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Memory & Cognition 2002, 30 (4), 583-593

Spoken word recognition relies on an acoustic speech sig- nal that carries information not only about the linguisticcon- tent of a talker’s utterance, but also about speaker-specific characteristics, such as talker identity, social status, and psychological state. In particular, a speaker’s intonation, prosody, vocal effort, and speaking rate can convey an enor- mous amount of information about his or her emotional state (see, e.g., Murray & Arnott, 1993; Sherer, Banse, Wall- bott, & Goldbeck, 1991). Although both linguisticand non- linguistic properties of spoken language are crucial for suc- cessful linguistic interpretation, relatively little attention has been paid to the integration of these two types of in- formation in research on spoken language processing. In the present study, the nature of this integration is investi- gated by examining the influence of emotional tone of voice on the resolution of lexical ambiguity.

It is well known that spoken language is filled with am- biguities at the lexical level. Words often have more than one meaning, and listeners must resolve this ambiguity to access the appropriate meaning of a given lexical item. Re- search in which this issue has been investigated has fo- cused primarily on determining at what point during the course of spoken language processing semantic and sen- tential context serve to disambiguate lexical items (e.g., Moss & Marslen-Wilson, 1993; Paul, Kellas, Martin, & Clark, 1992; Simpson, 1994). The question of what kind

of context can serve to disambiguate or bias the selection of a particular word meaning has received relatively less attention. Although investigators have examined which as- pects of sentential context serve to influence lexical se- lection (Kellas, Paul, Martin, & Simpson, 1991; Paul et al., 1992; Tabossi, 1988), contextual factors other than sen- tential context have not necessarily been examined sys- tematically. It has been assumed, either implicitly or explic- itly, that nonlinguistic aspects of spoken language are not necessarily relevant to lexical access and selection. On the one hand, researchers have investigated how the linguistic content of speech—the syllables, words, and sentences of speech—are processed and represented (e.g., Luce, Pisoni, & Goldinger, 1990; Marslen-Wilson & Warren, 1994; McClelland & Elman, 1986). On the other hand, re- searchers have investigated how listeners perceive the emotional state of a speaker from affective tone of voice (e.g., Frick, 1985; Murray & Arnott, 1993; Pittam & Scherer, 1993). Thus, these two areas of research have largely been considered separately (but see Friend, 1996; Wurm & Vakoch, 1996).

This assumption of independence stems in part from traditional explanations of linguistic processing and rep- resentation. Properties of the speech signal, such as emo- tional tone of voice, have been viewed as a source of noise that the perceiver must strip away or normalize to retrieve the abstract, canonical linguistic representations thought to underlie subsequent stages of linguistic processing (Halle, 1985; Joos, 1948; Kuhl, 1991, 1992; Shankweiler, Strange, & Verbrugge, 1977). According to this view, non- linguistic characteristics, such as tone of voice, should have little influence on linguistic processing. Contextual cues, such as emotional tone of voice, should not constrain lexical activation and selection.

Recently, however, research has suggested that variabil- ity in spoken language may not be stripped away during the early stages of speech perception but, rather, retained

583 Copyright 2002 Psychonomic Society, Inc.

Portions of this research were presented at the 134th Meeting of the Acoustical Society of America, San Diego, December 1997. The authors thank Audrey Katz, Anna Katz, Michael Koslowski, and Adam Warden for their assistance with data collection. In addition, we thank Arthur Samuel and Stephen Goldinger for helpful suggestions concerning re- vision. Correspondence concerning this article should be addressed to L. C. Nygaard, Department of Psychology, Emory University, Atlanta, GA 30322 (e-mail: [email protected]).

—Accepted by previous editorial team

Resolution of lexical ambiguity by emotional tone of voice

LYNNE C. NYGAARD and ERIN R. LUNDERS Emory University, Atlanta, Georgia

In the present study, the effects of emotional tone of voice on the perception of word meaning were in- vestigated. In two experiments, listeners were presented with emotional homophones that had one af- fective meaning (happy or sad) and one neutral meaning. In both experiments, the listeners were asked to transcribe the emotional homophones presented in three different affective tones—happy, neutral, and sad. In the first experiment, trials were blocked by tone of voice, and in the second experiment, tone of voice varied from trial to trial. The results showed that the listeners provided more affective than neutral transcriptions when the tone of voice was congruent with the emotional meaning of the ho- mophone. These findings suggest that emotional tone of voice affects the processing of lexically am- biguous words by biasing the selection of word meaning.

584 NYGAARD AND LUNDERS

and used (e.g., Pisoni, 1993). Several studies using both explicit and implicit memory tasks have demonstrated that variation in the speech signal due to talker’s voice is re- tained in memory along with linguistic content (Bradlow, Nygaard, & Pisoni, 1999; Church & Schacter, 1994; Gold- inger, 1996, 1998; Nygaard, Sommers, & Pisoni, 1995; Palmeri, Goldinger, & Pisoni, 1993; Schacter & Church, 1992). Schacter and Church, for example, have shown that listeners are sensitive to changes in talker’s voice from study to test in implicit memory tasks, such as auditory stem completion. Listeners were more likely to complete an auditory stem with a word from the previously presented list if the stem was repeated in the same voice, as opposed to a different voice. Similarly, Palmeri et al. found that talker characteristics are retained in episodic memory as well. In a continuous recognition memory task, listeners were more likely to recognize a previously presented word if it was repeated in the same voice, as opposed to a different voice.

In addition to talker identity, other types of variation in the speech signal have been shown to influence word recog- nition as well. Studies have shown that intonation (Church & Schacter, 1994), speaking rate (Bradlow et al., 1999), and vocal effort (Nygaard, Burt, & Queen, 2000) all ap- pear to be retained in lexical representations. Nygaard, Burt, and Queen found that recognition memory performance was superior when words were repeated with the same vocal effort than when repeated with a different vocal ef- fort (e.g., shouted vs. whispered speech). Although these repetition effects were mediated by the judged typicality of a particular surface form type, it does appear that listen- ers are extremely sensitive to the perceptual characteris- tics of language.

The research on the retention of talker-specific charac- teristics in speech calls into question two basic assumptions of traditional abstractionist explanations of spoken lan- guage processing. The first is that the end product of per- ception is a series of abstract, canonical linguistic repre- sentations. Rather, this research suggests that lexical representations may be perceptually grounded. Goldinger (1998; see also Jusczyk, 1993) has proposed that lexical representations are exemplar based. Each instance of a previously heard word may be retained in memory and may contribute to subsequent word recognition. The sec- ond assumption is that nonlinguistic properties of speech are irrelevant with respect to the initial stages of language processing. Given the importance that nonlinguisticproper- ties have in spoken communication and given that these properties are retained in long-term memory, these prop- erties may influence linguistic processing. Nygaard, Som- mers, and Pisoni (1994; Nygaard & Pisoni, 1998) found that listeners who learned the talker-specific characteris- tics of speech were better able to extract linguistic content. These results suggest not only that listeners learned specific nonlinguistic characteristics of speech, but also that this learning helped them recover the linguistic content.

Although the perceptual details of spoken words appear to be preserved and used during spoken language pro-

cessing, the question remains as to how and whether the information that these nonlinguisticattributes of speech pro- vide is integrated into ongoing language processing and representation. Certainly, tone of voice provides the listener with an enormous amount of information about the emo- tional state and communicative intent of conversational partners. Listeners can identify particular emotions from a talker’s voice (see, e.g., Frick, 1985; Pittam & Scherer, 1993), and difficulties with decoding nonverbal aspects of speech can result in social and interpersonal problems (see, e.g., Nowicki & Carton, 1997). Initially, however, the processing of emotional tone of voice and linguistic con- tent do appear to be separate (Kitayama & Howard, 1994). Individuals with left-hemisphere damage often exhibit aphasia or difficulty with the comprehension and/or pro- duction of speech but show relatively less impairment for identifying and producing emotional prosody (Tucker & Frederick, 1989). Conversely, individualswith certain types of right-hemisphere damage have difficulty perceiving, categorizing, and producing emotional prosody but have relatively less impairment in resolving the linguistic struc- ture of language (Bowers, Bauer, & Heilman, 1993). Other areas of the brain, such as the amygdala (Scott et al., 1997) and the hippocampus (Ghika-Schmid et al., 1997), have also been found to play a role in the processing of emotional tone of voice, particularly for negative emotions, such as fear and anger. In normal populations,studies have shown a right-hemisphere advantage for processing tone of voice and a left-hemisphere advantage for processing linguistic content (Buck, 1988; Joanette, Goulet, & Han- nequin,1990; Safer & Leventhal, 1977; Springer & Deutsch, 1998).

Although there appears to be an initial neural separation of the processing of emotional tone of voice and linguistic content, these two sources of information are integrated dur- ing the processing of spoken language. Our appreciation of linguistic devices, such as irony and sarcasm, rests on our ability to evaluate mismatches between linguistic con- tent and prosodic contour. The assumption has been, how- ever, that the integration of these two sources of informa- tion occurs after linguistic processing and the processing of emotional tone of voice have been completed. Conse- quently, current explanations of phonetic perception, lex- ical access, and syntactic parsing, for example, generally include little role for an effect of emotional tone of voice.

Recent research suggests, however, that linguisticprosody may influence both lexical and syntactic processing. Cutler (1994) has found that lexical prosody influences word seg- mentation, lexical activation, and lexical selection. Lexical stress appears to be included in phonological representa- tions of spoken words and appears to help listeners identify word boundaries and to quickly access lexical items in memory. Similarly, Jusczyk, Cutler, and Redanz (1993) have found that infants are sensitive to the prosodic regu- larities of language and appear to use those regularities to initially segment the speech stream. Kjelgaard and Speer (1999) have found that sentential prosody appears to in- fluence listeners’ syntactic parsing behavior in such a way

EMOTION AND LEXICAL AMBIGUITY 585

that linguistic prosody can serve to resolve syntactic am- biguity. These findings suggest that multiple sources of in- formation may be used by listeners to construct and process their initial representations of spoken language. Thus, we may need to expand our analysis of the types of informa- tion that serve to constrain the processing of spoken words. To that end, the present experiments were designed to evaluate whether a nonlinguisticproperty such as emotional tone of voice would influence the resolution of lexical ambiguity.

Emotional tone of voice was selected for study because it appears to be a particularly salient property of spoken lan- guage. A speaker’s tone of voice colors our interpretation of a linguistic message, and listeners appear to interpret a talker’s utterance in the context of the overall tone of voice. Recently, researchers have begun to suggest that emotion, including mood, facial expressions, and emotional tone of voice, may influence language processing (Halberstadt, Niedenthal, & Kushner, 1995; Kitayama,1990, 1991, 1996; Niedenthal & Halberstadt, 1995; Niedenthal, Halberstadt, & Innes-Ker, 1999; Niedenthal & Setterlund, 1994; Nieden- thal, Setterlund, & Jones, 1994). For instance, Kitayama and Howard (1994) found that emotional tone of voice ap- pears to influence the interpretation of sentence-length ut- terances and, in turn, the emotional linguistic content of an utterance appears to influence listeners’ judgments of emotional tone of voice.

With regard to the particular effects of emotional tone of voice on lexical access and selection, research results are mixed. Nygaard and Queen (2002; Nygaard, Queen, & Burt, 1998) found that emotional tone of voice appeared to influence the time course of lexical processing in an emotion-congruentmanner. Nygaard and Queen presented listeners with emotion words produced with congruent, incongruent, or neutral emotional prosody. They found that listeners were faster to name or shadow words that were produced in a congruent tone of voice than those produced in an incongruent or neutral one. Listeners appeared to be integrating the speaker’s tone of voice with linguistic con- tent during spoken word recognition. Conversely, Wurm and Vakoch (1996) found little influence of emotional tone of voice on lexical decision times for words varying in emo- tional connotation.Although they found that the emotional connotation of a word influenced response times, the de- gree to which tone of voice was congruent or incongruent with respect to emotional meaning had little effect on re- sponding.

Across areas of visual and auditory perception, the largest influences of top-down knowledge and context are ob- served when the input to the perceiver is ambiguous. For example, effects of such factors as lexical status or speak- ing rate on phonetic perception are generally found when incoming phonetic information is ambiguous or degraded (Ganong, 1980; Miller & Dexter, 1988; Nygaard, 1993; Samuel, 1996). The present experiments were designed to evaluate whether emotional tone of voice would influence the resolution of lexical ambiguity and the selection of word meaning. We reasoned that in instances in which lex-

ical meaning is ambiguous, as in the case of homophones, we would be most likely to find an influence of context in general and of emotional tone of voice in particular.

Our investigationconsisted of two experiments. In both, listeners were asked to transcribe homophones that had one emotional meaning, either happy or sad, and one neutral meaning (e.g., bridal/bridle, die/dye). Because each homo- phone had a distinct spelling for the alternative meanings, we were able to infer which meaning was accessed from listeners’ transcription performance. In addition,each homo- phone was produced in a happy, sad, or neutral tone of voice. We evaluated whether changing the tone of voice in which a homophone was produced would influence the selection of word meaning. Would the lexical selection process change depending on whether the emotional tone of voice was congruent, incongruent, or neutral with respect to the emotional meaning of each homophone? We predicted that emotional tone of voice would have an emotion- congruent effect on the selection of word meaning. That is, we expected that when the homophones with one happy and one neutral meaning were presented in a happy tone of voice, listeners would provide more happy transcrip- tions than when the homophone was presented in a neu- tral or sad tone of voice. Similarly, we expected that lis- teners would provide more sad transcriptions when the sad/neutral homophones were presented in a sad tone of voice.

EXPERIM ENT 1

The first experiment was designed to determine whether emotional tone of voice would influence the selection of word meaning in lexically ambiguous homophones. Items were presented to listeners blocked by tone of voice, so that listeners heard the happy and sad homophones in only one tone of voice at a time. In this manner, we were able to compare transcription performance for the same ho- mophones presented in each tone of voice. Transcription performance was evaluated because we reasoned that this task would allow us to assess the content and products of lexical resolution. Our aim was simply to determine whether emotional tone of voice, a nonlinguisticproperty of speech, could act as a strong constraint on a linguistic process, lex- ical resolution.

Method Listeners. The subjects were 119 undergraduate students from

Emory University. All were native speakers of American English and reported no known hearing or language disorder at the time of test- ing. They received partial course credit for their participation.

Stimulus materials . A list of 113 words was constructed on the basis of listeners’ ratings of emotional meaning. Test items included emotional homophones that were selected to have one emotional mean- ing ( happy or sad) and one neutral meaning. Filler items included neu- tral homophones with two neutral meanings and words with either a sin- gle emotional ( happy or sad) or a neutral meaning.

Ratings of affective meaning were collected from 23 judges for all emotion-related and neutral homophones and words. Because all the homophones had a distinct spelling for each meaning, ratings of af- fective meaning were collected for one of the spellings from 11 judges

586 NYGAARD AND LUNDERS

and for the other spelling from 12 separate judges. All 23 judges rated the emotional and neutral filler words. The judges were asked to rate each word by using two separate 1- to 7-point Likert-type scales for its relatedness to happiness and for its relatedness to sadness (1, not at all related; 7, highly related ). Word meanings were included accord- ing to the following criteria. Meanings selected as happy were rated at least one standard deviation above the mean for relatedness to happy and one standard deviation below the mean for relatedness to sadness. The opposite criteria were used for selecting sad meanings. Neutral meanings had ratings below the mean for both the happiness and the sadness scales. Happy homophones (n = 12) had one mean- ing rated as happy and one rated as neutral, using the above criteria. Sad homophones (n = 10) had one meaning rated as sad and one as neutral. Both meanings were rated as neutral for neutral homo- phones (n = 9). An additional 4 happy homophones were taken from Halberstadt et al. (1995), resulting in a total of 16 happy homo- phones. Filler words had a single meaning rated as happy (n = 28), sad (n = 21) or neutral (n = 29). Mean word frequency for the emo- tional meanings of happy and sad homophones did not differ signif- icantly from the mean frequency of their neutral counterparts. In ad- dition, mean word frequency for the happy, sad, and neutral filler words did not differ significantly from one another. Table 1 shows the mean ratings of relatedness to happy and sad for both meanings of the emotional homophones. The Appendix lists all the homophones and filler items used in this study.

All 113 words were recorded in each of three different tones of voice ( happy, sad, and neutral) by one female and one male amateur actor. Words were read in random order in one tone of voice at a time. The actors were instructed to enunciate clearly, read at a comfortable rate, and not allow the meaning of the word to influence the tone of voice. Both spellings of the homophones were provided in order to discourage the speakers from pronouncing them differently depend- ing on meaning. All the stimuli were digitally recorded in a sound- attenuated room with a Sony Digital Audio Tape-corder TCD-D7. Each stimulus item was redigitized on a PowerMac 7100/ 80 at

22.050-kHz sampling rate and was edited into separate files for pre- sentation.

To confirm that the tone of voice manipulation was perceptually salient, tone of voice judgments were collected for all the stimuli. Thirty-six listeners were presented all 113 stimulus items in each of the three emotional tones and were asked to judge the tone of voice ( happy, neutral, or sad) of each word. The words were presented in- dividually in random order, and the listeners were instructed to ig- nore word meaning and to respond solely to the tone of voice. Any stimulus from either speaker that did not reach the criterion of 75% correct tone-of-voice judgments, averaged across listeners, was rere- corded, redigitized, and edited for presentation.

To confirm that the speakers did not pronounce the words differ- ently depending on meaning, acoustic measurements were taken of each homophone in each tone of voice. Presumably, pronunciation of the homophones could differ, depending on the relationship be- tween meaning and tone of voice. For example, speakers might have pronounced happy homophones in a “happier” tone of voice than they pronounced neutral or sad homophones. To ensure that this was not the case, duration, fundamental frequency (F0), F0 variation, and root-mean square (RMS) amplitude were measured for words in each condition and are shown in Table 2. Separate analyses of vari- ance (ANOVA) were conducted for each acoustic measurement. Ho- mophone type ( happy, neutral, and sad) and tone of voice ( happy, neutral, and sad) were factors. Each analysis revealed significant main effects only of tone of voice [duration, F(2,200) = 42.39, p < .001; F0, F(2,200) = 13.94, p < .001; F0 standard deviation, F(2,200) = 29.27, p < .001; RMS amplitude, F(2,200) = 7.93, p < .001], indi- cating that each acoustic measure varied as a function of tone of voice. Main effects of meaning and interactions of tone of voice and meaning were not significant, indicating that the acoustic measures did not reliably differ as a function of meaning. Thus, the strength of the tone of voice manipulation appeared to be roughly comparable across homophone types.

Procedure. Homophone type ( happy or sad) was manipulated as a within-subjects factor. Emotional tone of voice ( happy, sad, or neu- tral) and the voice of talker (male or female) were manipulated as between-subjects factors. Each group of listeners was presented with the list of 113 words in only one tone of voice. Thirty-nine lis- teners heard the happy tone of voice, 40 listeners served in the sad tone-of-voice condition, and a separate group of 40 listeners served in the neutral tone-of-voice condition. Within each tone-of-voice condition, approximately half of the listeners were presented with the list produced by the male talker, and half were presented with the list by the female talker. Talker was manipulated to control for any effects of talker-specific idiosyncrasies.

The listeners were individually tested in a sound-attenuated room. The stimuli were presented binaurally over matched and calibrated

Table 1 Mean Ratings of Relatedness to Happy and Sad

Emotional Homophones Happy Sad

Happy (e.g., flower/flour) happy meaning 4.05 1.39 neutral meaning 1.58 1.19

Sad (e.g., die/dye) sad meaning 1.29 4.51 neutral meaning 1.44 1.32

Neutral (e.g., hair/hare) 1.36 1.18

Table 2 Acoustic M easurem ents of Each Homophone Type

Produced in Each Tone of Voice Condition

Homophone Type

Acoustic Measure Tone of Voice Happy Neutral Sad

Duration (msec) happy 745.12 714.13 706.68 neutral 578.63 512.11 551.73 sad 824.40 847.91 802.08

F0 (Hz) happy 203.15 208.12 203.08 neutral 192.97 191.74 192.40 sad 182.62 176.83 186.66

F0 standard deviation (Hz) happy 31.81 34.04 34.49 neutral 27.92 25.70 22.27 sad 19.69 21.39 19.31

Root-mean square amplitude (volts) happy .526 .631 .689 neutral .537 .552 .650 sad .452 .456 .436

EMOTION AND LEXICAL AMBIGUITY 587

Beyerdynamic DT100 headphones at approximately 75 dB (SPL). Stimulus presentation and data collection were controlled on line, using PsyScope (Cohen, MacWhinney, Flatt, & Provost, 1993) on a PowerMac 7100/80 computer. During the experiment, the words were presented in random order, and the listeners were instructed to type the word that they heard on the keyboard in front of them. After typing in their response, they were instructed to hit the return key to initiate the next trial. If the listeners did not respond within 4 sec, the next trial was automatically initiated. No information was given to the listeners about the presence of homophones. After the experi- ment was completed, the listeners were asked (1) whether they no- ticed the presence of homophones, (2) how many homophones they remembered hearing, (3) whether they noticed that some homo- phones had emotional meanings, (4) how they chose which spelling to report, and (5) whether they had ever started typing one spelling but then changed their minds. These questions were designed to de- termine whether the listeners were responding strategically on the basis of the demands of the experimental situation.

Because each meaning of the homophone had a unique spelling, it was assumed that the listeners had accessed the emotional mean- ing if they produced the emotional spelling. Likewise, if the listeners produced the neutral spelling, it was assumed that they had accessed the neutral meaning. Percentage of emotional transcriptions served as the dependent measure.

Results and Discussion Figure 1 shows percentage of affective transcriptions, col-

lapsed across speaker, plotted as a function of homophone type ( happy/neutral and sad/neutral) and tone of voice. As the figure shows, the listeners were more likely to provide the happy transcription of the happy/neutral homophones when the words were produced in a happy tone of voice.

Likewise, the listeners provided more sad transcriptions of the sad/neutral homophones when they were produced in a sad tone of voice.

A 2 3 3 ANOVA, with homophone type ( happy/neutral and sad/neutral) and tone of voice ( happy, neutral, and sad) as factors, was conducted using percentage of emo- tional transcriptions, collapsed across speakers, as the de- pendent measure. The analysis revealed a significant main effect of homophone type [F (1,116) 5 35.95, p , .0001], indicating that, overall, the listeners produced more affec- tive transcriptions (relative to neutral transcriptions) for the sad homophones than for the happy homophones. As was predicted, the analysis also revealed a significant in- teraction between homophone type and tone of voice [F (2,116) 5 10.19, p , .0001], indicating that the num- ber of affective transcriptions varied as a function of emo- tional tone of voice. Post hoc Tukey’s HSD comparisons revealed that, for happy/neutral homophones, the percent- age of happy transcriptions was significantly greater in the happy tone of voice than in the neutral or sad tone of voice ( p , .05). For sad/neutral homophones, the per- centage of sad transcriptions was significantly greater in the sad tone of voice than in the neutral or happy tone of voice.

The listeners’ responses after the experiment suggest that they were not responding strategically to the demands of the experimental task. In response to the question of whether they noticed the presence of homophones, all the listeners stated that they were aware of homophones. The

Figure 1. Percentages of affective transcriptions are plotted as a function of homophone type and tone of voice for the blocked tone-of-voice conditions of Experiment 1.

588 NYGAARD AND LUNDERS

number of homophones they reported varied from 5 to 40. However, none of the listeners reported noticing that some of the homophones had emotional meanings. Ninety per- cent of the listeners indicated that they chose whichever spelling came into their mind first. However, 7% of the listeners indicated that the words preceding the homo- phone influenced which spelling they chose. Only 3 listen- ers mentioned that they started typing one spelling and changed it to the other. The listeners’ responses indicated that although they appeared, in general, to be aware of ho- mophones in the test list, they were not aware of meaning/ tone-of-voice correspondences. Given that they did not re- port noticing homophones with one emotional and one neutral meaning, it is unlikely that they were responding to the explicit demand characteristics of the experiment.

These results indicate that the listeners were more likely to select the meaning of an ambiguous word that was con- gruent with the emotional tone of voice in which the word was produced. This finding suggests that the listeners not only were sensitive to the emotional tone of voice of the speaker, but also were integrating that tone of voice with the linguistic content of each word. The listeners appeared to use the emotional tone of voice to disambiguate the meaning of the emotional homophones. This finding is similar to Halberstadt et al.’s (1995) finding that listeners were more likely to choose an emotional meaning of an ambiguous homophone that was congruent with their in- duced mood. These findings are consistent with the view that listeners may be using emotional tone of voice as a type of context in which to guide their lexical selection.

Although emotional tone of voice appears to guide lex- ical selection, there are several ways in which it could have influenced the word recognition process. Because tone of voice was manipulated as a between-subjects factor, the listeners may not necessarily have been integrating tone of voice with their lexical processing of each word. Rather, the listeners may have adopted a general perceptual set consistent with the prevailing tone of voice and used it to guide lexical selection. This perceptual set could be either a general emotional expectation or even an induced mood resulting from a constant unvarying tone of voice. To eval- uate these possibilities, the second experiment manipu- lated tone of voice as a within-subjects factor. From trial to trial, not only emotional meaning, but also emotional tone of voice varied. Thus, on any given trial, not only were the subjects unable to predict whether the meaning of each word was congruent, incongruent, or neutral with respect to tone of voice, but also they were unable to predict which tone of voice would be presented. The variation from trial to trial in tone of voice was assumed to prevent the devel- opment of a perceptual set or mood by the listeners. We pre- dicted that tone of voice would influence the selection of word meaning in the absence of a perceptual set or mood.

EXPERIMENT 2

Method Listeners. The subjects were 45 undergraduate students from

Emory University. All were native speakers of American English and

reported no known hearing or language disorder at the time of test- ing. They received partial course credit for their participation.

Stimulus materials . Stimulus materials were the same 113 words as those used in Experiment 1. However, given the similar pattern of performance for the two speakers in the first experiment, only the fe- male speaker’s utterances were used. Three lists were constructed in which approximately one third of the happy, neutral, and sad homo- phones (and each type of filler word) was presented in a happy tone of voice, one third in a neutral tone of voice, and one third in a sad tone of voice. Lists were counterbalanced so that homophones were rotated through each tone of voice condition. Thus, across listeners, a given homophone was heard in each tone of voice.

Procedure. Homophone type ( happy or sad) and emotional tone of voice were manipulated as within-subjects factors. Each group of 15 listeners was presented with one of the three counterbalanced lists of 113 words. Order of stimuli was randomized so that tone of voice and type of homophone varied from trial to trial. All other aspects of method and procedure were identical to those in the first experi- ment.

Results and Discussion Figure 2 shows percentage of affective transcriptions

plotted as a function of homophonetype ( happy/neutral and sad/neutral) and tone of voice. The listeners appeared more likely to produce the happy transcription of the happy/ neutral homophones when the words were produced in a happy tone of voice and to provide more sad transcriptions of the sad/neutral homophones produced in a sad tone of voice.

A 2 3 3 ANOVA, with homophone type ( happy/neutral and sad/neutral) and tone of voice ( happy, neutral, and sad) as factors, was conducted using percentage of emo- tional transcriptions as the dependent measure. The analy- sis revealed a significant main effect of homophone type [F(1,44) 5 9.94, p , .005], indicating that, overall, the listeners produced more affective transcriptions (relative to neutral transcriptions) for the happy homophones than for the sad homophones. This finding reflects the fact that the listeners produced more happy transcriptions, overall, for the female speaker and is consistent with the results of the first experiment. It is possible that the female speaker may have had, in general, a positive vocal affect, resulting in fewer sad and more happy transcriptions.

The analysis also revealed a marginally significant in- teraction between homophone type and tone of voice [F(2,88) 5 2.95, p , .06], indicating that the number of affective transcriptions varied as a function of emotional tone of voice. Post hoc Tukey’s HSD comparisons revealed that for happy/neutral homophones, the percentage of happy versus neutral transcriptions did not differ signifi- cantly across tone-of-voice conditions. For sad/neutral ho- mophones, however, the percentage of sad versus neutral transcriptions was significantly greater in the sad tone-of- voice condition than in the neutral or happy tone-of-voice condition ( p , .01).

Effect size estimates were calculated for the significant interactions in Experiments 1 and 2 between tone of voice and homophone type. In the first experiment, the interac- tion term accounted for approximately 17% of the vari- ance (estimated v 2 5 .17). In the second experiment, the interaction between these two factors accounted for ap-

EMOTION AND LEXICAL AMBIGUITY 589

proximately 4% of the variance (estimated v 2 5 .04). Ac- cording to Cohen’s (1977) suggestions, the effect size for the interaction in the first experiment was fairly large, whereas the effect size in the second experiment was more moderate.

These findings suggest that although the effect of tone of voice was somewhat attenuated, relative to the first ex- periment, tone of voice did significantly influence the num- ber of emotional transcriptions that the listeners produced. In particular, the listeners reliably chose the sad spelling of sad/neutral homophones when produced in a sad tone of voice. The difference between happy and sad emotions in this experiment has also been found in other tasks and domains. For example, Halberstadt et al. (1995) found, in a mood induction paradigm, that subjects provided more sad than neutral spellings for sad homophones when a sad mood was induced. However, subjects did not provide more happy than neutral spellings for happy homophones when a happy mood was induced. The reason for this asymmetry is unclear, but it is possible that our sad homo- phones in particular or sad emotional content in general were more salient or distinct from neutral content than were our happy homophones or happy emotional content in gen- eral. Despite the asymmetry, however, this finding does suggest that the listeners were not just adopting a percep- tual set or developing a mood that was congruent with a particular tone of voice but, rather, that listeners appeared to use the emotional tone of voice of individual words to influence their lexical selection.

GENERAL DISCUSSIO N

In the present study, we investigatedthe role of emotional tone of voice in the resolution of lexical ambiguity. Two experiments were conducted in which listeners were asked to transcribe homophones that had both an affective and a neutral meaning. The homophones were presented with emotional prosody that was congruent, incongruent, or neutral with respect to the affective meaning. In the first experiment, tone of voice was blocked so that each group of listeners heard each type of homophone ( happy and sad) in only one tone of voice ( happy, sad, or neutral). In the second experiment, tone of voice was manipulated within subjects so that the listeners heard both types of ho- mophones presented in all three affective tones. We found that, across experiments, the listeners provided more emo- tional transcriptions when the homophones were pre- sented in a congruent tone of voice, as opposed to a neu- tral or incongruent tone of voice. These results suggest that the listeners selected meanings of ambiguous words that were congruent with the nonlinguistic properties of the speakers’ utterances. Emotional tone appears to have been integrated during linguistic processing to constrain the listeners’ selection of word meaning.

Voice expression was also shown to be related to word meaning in an experiment conducted by Kunihira (1971). They found that English-speaking listeners were better able to guess the meaning of Japanese antonyms when the words were produced with an expressive voice than when

Figure 2. Percentages of affective transcriptions are plotted as a function of homophone type and tone of voice when tone of voice was mixed in Experi- ment 2.

590 NYGAARD AND LUNDERS

the words were read in a monotone or were presented vi- sually. Taken together with our results, this finding suggests that tone of voice or emotional prosody not only may guide the selection of familiar lexical meaning, but also may be used to infer meaning from unfamiliar items. Listeners may use voice expressiveness or tone of voice in a man- ner similar to sentential context to constrain possible lex- ical candidates and to derive meaning from unfamiliar or noisy signals.

Although emotional tone of voice influenced lexical pro- cessing, it did not completely constrain the listeners’ selec- tions. In both experiments, the listeners still provided neu- tral transcriptions a certain percentage of the time. This finding suggests that emotional tone of voice may act as one of many possible constraints on lexical selection. Var- ious constraints, such as the particular frequency of oc- currence of a given word meaning (see Simpson, 1994, for a review of constraints on the resolution of lexical ambi- guity), may each contribute differentially to the lexical ac- tivation and selection process to result in each listener’s ultimate selection. For example, in the case of our emotional homophones, although mean word frequency was equated across emotional and neutral meanings, for any given ho- mophone, one meaning may have been more frequent. In cases in which the neutral meaning was higher in fre- quency than the emotional meaning, it may have been more difficult to demonstrate an influence of emotional tone of voice. Just as is the case with sentential or linguistic seman- tic content, word frequency may have interacted with the effects of emotional tone of voice.

This finding that emotional tone of voice did not com- pletely constrain transcription performance also suggests that tone of voice may serve as a somewhat weaker con- straint than does sentential context during lexical process- ing. Given the off-line nature of our task, one would as- sume that any effects of a constraining context would have had plenty of time to be integrated with on-going lexical processing, at the activation, selection, or decision stages. That listeners still provided neutral transcriptions some of the time suggests that even in congruent tone-of-voice conditions, listeners still had the neutral meaning avail- able at the time of transcription. In cross-modal priming tasks, research suggests that after as little as 600 msec, only the meaning that is consistent with a constraining sentential context is still activated (e.g., Paul et al., 1992). Although numerous differences exist between the pro- cessing demands of cross-modal priming and the current transcription task, emotional tone of voice does appear to influence lexical selection either in a different manner or to a different degree than does sentential context.

One way in which emotional tone of voice might influ- ence lexical selection is that it may be preserved, along with linguistic content, in some kind of integrated lexical rep- resentation. For these homophones,the same phonological form points to two meanings, one emotional and one neu- tral. However, if tone of voice is preserved in memory and is correlated with a particular meaning in the listener’s ex- perience, listeners should choose the orthographic repre- sentation that reflects a consistent pairing of tone of voice

with a particular meaning. For example, for a happy homo- phone, a happy tone of voice may occur more often with the happy meaning than with the neutral meaning. Conse- quently, when the homophone is encountered in a happy tone of voice, the probability of accessing the happy mean- ing becomes greater.

This view has much in common with Goldinger’s (1998) exemplar-based view. Goldinger (1998) suggested that spoken word recognition is based on an episodic lexicon. Aspects of a spoken word, such as a talker’s voice and the context in which it occurs, were hypothesizedto be included in the memory trace of every word. Each word is repre- sented by a collection of instance-specific memory traces. On this view, perceptual and other characteristics of spo- ken words, such as voice and accompanying context, could all potentially contribute to the lexical access and retrieval process. On the basis of Hintzman’s (1986, 1988) multiple-trace memory model, Goldinger’s (1998) theory suggests that a to-be-recognized lexical item or probe ac- tivates a set of similar traces in memory. The intensity or strength of the activation, or echo, depends on the simi- larity of the probe to existing traces and to the number of traces in memory. If memory traces for words include such properties as voice identity or emotional tone, these properties, under the right circumstances, should influ- ence lexical access and spoken word recognition.

In a series of experiments , Goldinger (1998) found that listeners’ shadowing times, as well as the shadowing ut- terances themselves, reflected voice-specific properties of spoken words. For example, listeners’ shadowing utter- ances mimicked the perceptual characteristics and, pre- sumably, the acoustic characteristics of the spoken words that were shadowed. Furthermore, as the number of times an item was repeated in the same voice increased, the de- gree to which the shadowing utterance matched the orig- inal speaker’s production increased as well. Within the conceptual framework of the model, when an item is re- peated with the same voice, many traces will be created with those particular talker characteristics. When a probe with the same voice is subsequently presented, the simi- larity of the probe to a number of existing traces will be high, resulting in shadowing responses that preserve talker-specific characteristics.

With respect to homophones or words with multiple senses, Hintzman (1986) suggests that these types of items may be represented by nonoverlappingcollectionsof mem- ory traces. Each meaning of a homophone is hypothesized to be highly context dependent, so that only a context- appropriate sample of the memory traces for any given word form will be activated during processing. According to this view and Goldinger’s (1998) theory and findings, it is possible that if spoken words are represented as instance- specific memory traces, homophonesthat had one emotional and one neutral meaning might have different nonverbal or tone-of-voice characteristics associated with each sep- arate meaning. The emotional meaning of a homophone would have been previously encountered in specific con- texts with a congruent emotional tone of voice. Encoun- ters with the neutral meaning would be more variable with

EMOTION AND LEXICAL AMBIGUITY 591

respect to tone of voice. This view is consistent with our data and suggests that aspects of a spoken utterance, such as context and voice characteristics, are preserved in memory, along with linguistic content. Thus, the effects of emotional tone of voice on lexical processing do not result from a top-down or a postprocessing influence, but rather emerge as a direct consequence of the nature of lexical representation and memory retrieval.

An alternative possibility is that emotional tone of voice may act as a kind of semantic context during the selection of word meaning. According to this view, emotional tone of voice is perceived and processed separately from lin- guistic content but is integrated relatively early in the pro- cessing of spoken words. Although this task does not allow us to pinpoint precisely the stage at which emotional tone of voice is integrated, it does at least appear that tone of voice influences the lexical selection and decision stages of linguistic processing. Certainly, other research suggests that nonlinguistic properties of speech (e.g., Goldinger, 1998) and, in particular, emotional tone of voice (Nygaard & Queen, 2002) influence the time course of lexical pro- cessing. Consequently,tone of voice may serve to activate emotion-congruent representations in memory, thereby facilitating and influencing the processing of spoken words.

How emotional meaning is extracted and how emotion is represented in memory remains unclear. Some accounts suggest that emotion is represented categorically, so that particular primary emotions, such as happiness, sadness, or anger, constitute independent category structures (e.g., Bower, 1981, 1987; Niedenthal et al., 1999). Alternative accounts suggest that emotion is represented as values along continuous dimensions, such as valence ( positive vs. negative) and/or arousal ( high vs. low) (e.g., Feldman, 1995; Lang, Bradley, & Cuthbert, 1990). With respect to emotional displays, such as tone of voice, listeners may be either extracting primary categorical emotional content or, rather, evaluating tone of voice in terms of a dimensional analysis. Our stimuli were designed to be neutral with re- spect to these views. Our happy versus sad distinction maps onto a positive versus negative one. Nevertheless, in other studies in which the influence of emotion on aspects of cognition and perception was investigated, emotion ap- pears to act in a category-specific manner (see Niedenthal et al., 1999).

In addition to the direct effects of tone of voice on lex- ical selection, there may also have been a more indirect influence of emotional tone of voice. Although the pat- terns of results across experiments were comparable, there did appear to be a somewhat larger effect of tone of voice in the blocked design than in the mixed design. Thus, in the first experiment, in addition to integrating tone-of-voice information with linguistic content, listeners may have been developinga perceptual set or expectation.The blocked design allowed the listeners both to fully perceive and to identify the particular tone of voice and to set up a set of expectations about the surface form of the next to-be- transcribed word. When no such set or expectation could be developed, as in the mixed presentation format of the

second experiment, the listeners were forced to reinterpret tone of voice on each trial, potentially leading to a some- what attenuated effect of tone of voice. Interestingly, ef- fects of a generally accepted lexical property, word fre- quency, also appear to be susceptible to differences in mixed versus blocked designs. For example, Whalen and Wenk (1993) reported that when homophones were read aloud, low-frequency spellings resulted in longer utter- ances, but only when blocked low-frequency and high- frequency lists were presented.

Although these experiments strongly suggest that emo- tional tone of voice constrains the lexical selection process, there are potential limitations to this study. One is that the listeners may have been sensitive to the demand charac- teristics of the task. They may have recognized that the words had alternative meanings that varied with respect to the speaker’s tone and may have altered their responses ac- cordingly. Aspects of the data argue against this conclu- sion. First, in Experiment 1, the listeners did not report noticing emotional homophones in the test list. Rather, the majority of listeners reported transcribing the first spelling that came to mind. Although not conclusive, these reports strongly suggest that the listeners did not recognize alter- native meanings of the homophones and then respond ac- cordingly. Second, if the listeners had noticed that our test list was studded with emotional homophones, we might have expected an overwhelming effect of tone of voice, limited only by the listeners’ ability to perceive emotional prosody and identify the alternative meanings of the ho- mophone. Given the number of nonhomophone distrac- tors and given the graded nature of our effects, it seems likely that transcription performance reflected a real in- fluence of tone of voice on the lexical selection process.

In summary, these findings call into question traditional accounts of spoken language processing. The linguistic system and, in particular, lexical access and spoken word recognition do not appear to be isolated from other types of auditory information. Nonlinguistic properties of speech are not necessarily irrelevant with respect to lexical pro- cessing. Rather, nonlinguisticaspects of spoken language, such as emotional tone of voice, appear to be highly rele- vant aspects of spoken language that are integrated into linguistic processing. Emotional tone of voice may act as one type of contextual constraint in lexical access and se- lection, either by virtue of its pairing with particular mean- ings or because listeners actually extract emotional mean- ing from tone of voice and then integrate it with linguistic content. This influence of emotional tone of voice suggests that current accounts of the nature of contextual constraints in the resolution of lexical ambiguity need to be reconsid- ered. Both linguistic and nonlinguistic properties, such as emotional tone of voice, appear to work together to con- strain the eventual access and selection of word meaning.

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APPENDIX Emotional Homophones With Emotion Meaning Listed First and

Neutral Homophones

Happy Sad Neutral ate/eight banned/band chews/choose bridal/bridle blue/blew chord/cord caller/collar bored/board pair/pear dear/deer die/dye hair/hare flower/flour groan/grown hall/haul heal/heel lone/loan pause/paws hymn/him pain/pane heard/herd knows/nose poor/pour/pore meat/meet medal/metal thrown/throne toe/tow peace/piece missed/mist petal/pedal presents/presence rose/rows sweet/suite tide/tied won/one

Filler Words

award lucky ache shame border pottery beauty nice blame sorrow chair pump cash paradise cancer struggle cycle rice charm praise crisis upset detect rock cheer prize depressed worse display sheet comedy proud disappoint fence sleeve dazzle safe distress formula soap enjoy smile empty habit spare flourish sunny failed handle stamp friend triumph gloomy label uniform funny trust grave locate switch glad utopia injury marble trace glory losing margin track humor morgue noon kiss poverty panel laugh regret phone

(Manuscript received May 12, 2000; revision accepted for publication January 24, 2002.)