fischler and Margaret Bradley Psychology Department, PO Box 112250, University of Florida, Gainesville, FL 32611, USA

Abstract: This chapter reviews research that focuses on the effects of emotionality of single words, and of simple phrases, on event-related brain potentials when these are presented visually in various tasks. In these studies, presentation of emotionally evocative language material has consistently elicited a late (c. 300–600 ms post-onset) positive-going, largely frontal–central shift in the event-related potentials (ERPs), relative to neutral materials. Overall, affectively pleasant and unpleasant words or phrases are quite similar in their neuroelectric profiles and rarely differ substantively. This emotionality effect is enhanced in both amplitude and latency when emotional content is task relevant, but is also reliably observed when the task involves other semantically engaging tasks. On the other hand, it can be attenuated or eliminated when the task does not involve semantic evaluation (e.g., lexical decisions to words or orthographic judgments to the spelling patterns) or when comprehension of phrases requires integration of the connotative meaning of several words (e.g., compare dead puppy and dead tyrant). Taken together, these studies suggest that the emotionality of written language has a rapid and robust impact on ERPs, which can be modulated by specific task demands as well as the linguistic context in which the affective stimulus occurs. Keywords: language; emotion; event-related potentials; motivation; phrase dominance and control, with verbal threats and promises providing a virtual forum for the basic appetitive and defensive systems that motivate all behavior (e.g., Lang et al., 1997), and that the exquisite informational capacity of language developed from a regulatory, motivational base. The primacy of language as a skill unique to humans, and its ubiquity across societies and individuals, suggests that in order to understand emotional behavior and cognition the story told by language will be an important one. In the studies reported here, effects of emotionality of single word and word phrases are explored as they affect brain processes as reflected in eventrelated potentials (ERPs). Individual words are an appropriate starting point, as words and other morphemes (e.g., the -ed in walked) are the building blocks of meaning in language. But meaning

There are good reasons for those who wish to understand human emotion to be interested in emotion and language. Our waking lives are filled with talk, to others and to ourselves — it has been estimated that the ‘‘stream of conscious experience’’ is largely a stream of self-talk (e.g., Klinger and Cox, 1987). We can be deeply moved, frightened, or aroused by what we hear or read. We actively seek out these kinds of materials, in the news articles, stories, and novels we choose to read. We might argue, in fact, that a primary evolutionary purpose of language is motivational — to influence the thoughts, feelings, and therefore the actions of others in our group. Indeed, some have argued that language developed in part as a tool of social Corresponding author. E-mail: ifisch@ufl.edu DOI: 10.1016/S0079-6123(06)56009-1

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emerges from the sequence of words and phrases, and often is more than the ‘‘sum of its lexical parts’’ — dead is bad, and tyrant is bad, for example, but a dead tyrant is not so bad. In this paper, we report data from a number of different studies that varied the emotionality of individual words, and of simple, two-word phrases.

The motivational organization of emotion When studying emotion in an experimental context, one immediate decision concerns selecting the affective parameters on which stimuli will vary, regardless of whether one uses words, pictures, sounds, movies, or other stimulus materials to induce affect in the laboratory. In the work reviewed here, we define emotion in terms of differences in rated pleasure and arousal of words and simple phrases, relying on a number of theories that propose emotion is organized by dimensions of pleasure and arousal (e.g., Osgood et al., 1957; Lang et al., 1997). Supporting these views, empirical factor analyses of evaluative language consistently have found that the primary dimension underlying people’s judgments of stimuli (that vary from single words to abstract paintings) is hedonic valence, which accounts for the most variance in judgments of meaning (e.g., Osgood et al., 1957; see also Mehrabian and Russell, 1974; Russell, 1980). Hedonic valence is described by scales that, in aggregate, define a continuous dimension that ranges from unpleasant (unhappy, annoyed, despairing, etc.) to pleasant (happy, pleased, hopeful, etc.). Arousal or intensity is the second major dimension that emerges in these factor analyses, and scales defining this dimension extend from an unaroused state (calm, relaxed, sleepy, etc.) to a state of high energy or arousal (excited, stimulated, wideawake, etc.). The relative importance of hedonic valence and arousal has been widely debated. Some have argued that arousal is the primary dimension of emotion. Thus, Lindsley (1951) proposed an influential ‘‘activation theory of emotion’’ (see also earlier formulations by Duffy, 1941 and Arnold, 1945), which was based, in part, on human electroencephalographic (EEG) studies that

showed an association between alpha waves (10–13 Hz) and emotional calm (with even slower waves in sleep) and a progressive increase in frequency with increasing intensity of emotional arousal (from annoyance and anxiety to rage and panic). Other data from research with animal subjects showed that, on the one hand, the brain stem reticular formation (Moruzzi and Magoun, 1949) modulated both EEG frequency and visceral arousal, and on the other, that midbrain lesions blocked emotion, prompting lethargic, apathetic behavior. The importance of emotional arousal in evaluative judgments and affective reactions could be due, in part, to a biphasic organization of emotion arising from its evolutionary and functional heritage. For instance, Lang et al. (1997) proposed that emotion stems from activation of one of two fundamental motive systems in the brain — appetitive and defensive — that have evolved to support behaviors that sustain the life of the individual and the species, accounting for the primacy of the valence dimension in affective expression. These two motivational systems are associated with widespread cortical, autonomic, and behavioral activity that can vary in the intensity of activation. Differences in motivational intensity map onto the arousal parameter in emotion’s dimensional organization. Importantly, arousal is not viewed as a separable system that is independently modulated, but rather as representing the activation (metabolic and neural) initiated by centrally organized appetitive or defensive systems that have evolved to protect and maintain life. In studying how language cues activate the appetitive and defensive motivational systems underlying emotion, it is important to categorize and control verbal stimuli as they vary in hedonic valence and arousal. In a series of individual rating studies, we have collected affective reports of pleasure and arousal for over 1000 English words from many participants. These materials are distributed to researchers in a collection called the Affective Norms for English Words (ANEW; Bradley and Lang, 1998). In each rating study, participants are asked to judge the pleasantness and arousal of each word using the

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Self-Assessment Manikin (SAM) affective rating system devised by Lang et al. (1980). SAM is a graphic (nonverbal) figure that depicts each evaluative dimension using a nine-point scale, and ranges from a smiling, happy figure to a frowning, unhappy figure when representing the hedonic valence dimension (see Fig. 1, ordinate); for arousal, SAM ranges from an excited, wide-eyed figure to a relaxed, sleepy figure (see Fig. 1, abscissa). The SAM measures of pleasure and arousal correlate well with ratings on these evaluative dimensions obtained using a much longer, verbal semantic differential scale (Bradley and Lang, 1994).

In Fig. 1, each word is plotted in a two-dimensional Cartesian space defined by its mean pleasure and arousal rating. There are several characteristic features of the resulting affective space. First, these materials elicit ratings that completely span the hedonic valence dimension ranging from extremely pleasant to extremely unpleasant. Similarly, a wide range of arousal levels are elicited by these materials. Secondly, it is clear that pleasant words range continuously along the arousal dimension: the upper half of emotional space has exemplars at many positions along this dimension. Words labeling unpleasant objects and events, however, tend

Pleasure

Affective Norms for English Words (ANEW)

Men Women

Arousal Fig. 1. Distribution of words in the two-dimensional affective space defined by each word’s mean pleasure and arousal rating (ANEW; Bradley and Lang, 1998), using the Self-Assessment Manikin (SAM; Lang et al., 80).

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to cluster in the high arousal quadrant of emotional space, suggesting that events and objects that threaten life are rarely perceived as calm or unarousing. The distribution of words in affective space is remarkably similar to that of pictures, and of sounds (Bradley and Lang, 2000), suggesting that this distribution represents a relatively fundamental organization of the affective world.

The potency of single words While a single word may not seem like a very potent emotional stimulus, we know that even brief presentations of individual emotionally evocative words can bias attention. The so-called emotional Stroop effect, in which emotionally evocative words, especially threatening words presented to highly anxious, ‘‘hyperattentive’’ individuals, produces greater interference with naming of the color of the word relative to neutral words, suggests an early, possibly preattentive emotional response to these words (see, e.g., Dalgleish, 1995; Williams et al., 1996). Similarly, emotional words presented during a rapid series of briefly presented words (the ‘‘RSVP’’ procedure) can ‘‘capture’’ attention, improving detection of emotional words and targets, and impairing detection of other target words that follow them, the ‘‘emotional blink’’ effect (see, e.g., Keil and Ihssen, 2004; Anderson, 2005; Kaschub and Fischler, 2006). Chapman and colleagues (e.g., Chapman et al., 1980) explored the pattern of ERPs evoked by single emotional words presented in isolation. Their resulting principle component analyses revealed consistent ERP factors associated with each of Osgood’s three dimensions of ‘‘connotative meaning’’ — evaluation, activity, and potency — corresponding roughly to the dimensions of hedonic valence, arousal, and dominance widely used to standardize emotional materials (Bradley and Lang, 1994). A similar set of components was found when the words were being rated on dimensions of the semantic differential, as well as when the words were simply read out loud, suggesting that the emotional response to these words was to some degree independent of the particular way the participants needed to process them.

In Chapman et al. (1980), both emotionally pleasant and unpleasant words elicited an increased positivity in cortical ERPs, compared to emotionally neutral words, as found in a number of studies measuring ERPs when processing words in isolation (e.g., Chapman et al., 1978; Begleiter et al., 1979; Williamson et al., 1991; Skrandies, 1998; Bernat et al., 2001). The emotionality effect in the ERPs to words broadly resembles that obtained when participants look at emotionally evocative pictures (e.g., Cuthbert et al., 2000). In both cases, ERPs to emotionally arousing stimuli diverge from those for neutral stimuli as early as 300 ms after stimulus onset, have a wide topographic distribution, and show little lateral asymmetry (though see Cacioppo et al., 1996). The emotionality effect may disappear within a few hundred milliseconds, and is rarely seen at latencies above 800 ms after word onset.

Early vs. late components to emotional words In view of the effects of word emotionality on tasks like the RSVP detection task noted above, one might expect that ERPs to emotional words might be distinguishable from neutral words quite early in processing, and that these early components might be less task dependent than later differences, which in turn would be more responsive to specific task demands. Bernat et al. (2001) reported an early (P1-N1) divergence of ERPs to mood-descriptor adjectives (e.g., lonely, happy), with unpleasant adjectives more positive than pleasant. The early difference was confined to the left hemisphere sites, and was observed both with supraliminal (40 ms) and subliminal (1 ms, unmasked) presentation of the words. On the other hand, each of the 32 descriptors was shown multiple times during the study, and participants had also generated emotionality ratings for those terms on a number of occasions before the physiological phase of the study. In addition, neutral mood terms were not included, and are important in order to evaluate whether the effects were driven by emotional arousal, or by hedonic valence. More recently, Herbert et al. (in press) presented adjectives that were pleasant, unpleasant, and neutral

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and asked participants to make a covert judgment regarding their emotional response. The earliest significant differences were for ERPs to emotional words (pleasant and unpleasant) becoming more positive than neutral words in the P2 component (180–250 ms post-onset), which continued into P3 (250–400 ms). The difference was predominantly in the left hemisphere, and largest at the central and parietal sites. Pleasantness vs. emotionality Subjectively, the hedonic valence of a stimulus or event appears to be more salient than differences in emotional arousal, especially for printed words. Indeed, as noted above, ratings of hedonic valence for words range much more widely than ratings of arousal (Bradley and Lang, 1998). Although differences in ERPs between pleasant and unpleasant materials have sometimes been reported, there is no consistent pattern that distinguishes between them. More importantly, when neutral words are included in the stimulus set, the ERP pattern typically indicates greater positivity over central–parietal sensors for both pleasant and unpleasant words, relative to neutral words (e.g., Williamson et al., 1991), with little difference between the two classes of emotional words. When differences have been found between pleasant and unpleasant words, it is more commonly the case that unpleasant words elicit a larger and/or earlier divergence from neutral stimuli, than do the pleasant words (e.g., Ito et al., 1998). Taken together, these data suggest that it may be the intensity of motivational activation — whether initiated by activity in appetitive or defensive neural systems — that is critical in modulating the ERP during language processing. Effects of encoding task on ERPs to single emotional words One factor that could clearly impact the effects of emotionality on the ERP across studies is that of the encoding task. Most typically, participants are overtly or covertly evaluating the emotionality or pleasantness of the presented words. In some

cases, there has been no primary task other than to read the words silently, a condition which, given the nature of the materials, may default to a consideration of emotionality. In a series of separate experiments, we contrasted the nature of the encoding task when processing the same set of words. In some of these studies, one or the other dimension of word emotionality was relevant. In others, the emotional attributes of the words were irrelevant to the decision. Normative ratings of emotionality were carefully controlled, and we examined the consequence of task manipulations on the latency and morphology of emotionality effects in the ERPs, which were recorded at five scalp locations (see below). In these studies, a set of 150 words was drawn from the ANEW (Bradley and Lang, 1998). The stimuli included five subsets of words from different regions of affective space: pleasant, high-arousal words (e.g., passion), unpleasant, high-arousal words (e.g., vomit), pleasant, low-arousal words (e.g., bunny), unpleasant, lowarousal words (e.g., ugly) and neutral, low-arousal words (e.g., rattle). For clarity, this chapter focuses on data that compare ERPs for the most arousing emotional stimuli (i.e., high-arousal pleasant and unpleasant words) as they differ from neutral, low-arousal words. In each stimulus set, both nouns and adjectives were included, but there were no words directly describing emotional states of either type (e.g., happy or happiness). Word length, frequency, and imagery ratings were also balanced across the sets. In each of five studies, each of the 150 critical words was presented once, in random order, during the course of the experiment. Each trial began with a fixation box signaling the start of the trial. Around 1/2 s later, one of the words was presented, centered on the point of fixation. Word duration was 175 ms, but the fixation box remained visible until 2 s after word onset. EEG was sampled at a 125 Hz rate, with a bandpass of 0.1–40 Hz during the period from 100 ms prior to word onset to 1000 ms after word onset. EEG was then rereferenced offline to the average of the mastoids, and trials with blinks and other artifacts were rejected prior to averaging. Participants with greater than 15% rejection rate were discarded,

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and sufficient sessions were conducted to obtain data for 30 participants in each experiment.

Decisions about pleasantness We began the series by asking a group of participants to judge word pleasantness at encoding. In a pilot study, this task was presented as a two-choice bipolar decision (pleasant, unpleasant) that was to be made as soon as the word was shown. Perhaps not surprisingly, response time for neutral words was significantly slower than for affective words, as the neutral items were neither pleasant nor unpleasant, making the decision difficult. Thus, in the actual Pleasantness Decision study, we allowed three choices at encoding — pleasant, unpleasant or neutral — and delayed the overt response until the end of each trial. The ERPs for the pleasant, neutral, and unpleasant words from the Pleasantness Decision study are shown in Fig. 2. As illustrated in this figure, ERPs to the pleasant and unpleasant words diverge from that for neutral words around 450 ms after onset, taking the form of an enhanced late positive potential (LPP) peaking around 500 ms. Shortly thereafter, ERPs for pleasant and

unpleasant words become negative through the slow wave (SW) region more rapidly than do the ERPs for neutral stimuli. This overall pattern can be seen at each of the sensors. The contrast between emotional words (pleasant and unpleasant), on the one hand, and neutral words, on the other, was significant both in the LPP and the later SW region, and the size of the difference did not vary across sites. Importantly, there was no difference in ERPs between pleasant and unpleasant words at any time point or sensor site, despite the task relevance of this affective dimension. The lack of ERP differences before nearly 1/2 s after word onset suggests that the earlier onset of emotionality effects in prior studies of single words may be due either to repetition of the target words, or (as we believe) to the particular task given the participants. The lack of any differences in the ERPs for the pleasant and unpleasant words, as salient and as task relevant as the valence distinction was in this study, is striking, and is consistent with the primarily arousal-driven nature of the response to these stimuli as seen in the ERPs. The later SW negativity seen for the emotional words compared to the neutral words may be nothing more than an enhanced contingent negative variation (CNV), reflecting the fact that the decision

Fig. 2. Event-related brain potentials at five scalp locations following presentation of affectively unpleasant, neutral, and pleasant words. In this experiment, participants decided whether each word was pleasant, neutral, or unpleasant.

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and response selection for the pleasant and unpleasant words continues to be easier than for the neutral words.

Decisions about emotionality In the second experiment, participants were required to classify the words as emotional (whether pleasant or unpleasant) or as unemotional, neutral words. Note that if this decision were made by first detecting whether the word was pleasant or unpleasant, and inferring that it should be therefore classified as emotional, the task becomes logically identical to the Pleasantness Decision, with an added step that might slow the overall decision, but should have no impact on the ERPs. Interestingly, however, the ERPs look quite different from those of the first experiment. As illustrated in Fig. 3, the ERPs for emotional words now diverge earlier and are visible as early as 300 ms post-onset, are significant in the N400 region and continuing into the LPP. Also in contrast to the results of the data from the Pleasantness Decision study, there is now no sustained difference between the emotional and the neutral words after about 600 ms.

This shift in the ERP emotionality effect indicates that the intensity of motivation activation — whether appetitively engaging or defensively activating — is the aspect of emotionality that is first apparent in the ERP. Both appetitively and defensively engaging stimuli often signal the need for immediate attention (and often action) and the ERP appears to reflect the behavioral and attentional adjustments to stimuli with motivational relevance. That is, the ERP appears to reflect cortical processes of heightened attention and preparation for action that is common for all motivationally salient stimuli, rather than reflecting hedonic distinctions. Note, however, that even with this slight shift in the ERP, there are still no apparent differences in the early components that are commonly associated with the processes that either precede or direct conscious attention and awareness.

Silent reading If, as we speculated earlier, simply reading a series of words that vary in affect might result in an emotionality effect in the ERPs, and that emotional arousal, rather than the pleasantness, of

Fig. 3. Event-related brain potentials at five scalp locations following presentation of affectively unpleasant, neutral, and pleasant words. In this experiment, participants decided if each word was emotionally arousing (whether pleasant or unpleasant), or unemotional.

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words is the dimension that dominates the ERPs, we might expect that silent reading of these words with no decision at all might closely resemble the data from the Emotionality Decision study. In the third experiment, then, the same set of words was presented to participants who were now asked to read the words and ‘‘think about their meaning.’’ No overt decision or response was required, however. Results of this study are illustrated in Fig. 4. In general, the magnitude of the ERP emotionality effect is somewhat diminished, compared to the previous experiments, but the pattern is clearly more similar to that found for the emotionality decision (Fig. 3) than for the pleasantness decision (Fig. 2). The contrast between the emotional words and neutral words was significant in the LPP region (450–650 ms post-onset), and as for the data from the Emotionality Decision study, there is no difference among the word classes in the SW region of the ERPs. The somewhat smaller effects found in this experiment compared to the previous one are likely due to the lack of task demands that would engage participants in actually reading the words for meaning. In contrast to emotional pictures, for example, it is not surprising that single words may

have less ability to automatically engage comprehension of the meaning of the words. Nonetheless, given that participants could choose to be rather passive in their response to the words, the continued effect of emotionality in the LPP region is an impressive demonstration that even for these wholly symbolic stimuli, the derivation of meaning is, to some degree, hard to avoid, as these single words continued to elicit a measurable emotional response.

Semantic categorization In each of the preceding experiments, word emotionality was either an explicit or implicit focus of the task. In each case, a robust, arousal-driven LPP effect was seen beginning as early as 300 ms after word onset, and showing little difference between pleasant and unpleasant words. We wondered whether these effects would continue to be seen if the decision involved an attribute of the words that was orthogonal to their emotionality. In the fourth study in this series, we included a set of 60 target words, 30 from each of two taxonomic categories — tools and articles of clothing.

Fig. 4. Event-related brain potentials at five scalp locations following presentation of affectively unpleasant, neutral, and pleasant words. In this experiment, participants read each word silently and made no decision or overt response.

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Participants were asked to press a response button whenever they saw a word from one of these two target categories, and make no response to the remaining (critical) words. The semantic decision is a relatively deep one, requiring that the meaning of each word be derived and a specific semantic attribute evaluated. The use of two categories was intended to discourage a strategy wherein participants could maintain a list of common category exemplars in working memory, and match these to presented words. Results from this task are shown in Fig. 5. Despite the irrelevance of emotion to the task, there were again differences due to word emotionality in the ERPs in the LPP region that is maximal at the Cz location, somewhat larger on the left posterior (P3) site, and absent on the right anterior (F4) site. In contrast to when emotion was task relevant, however, there is no sign of any divergence until well into the rising portion of the LPP, and the effect was not significant until 500 ms after word presentation. Moreover, the difference comes and goes within a span of 200 ms. Again, there is no sign of any emotionality differences in the SW region. Also in contrast to the previous studies, the ERP is only significantly different from neutral words

for the unpleasant, but not the pleasant, stimuli. This is quite interesting, particularly in view of the equivalence of the ERPs for pleasant and unpleasant words in the other experiments. It suggests that the effect of hedonic valence in the present task is not merely due to differences in emotional arousal — otherwise, it should have been present or enhanced when arousal was task relevant — but is in fact due to the greater ability of the unpleasant words to attract attention under conditions when emotionality is irrelevant to the task.

Lexical decision In the semantic decision task, a rather deep semantic analysis of the words was needed, in order to categorize them. The continued presence of an emotionality effect in the ERPs for the unpleasant words led us to wonder if a more superficial task that still required lexical access would further diminish or eliminate the emotionality effect. On the one hand, deciding whether or not a string of letters is a word does not require accessing the meaning of the word. On the other hand, a long tradition of research on semantic priming effects in

Fig. 5. Event-related brain potentials at five scalp locations following presentation of affectively unpleasant, neutral, and pleasant words. In this experiment, participants pressed a key if a word was a member of one of two semantic categories (tools or articles of clothing, represented by a set of filler words), and made no response to the critical words, none of which was from those categories.

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the lexical decision task (e.g., Meyer and Schvaneveldt, 1971; Fischler, 1977; Holcomb, 1988) suggests that the core meaning of a word may be automatically activated during this task. A final experiment in the series was therefore conducted in which participants were shown the same set of 150 critical words, along with 60 nonwords that had been created by changing the target words from the two taxonomic categories (tools and clothing) by a single letter. Participants were to press a response button whenever a nonword was shown, and to make no overt response to any of the words. The ERPs obtained during this lexical decision task are presented in Fig. 6. The robust emotionality effect for the unpleasant words that was obtained in the Semantic Decision study has been largely eliminated, even over the central sites. Although there is a slight trend toward an emotionality effect at the vertex, the ERP difference among the classes of words did not reach significance at any site or in any temporal window. These results suggest that when words are read but there is no need to consider their meaning, and emotionality is irrelevant to the decision, affective attributes of words have little effect on the reader. Overall, our studies of ERPs to single words show that under a variety of tasks, emotionally

evocative words elicit a fairly rapid brain response as seen in the ERPs. For the most part, pleasant and unpleasant words affect the ERPs similarly, and there is little evidence for differences in hedonic valence of word stimuli across these studies. The one exception, in the semantic decision task, suggests that unpleasant or threatening words are more likely to elicit a response under conditions when participants are not oriented toward dimensions of emotionality. Clearly, too, there are some limits to the automaticity of even this emotional attention capture by single words, as seen by the lack of emotionality differences in the ERP when people need only to make lexical decisions. The absence of ERP differences as a function of word emotionality earlier than about 300 ms in any of these experiments, even when the encoding task directly focuses on the emotional meaning of words, is striking, and contrasts with at least some demonstrations of such effects with single words discussed earlier (e.g., Bernat et al., 2001). Given that estimates of the time needed for ‘‘lexical access’’ — the activation of the representation of a word as a linguistic object in memory — is of the order of 200 ms, and that presumably the associations that link that word to emotional experiences or ideas must also take time to be activated, it

Fig. 6. Event-related brain potentials at five scalp locations following presentation of affectively unpleasant, neutral, and pleasant words. In this experiment, participants pressed a key if the item was a nonword, and made no response to the words.

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perhaps would be more surprising than not to find emotionality effects in cortical ERPs for words prior to 200 ms.

When words combine: comprehension of simple emotion phrases Words are the fundamental semantic units of language. But the combination of words into phrases and sentences provides language with its expressive power, as these combinations often convey meanings that could not be predicted from the meaning of the individual words (e.g., Murphy, 1990). The noun phrase, in a sense, is thus the fundamental unit of discourse and communication through language. The second series of experiments to be reviewed here concerns how the affective response to emotionally potent simple two-word phrases compares to that obtained when words within a phrase are treated as isolated units. Given the stable pattern of ERPs to emotional words in isolation, what might we expect when words are combined into meaningful phrases? It may be that the effects of emotionality on the ERP to words within sentences are no more than the sum of the ERP to each word presented in isolation. If this is the case, we should see an emotionality effect to the first word of the pair with the same time course as that for emotional words in isolation. Hence, a pair such as starving murderer should show an increased positivity beginning around 250–300 ms to starving than to a neutral word such as resting. Note that, as a consequence, the ERP to murderer may also differ in these cases because of carry-over effects from the first to the second word. An alternative hypothesis, more consistent with the view that words in linguistically coherent sequences may be processed differently from those in isolation (see Bellezza, 1984), is that the emotional response of the first word may be deferred until it is known what it is modifying. Compare, for example, a dead tyrant, or a dead puppy. A dead tyrant may well be a good thing; a dead puppy is usually not. On the other hand, a dead letter is fairly neutral. According to this view, effects of emotionality may not develop until the second

word is processed, and may reflect the affective meaning of the word pair rather than that of the second word alone. Hence, pairs such as starving murderer and resting murderer should show no emotionality effect at all for starving and resting, but a larger emotionality effect, as measured on the second word, for the pair starving murderer than for the pair resting murderer. The second question regarding word emotionality addressed in this research concerns the relationship between the hedonic valence of the first and second words. Superimposed on any arousal effects of the modifier and/or noun, the affective congruence of the words of a pair may affect ERPs. Pairs with mismatched affect between modifier and noun (e.g., laughing murderer) may elicit a distinctive ERP pattern compared to pairs that match in hedonic valence (e.g., dead murderer), especially when the task involves comprehension of the pair as a coherent phrase. Note that this effect could be independent of any arousal-based effects of the first and second word separately, since emotional arousal is the same for the matched and mismatched pairs. On the one hand, there is some evidence for emotional congruence effects in word processing tasks, including the so-called affective priming effect, in which decisions about emotional target words are speeded by prior presentation of affectively congruent prime words (e.g., death– aggressive) and slowed by incongruent prime words (e.g., death– happy) (e.g., Fazio et al., 1986; Klauer, 1998; Wentura, 2000). This priming effect appears to require a rather short (c. 200–300 ms) interval between prime and target onset (stimulus onset asynchrony, or SOA; see Bargh et al., 1992). On the other hand, as we reviewed above, there is little evidence that affective valence modulates the ERPs to individual emotional words upon which a valence-driven congruence effect might be based (although see Ito et al., 1998). Moreover, in the present studies, a relatively long SOA between first and second words of a pair (750 ms) was used, as we wanted to allow enough time for the first word to elicit the emotionality response, and to detect this emotionality component if it is present. We also wanted to maximize the potential impact of the emotionality of the first word on the second

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by presenting the second word at a point when the effects of arousal, based on our studies with word in isolation, might be at a peak (500–700 ms postonset). For these reasons, we anticipated that the effects of matching or mismatching the hedonic valence of the modifier and noun of our pairs might have little impact on the ERPs to the second word in these experiments. In each of the experiments presented here, participants were shown a series of word pairs that formed modifier–noun phrases. In the first experiment, the task was to judge if the pair formed a ‘‘linguistically coherent phrase.’’ In the second study, in contrast, the same pairs were presented, but the task was to judge if either word came from a target semantic category. Our hypothesis was that the phrase task would produce diminished emotionality effects to the first word, and enhanced effects to the second, compared to the word task.

Comprehension of noun phrases Nine sets of 20-word pairs each were created, with emotionality of the first and of the second words (pleasant, neutral, and unpleasant) controlled and varied factorially. Three sets of twenty nouns each were selected from the ANEW (Bradley and Lang, 1998) to be used as second words in these noun phrase pairs. The sets varied in rated pleasantness, with both pleasant (e.g., lover) and unpleasant (e.g., suicide) words rated similarly higher in arousal than were neutral words (e.g., banner, see Table 1). The sets were comparable in length, Table 1. Mean ratings of valence (pleasantness) and arousal (from the Bradley & Lang, 1998, norms) for the words used in the Word Pair experiments (see text)

Pleasant 7.9 Neutral 4.8 Unpleasant 2.1

First Words

Second Words

Valence Arousal

Valence Arousal

6.0 4.4 5.5

8.2 4.9 1.8

6.3 4.7 6.3

Note: A 1–9 scale is used for the SAM ratings, with 9 the most pleasant/arousing.

frequency, and rated imagery value. Three additional sets of twenty words were also selected from the ANEW, again comparable in length, frequency, and imagery, to be used as first words in the pairs (see Table 1). Each of these words was paired with a pleasant, neutral, and unpleasant second word such that each combination made a relatively coherent (though sometimes semantically odd) adjective–noun phrase (e.g., terrible suicide, slow suicide, happy suicide). In addition, a set of 20 word pairs was constructed such that the first and second words did not form a ‘‘coherent’’ phrase, for example, foot sentence. Participants were told that the study concerned brain activity associated with understanding simple phrases and making decisions regarding the coherence of simple phrases. No mention was made of the emotionality of the words. Examples of linguistically ‘‘coherent’’ and ‘‘incoherent’’ word pairs were given, and it was explained that an overt response should be made only to pairs judged as incoherent, which would occur fairly infrequently. On each trial, a fixation mark was followed by the first word, centered at the point of fixation. The word remained visible for 250 ms. The second word was presented in the same location 750 ms after first word onset, and also remained visible for 250 ms. Grand averaged ERPs were obtained across 20 participants for each of the nine experimental word pair conditions. The ERPs to the first words as a function of emotional class (and averaged across second word class), are shown for five cortical sites in Fig. 7. Most notably, as predicted, there was no difference between the pleasant, neutral, and unpleasant words at any point prior to onset of the second word. The ERPs to the second words of the phrase, averaged across first word emotionality, are shown in Fig. 8. As illustrated in the figure, emotional second words — both pleasant and unpleasant — elicit a more positive-going ERP than do neutral words, diverging around 350 ms post-onset at centroparietal sites and continuing through the end of the recording epoch. The ERP emotionality effect for the word completing the phrase appears broadly similar to that observed when single words are presented and participants are judging their emotionality (see Fig. 4). Effects of emotionality

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Fig. 7. Event-related brain potentials at five scalp locations following presentation of an affectively unpleasant, neutral, and pleasant first word of a two-word phrase. In this experiment, participants pressed a key when they judged the complete pair to be ‘‘linguistically incoherent’’ (represented by a set of filler pairs; see text).

Fig. 8. Event-related brain potentials at five scalp locations following presentation of an affectively unpleasant, neutral, and pleasant second word of a two-word phrase. In this experiment, participants pressed a key when they judged the complete pair to be ‘‘linguistically incoherent’’ (represented by a set of filler pairs; see text).

were significant in a 350–450 ms time window, in the LPP time window (450–600 ms), and in the SW window (600–750 ms). In each case, the ERPs to the unpleasant and pleasant nouns were significantly more positive than they were to the neutral

words, although the comparison between pleasant and neutral nouns was only marginal (po0.06) in the earliest time window. The difference between pleasant and unpleasant words never approached significance. Moreover, the effects were present at

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each recording site, with no significant topographic differences in the ANOVAs on the scaled amplitudes. An effect of emotional congruence on the ERPs in these analyses would have appeared as a significant interaction of first and second word valence in the ERPs to the second word, with matched-valence ERPs (pleasant/pleasant and unpleasant/unpleasant) diverging from mismatched ERPs (pleasant/unpleasant and unpleasant/pleasant). This interaction never reached significance, for any site or interval. Also, there were no main effects of first word valence on the ERPs to the second word. Taken together, the pattern of ERPs to the emotional word pairs in this experiment was straightforward. First, emotionality of the first (modifier) words had no impact on the ERPs to these words, despite the use of words whose emotionality ratings were at least as strong, in hedonic valence and emotional arousal, as in earlier studies of words in isolation, and despite the use of a task requiring semantic analysis of both words, and an interval between first and second words in which emotionality effects had been clearly seen in prior work. Second, there were clear effects of emotionality of second words — the modified nouns — on ERPs. Third, as with earlier studies, these ERP effects were driven by the emotional intensity (arousal) of the words rather than by differences in hedonic valence; in no case did the pleasant and unpleasant second words systematically differ from each other in the ERP.

Comprehension of single word within noun phrases The lack of emotionality effects for the first words in this experiment is presumably a consequence of the coherence encoding task, which required comprehension of the word pair as a phrase. The affective meaning of the first word thus must await the completion of the entire phrase. To test this hypothesis, the same word pairs were presented with the same timing, using an encoding task that directed attention to the meaning of each individual word of the pair, rather than the phrase as a unit. In the last experiment to be reviewed, this was done by

presenting occasional target words from one of two prespecified semantic categories, and requesting participants to monitor each word pair for the occurrence of one of these target words. There is substantial evidence that, for sentences at least, comprehension of meaning at the phrase level may not be automatic. For example, Fischler et al. (1985; see also Fischler and Raney, 1991) found that the truth value of sentences such as A robin is a bird/A robin has a bird modulated the size of the N400 priming effect when the task was sentence verification, but not when the task was to judge the semantic relatedness of the first and second nouns (see also Brega and Healy, 1999). Our hypothesis, then, was that the focus on individual words rather than phrases in the second experiment in this series would elicit emotionality effects in the ERPs to the first words. In contrast, if the adjectives used were simply not potent enough to elicit an emotional response, then changing the task should have little effect on the ERP results, with first words again showing no emotionality effect. Regarding the pattern of congruence effects, there were several possibilities. Klauer and Stern (1992) have suggested that affective congruence effects depend on the ease with which the prime and target words can be implicitly thought of as a pair. This would imply that congruence effects should have been observed in the phrase task, however. If we are successful in eliciting an emotionality response to the first word by requiring a decision to it, this might set the stage for such match/mismatch effects between the first and second words. Nonetheless, the SOA remains substantially longer than those typically found to produce affective priming effects (see Bargh et al., 1992; Wentura, 2000), and thus congruence effects were not strongly expected in this experiment. The design and materials of this experiment were identical to that of the phrase coherence task, with the exception that the twenty incoherent pairs were modified so that one of the two words came from one of two semantic categories: tools and articles of clothing. Participants were told to read each word of each pair, and press a response button when a word from one of the two target categories was shown. Several examples of category instances were

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Fig. 9. Event-related brain potentials at five scalp locations following presentation of an affectively unpleasant, neutral, and pleasant first word of a two-word phrase. In this experiment, participants pressed a key when they judged either of the two words of the pair to be a member of one of two semantic categories (tools or articles of clothing, represented by a set of filler pairs; see text).

given. As before, the SOA was 750 ms, and each participant saw all 200 pairs, in random order. The ERPs to the first words, as a function of hedonic valence (and averaged across second word valence), are shown for the five cortical sites in Fig. 9. The major morphological features of the ERPs at the frontal and central sites, as well as the more complex waveform parietally, correspond closely to those observed in the noun phrase task. The most notable overall difference from the pair coherence experiment is that now there is a substantial emotionality effect in the ERPs. Emotional words (either pleasant or unpleasant) again prompt more positive potentials, compared to neutral words, which is apparent around 400 ms and continues into the LPP region at centrofrontal sites. The effects, which were significant in the 350–450 ms interval and were marginal just before and after this time window, were entirely due to a difference between emotional and neutral conditions, with ERPs to pleasant and unpleasant words essentially identical to each other and both different from that elicited for neutral words. The ERPs to the second words as a function of hedonic valence (and averaged across first word

valence) are shown for each recording site in Fig. 10. The only time window resulting in a significant effect of word emotionality is 450–600 ms after onset of the second word. As before, contrasts showed that the difference is due to greater positivity for ERPs to pleasant and unpleasant words, compared to neutral words, with no difference in the ERPs between the emotional words. The effect did not differ across electrode site. There was little evidence of an interaction between first and second word valence at any site except for a slight trend in the 600–750 ms time window at P3. The pattern of amplitudes across conditions at this interval was complex, however, and did not easily lend itself to an affective priming interpretation. In sum, the data clearly show that when the words of a pair that potentially form a coherent phrase must be comprehended as individual words, the emotionality of the first as well as the second word results in an enhanced positive-going ERP. This contrasts with the ERPs to the identical words when the two items are treated as a noun phrase. On the other hand, there was no evidence that emotional congruence of the items affected ERPs to the second word in the pairs.

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Fig. 10. Event-related brain potentials at five scalp locations following presentation of an affectively unpleasant, neutral, and pleasant second word of a two-word phrase. In this experiment, participants pressed a key when they judged either of the two words of the pair to be a member of one of two semantic categories (tools or articles of clothing, represented by a set of filler pairs; see text).

Emotionality effects on the ERPs to the first and second words of a word pair, then, was critically affected by the task. When the word pairs were considered as phrases, effects of emotionality of the first word (i.e., the modifier) were wholly absent, but when the pairs were treated as two separate words, a significant emotionality effect was observed in the ERP elicited by the first word. This demonstrates that the absence of these effects in the noun phrase task is not due to the particular words used, or to the word class of adjectives vs. nouns. Rather, we conclude that when word sequences can form phrases, and are treated as such, the emotional response to the modifying adjectives is deferred until, so to speak, one knows what is being modified: is it a tyrant, a puppy or a letter that’s dead? That is, the hedonic valence is only apparent at the level of the word phrase, rather than at the level of the individual words. The shift from phrase- to word-level tasks had the opposite effect on the emotional response to the second words, reducing the ERP differences in size, as well as in temporal and topographic extent. This reduction is consistent with the view that for phrases, the emotionality effect in the ERPs is wholly driven by the emotionality of the phrase,

rather than determined by a sequential cascade of emotionality effects to each word in turn. The emotionality effect for second words in the noun-phrase task was greatest, in fact, not to the most emotionally arousing individual words, but to the most emotionally arousing phrases, as shown by a post hoc analysis of emotionality ratings of the phrases. The contrasting effects of emotionality in the two experiments suggest limits to the automaticity of comprehension of emotional aspects of word meaning, in at least two ways. First, consistent with the findings of our studies of single words, even when the meaning of words is being processed, as in both experiments here, the response to their emotionality depends on the current task, with some tasks failing to elicit any emotionality effects in the ERPs. Second, consistent with the findings of Fischler et al. (1985) and others, the meaning of phrases and clauses requires attention at that level of analysis. When words in a sequence are treated as isolated lexical events, on the other hand, even if they have the potential to be integrated into phrases, the impact of phrase-level meaning is attenuated. In contrast to the effects of word emotionality and task on the ERPs, there was little effect of the

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congruence or incongruence of emotional valence on the ERPs in either experiment. Since we did observe what might be considered a congruence effect in the behavioral data — the coherence ratings were higher, and the probability of ‘‘incoherent’’ responses was lower for emotionally congruent than incongruent pairs — it may be that the ERP measure is simply insensitive to the hedonic valence dimension of emotionality of words. However, this seems unlikely given the several positive findings of congruence effects in very different paradigms (e.g., Cacioppo et al., 1993; Chung et al., 1996). Alternatively, such effects with the present materials and tasks may be observable only when the SOA between first and second words is much shorter, as is the case for the affective priming studies (see above) — under 300 ms. To summarize the main results, the pattern of emotionality effects for ERPs suggests that when words are combined into phrases, and treated as phrases, the emotional response to these pairs is driven by the emergent meaning of the pair as a linguistic unit, rather than a sequential unfolding of emotionality effects to individual words that cascades into an overall emotionality effect. This is seen in the absence of emotionality effects to the first words and the enhanced emotionality effects to the second word (compared to our prior work, at least). In this view, the absence of systematic congruence effects between first and second words also makes sense: if there is no emotionality response to the first word as such, then there is nothing to be congruent or incongruent with the second word. What matters is the meaning of the phrase.

Comprehending words, phrases, and sentences Across these studies, there is consistency in how emotionality affects the brain’s response to words. ERP differences generally took the form of a broad increase in the magnitude of a late positive potential for pleasant and unpleasant words, relative to neutral words. This emotionality effect occurs around a half second after word onset, although it can emerge as early as 300 ms post-onset, and can endure for several hundred milliseconds or longer. The effect is maximal at central and

parietal sites, with only a slight trend toward a leftmaximal lateral asymmetry. With few exceptions, there is little difference between pleasant and unpleasant words in these ERPs. This pattern of ERP modulation is strikingly similar to that found when people view emotional pictures: in both cases, a late positive potential, emerging around 300–400 ms after stimulus onset and maximal over central–parietal sensors is apparent, which is heightened for emotionally engaging, compared to neutral, stimuli (e.g., Cuthbert et al., 2000). For both pictures and words, ERPs primarily reflect the intensity or arousal parameter of emotion, rather than differences in hedonic valence. One interpretation is that the late positive component of the ERP reflects heightened attention allocation to motivationally salient stimuli, which is implemented in cortical structures and initiated by activity in subcortical structures differentially engaged by appetitive and defensive stimuli. Because the ERP only weakly reflects differential subcortical activity, however, it instead reflects the heightened attention and engagement that is found when emotional (whether pleasant or unpleasant) cues are encoded. Collectively, the studies reviewed here also show how the specific encoding task, and also whether the words are presented in isolation or embedded in other words as part of phrases impact the presence, timing and extent of ERP emotionality effects. It is a reminder that, as claimed by Gestalt psychologists and ‘‘interactionist’’ psycholinguists, a sentence is more than the sum of its lexical parts. To understand how emotion is comprehended through language, it is necessary to consider both the local and global aspects of language processing, as well as the larger context in which we hear or read of emotional events.

Acknowledgments The research described here was supported by NIMH grants to each author as investigators in the NIMH Center for the Study of Emotion and Attention (P50-MH52384) at the University of Florida. The first series of experiments, on effects of single emotional words, was done in

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