Atten Percept Psychophys (2014) 76:11–18 DOI 10.3758/s13414-013-0600-4
Famous talker effects in spoken word recognition Alisa M. Maibauer & Teresa A. Markis & Jessica Newell & Conor T. McLennan
Published online: 24 December 2013 # Psychonomic Society, Inc. 2013
Abstract Previous work has demonstrated that talkerspecific representations affect spoken word recognition relatively late during processing. However, participants in these studies were listening to unfamiliar talkers. In the present research, we used a long-term repetition-priming paradigm and a speeded-shadowing task and presented listeners with famous talkers. In Experiment 1, half the words were spoken by Barack Obama, and half by Hillary Clinton. Reaction times (RTs) to repeated words were shorter than those to unprimed words only when repeated by the same talker. However, in Experiment 2, using nonfamous talkers, RTs to repeated words were shorter than those to unprimed words both when repeated by the same talker and when repeated by a different talker. Taken together, the results demonstrate that talkerspecific details can affect the perception of spoken words relatively early during processing when words are spoken by famous talkers. Keywords Spoken word recognition . Specificity effects . Variability . Time course . Famous talkers . Attention . Priming . Lexical representation and processing A major issue in various areas of cognitive science is determining the nature of mental representations. This issue has been manifested as debates over general versus specific representations. In the present study, we focused on talker variability and its representational implications for spoken word recognition. T. A. Markis : J. Newell : C. T. McLennan (*) Language Research Laboratory, Department of Psychology, Cleveland State University, 2300 Chester Avenue, Cleveland, OH 44115, USA e-mail: [email protected] A. M. Maibauer Department of Internal Medicine, Virginia Commonwealth University, Richmond, VA, USA
Researchers from psychology, linguistics, and related domains have examined the role that variability in surface information (e.g., change of talkers) plays in listeners’ ability to recognize spoken words, as a way to investigate the nature of the representations in the mental lexicon. The focus in the present study is determining whether talker-independent (abstract) or talker-specific (episodic) lexical representations affect listeners’ perception of words spoken by famous talkers. In order to investigate this issue, we used the long-term repetition-priming paradigm in which stimuli are presented in two blocks, separated by a distractor task. If priming is unaffected by a talker change, such that “people” spoken by Talker A is primed equally well by Talker A or Talker B, then an abstract representation is presumably accessed. If, however, priming is attenuated by a talker change (a talker effect), such that “people” spoken by Talker A is only (or more) primed by Talker A, then an episodic representation is presumably accessed. Previous long-term repetition-priming research has shown that talker changes can affect processing under certain conditions (Schacter & Church, 1992). The overwhelming majority of previous studies have been conducted with unknown talkers (Bradlow, Nygaard & Pisoni, 1999; Goldinger, Pisoni & Logan, 1991; Martin, Mullennix, Pisoni & Summers, 1989; Mullennix, Pisoni & Martin, 1989). While these studies have undoubtedly advanced our understanding of representational and processing issues in spoken language, we still know relatively little about the nature of representations for words produced by familiar talkers. There is evidence that language produced by familiar talkers is stored and processed differently than language produced by unknown talkers. In particular, the right hemisphere may play a special role for familiar voices (and familiar faces, names, etc.; Van Lancker, 1991). Furthermore, there is evidence that listeners are faster to shadow words produced by familiar talkers than those produced by unfamiliar talkers (Nygaard, Sidaras & Alexander, 2008).
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According to abstractionist theories, talker information is discarded through a normalization process (Pisoni, 1997), and lexical representations are void of talker-specific details (McClelland & Elman, 1986). According to episodic theories, multiple traces are stored, which include our experience hearing the same word produced by different talkers (Goldinger, 1997). While both theoretical approaches are able to account for some of the results, a clearer picture emerges when the theories are integrated into a hybrid account (Goldinger, 2007). Consequently, rather than debating between abstract and episodic representations, the emphasis is now on determining the circumstances under which each type of representation is more or less likely to affect listeners’ perception of spoken words (McLennan, 2007). At least two such circumstances have been identified. First, there is evidence that episodic (talker-specific) information is located in the right hemisphere and abstract (talkerindependent) information is stored in the left hemisphere (González & McLennan, 2007; Marsolek & Burgund, 2008; Van Lancker, 1991; Van Lancker, Cummings, Kreiman & Dobkin, 1988). Second, there is evidence that lack of (or attenuated) priming for words repeated by a different talker is more likely when processing is relatively slow. According to the time-course hypothesis, abstract information affects processing early, and prior to any effects of talker-specific representations (Luce & Lyons, 1998; McLennan & Luce, 2005). Although there is mounting evidence in support of this time-course hypothesis (Mattys & Liss, 2008; McLennan & González, 2012; McLennan & Luce, 2005; Vitevitch & Donoso, 2011), all of these studies used stimuli produced by talkers that were unknown to the participants. We conducted two experiments to test whether the predictions of the time-course hypothesis are limited to perceiving words produced by unknown talkers. To do so, we investigated potential differences in talker effects, depending on whether the words were spoken by famous (Experiment 1) or nonfamous (Experiment 2) talkers. In both experiments, in order to encourage relatively fast processing, we used the speeded-shadowing task, in which participants are instructed to shadow (or repeat) a spoken word as quickly and accurately as possible. Previous work with nonfamous talkers found no talker effects using the speeded-shadowing task, when processing was relatively fast, and found that talker effects emerged when a delayed-shadowing task was used (McLennan & Luce, 2005). Because words are recognized more quickly when produced by familiar talkers (Nygaard et al., 2008; Nygaard, Sommers & Pisoni, 1994), no talker effects should emerge. More specifically, assuming that the time-course hypothesis generalizes to famous talkers, then in both Experiments 1 and 2, responses to repeated words would be expected to be faster than responses to unprimed words, both when repeated by the same talker and when repeated by a different talker, and there
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should be no difference between the same- and different-talker conditions (i.e., no talker effects). However, if the predictions of the time-course hypothesis are indeed limited to perceiving words spoken by unknown talkers, then perhaps talker effects will emerge with famous talkers, despite relatively fast processing. More specifically, in Experiment 1 (with famous talkers), but not in Experiment 2 (with nonfamous talkers), responses to repeated words would be expected to be faster than responses to unprimed words only when repeated by the same talker, and responses in the same-talker condition should be faster than responses in the different-talker condition (i.e., talker effects in Experiment 1, but not in Experiment 2). The familiar talker stimuli used in previous research are almost always unknown to the participants before the experiment. Participants undergo a familiarization process where they learn to identify the talkers that appear later during the experiment. In the present research, we investigated the processing of words spoken by talkers already familiar to the participants prior to the study. The present study (1) extends time-course predictions to the perception of words spoken by famous talkers, (2) adds to our understanding of the role that talker variability plays in listeners’ perception of spoken words and, thereby (3) contributes to the important theoretical issue of representational specificity, and (4) is the first to investigate possible differences in specificity for words spoken by famous and nonfamous talkers.1
Experiment 1: Famous talkers Method Participants Forty-two participants recruited from the Cleveland State University community participated. Participants received either participation credit toward a class requirement or extra credit. Participants were right-handed, native speakers of American English, with no reported history of speech or hearing disorders. Materials The stimuli consisted of 24 bisyllabic experimental words and 8 bisyllabic filler words (Appendix 1), all of which were spoken by Barack Obama (BO) and Hillary Clinton (HC). Stimulus words were extracted from CSPAN press conference videos (Appendix 2) using RealPlayer v.11. The audio was extracted with FFmpeg, an open-source multimedia converter. Final stimuli were prepared, and mean amplitudes were 1 The majority of past research involving famous talkers has focused on participants’ abilities to recognize and name famous voices.
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equated, using PeakPro audio editing software. The 24 experimental words had a mean frequency of 313.1 (Kučera & Francis, 1967), and a mean duration of 505 ms (SD = 108 ms). The durations of the stimuli produced by BO (466 ms; SD = 81 ms) were significantly shorter than the durations of the stimuli produced by HC (544 ms; SD = 118 ms), t(46) = 2.65, p = .01. The experimental stimuli underwent an initial screening test to ensure that participants were able to accurately perceive these words extracted from sentence contexts. On average, the stimuli were accurately identified by more than 9 out of the 10 screening participants.
13 Table 1 Experimental conditions and examples Condition Match BO prime→BO target HC prime→HC target Mismatch BO prime→HC target HC prime→BO target Control Unrelated prime→BO target Unrelated prime→HC target
Prime
Target
people BO people HC
people BO people HC
people BO people HC
people HC people BO
(one of the filler words)BO people BO (one of the filler words)HC people HC
Design 2
Two blocks (prime and target) of stimuli were presented. Stimuli for these blocks consisted of the words spoken by BO and HC. Participants were not told the identities of the talkers in advance, or even that they would be hearing famous talkers.3 In both blocks, half the stimuli were spoken by BO, and half by HC. As is illustrated in Table 1, the three types of prime–target pairings were (1) match (same word, same talker), (2) mismatch (same word, different talkers), and (3) control (the word was replaced by an unrelated filler word and did not appear in the prime block). Each of the two blocks consisted of 24 stimuli, eight words in each of the three conditions. The stimuli were counterbalanced such that every word appeared in every condition, and no participant heard a word more than once within a block. Procedure Participants were tested individually in a quiet room and were not told at the beginning of the experiment that there would be two blocks. Participants performed a speeded-shadowing task in which they were instructed to repeat each word as quickly and accurately as possible. After the participants responded, the next trial began. All words were presented binaurally over a headset with SuperLab 4.0.7b software (Cedrus Corporation, 2006) for Mac OSX. To familiarize the participants with the task, 10 practice trials were presented. Participants’ reaction times (RTs), measured from stimulus onset, were recorded with a microphone placed approximately 2
The design and procedure followed Experiment 3A of McLennan and Luce’s (2005) study. 3 Presumably, the magnitude of the effect would be larger if participants were given this information in advance. However, we specifically sought to investigate talker effects with famous talkers without explicitly drawing participants’ attention to the talkers. Furthermore, participants were given a postshadowing questionnaire in which, after being informed of the identities of the talkers, they were asked to indicate their political affiliation, level of interest in politics, and other such information (all of which is reported in Maibauer, 2009). There were no significant relationships of interest between the responses on the questionnaire and the magnitude of the obtained talker effects.
1 in. from their lips that was attached to a SuperLab SV-1 voicekey. To verify accuracy, participants’ responses were recorded with Praat software (Boersma, 2001). Participants were given a math test filler task for approximately 5 min between the prime and target blocks.
Results One participant was excluded due to having a priming effect value (match RT minus control RT) that fell two standard deviations beyond the grand priming effect mean. RTs were excluded if they were less than 200 ms or greater than 2,000 ms,4 resulting in the exclusion of 26 RTs (2%). Mean percentage correct (PC) was 99%.5 We performed a 3 (prime: match, mismatch, control)×2 (talker during the target block: BO, HC) repeated measures ANOVA on the RTs to correct responses. The prime×talker interaction was not significant, F (2, 80) < 1.0, p = .88, η p2 = .003. We observed a main effect of talker, F(1, 40) = 27.13, p < .001, η p2 = .40, indicating faster RTs to BO than to HC, presumably due to the duration difference. We observed a main effect of prime, F (2, 80) = 3.30, p = .04, η p2 = .08. Planned comparisons consisting of paired one-tailed t-tests6 4
RT exclusionary criteria in the speeded-shadowing task followed McLennan and Luce’s (2005) exclusionary criteria. 5 Eighteen (43%) of the participants were able to identify at least one of the famous talkers (HC, n = 13; BO, n = 18). Regardless of whether or not participants were able to identify the talkers, it is highly probable that all participants had been exposed to these particular talkers before the experiment and were aware that they were hearing famous voices. Unfortunately, participants were not asked whether or not they thought the talkers were famous. However, many of the participants who were unable to identify at least one talker claimed that they knew that the talkers were famous, but they were simply unable to identify the talkers. 6 One-tailed tests are reported for tests with an a priori prediction about the direction of an effect (e.g., faster RTs in the match than in the control condition). Also, Cohen’s d was calculated for within- and betweenparticipants data using an online effect size calculator. Cognitive Flexibility Laboratory (June 18, 2008). Retrieved from http://www. cognitiveflexibility.org/effectsize/ on October 14, 2011.
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Table 2 Reaction time (RT) results in milliseconds Experiment
Match
Mismatch
Control
Match Priming*
Mismatch Priming**
1: Famous 2: Nonfamous
879 922
903 933
908 966
−29 −44
−5 −33
*Match RT minus control RT **Mismatch RT minus control RT
revealed a significant effect of priming for the match, but not the mismatch, condition (see Table 2). RTs in the match condition were significantly shorter than RTs in the control condition, t(40) = 2.75, p = .004, Cohen’s d = 0.44, but RTs in the mismatch and control conditions were equivalent, t < 1.0. An additional planned comparison demonstrated that RTs in the match condition were significantly shorter than RTs in the mismatch condition, t(40) = 1.75, p = .044, Cohen’s d = 0.29.
Discussion Unlike previous research using a speeded-shadowing task (McLennan & Luce, 2005), we found that matching primes were more effective than mismatching primes. There was a long-term repetition priming effect only when the same talker repeated the words. Previous work using a speededshadowing task, which encourages relatively fast processing, found no talker effects. Consequently, these data appear to be inconsistent with the time-course hypothesis (however, we revisit this issue in the General Discussion section), as well as previous results supporting this hypothesis (Mattys & Liss, 2008; McLennan & González, 2012; McLennan & Luce, 2005; Vitevitch & Donoso, 2011), or at least indicate that the time-course hypothesis may be limited to perceiving words spoken by unknown talkers. Unlike in previous studies, words in the present study were extracted from sentence context, rather than being recorded in isolation. Consequently, we conducted Experiment 2 in order to examine whether we obtained talker effects due to our use of famous talkers or to the use of words extracted from sentences.
Experiment 2: Nonfamous talkers Method Participants Thirty-nine participants, different from those in Experiment 1 but meeting the same criteria, participated.
Materials Two nonfamous talkers (one male, one female) recorded the same words in the same sentences as the famous talkers from Experiment 1, and the stimuli were extracted from these sentences. The 24 experimental words had a mean duration of 423 ms (SD = 89 ms). As with the famous talkers, the durations of the stimuli produced by the male (389 ms, SD = 81 ms) were significantly shorter than the durations of the stimuli produced by the female (456 ms, SD = 86 ms), t(46) = 2.78, p = .008. As in Experiment 1, on average, the experimental stimuli were accurately identified by more than 9 out of the 10 different screening participants. Design and procedure The design and procedure were identical to those in Experiment 1.
Results One participant was excluded from the analysis for having a mean RT greater than three standard deviations above the grand mean. RTs were excluded on the basis of the same criteria as those in Experiment 1, resulting in the exclusion of 14 RTs (1.6%). Mean PC was 95%. We performed a 3 (prime: match, mismatch, control) ×2 (talker during the target block: male, female) repeated measures ANOVA on the RTs to correct responses. The prime × talker interaction did not reach significance, F (2, 74) = 2.97, p = .06, η p2 = .074. The marginally significant effect was driven by a somewhat stronger priming effect for the female talker than for the male talker during the target block. We observed a main effect of talker, F (1, 37) = 7.81, p = .008, η p2 = .17, indicating faster RTs to the male talker than to the female talker, presumably due to the duration difference. We observed a main effect of prime, F (2, 74) = 6.20, p = .003, η p2 = .14. Planned comparisons consisting of paired one-tailed t -tests revealed a significant effect of priming in both the match and mismatch conditions. RTs in the match and mismatch conditions were both significantly shorter than RTs in the control condition,
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t (37) = 3.29, p = .001, Cohen’s d = 0.57, and t (37) = 2.58, p = .007, Cohen’s d = 0.50, respectively. An additional planned comparison demonstrated that RTs in the match and mismatch conditions were equivalent, t < 1.0.
Discussion Unlike in Experiment 1, but consistent with previous findings in support of the time-course hypothesis, there was a longterm repetition priming effect both when words were repeated by the same talker and when the talker changed. Priming in the same- and different-talker conditions was equivalent. Consequently, we are able to rule out the use of stimuli extracted from sentence context as the locus of the talker effects in Experiment 1.7
Combined analyses The key difference between Experiments 1 and 2 was whether or not words in the mismatch condition served as effective primes. In Experiment 2, but not Experiment 1, RTs in the mismatch condition were significantly shorter than RTs in the control condition. Consequently, using an independent onetailed t-test we directly compared the RT difference between the mismatch and control conditions in Experiments 1 and 2. This difference was larger in Experiment 2 than in Experiment 1, t(77) = 1.65, p = .051, Cohen’s d = 0.37. Given the use of the speeded-shadowing task, the results demonstrate that the time-course hypothesis may be limited to the perception of words spoken by unknown talkers. However, an independent two-tailed t-test revealed significantly longer durations for the stimuli in Experiment 1 (mean = 505 ms) than for those in Experiment 2 (mean = 423 ms), t(94) = 4.09, p < .001, Cohen’s d = 0.84. Consequently, if participants were simply responding more slowly in Experiment 1, which would not be surprising given the longer stimulus durations, then perhaps the results of Experiments 1 and 2 are consistent with the time-course hypothesis after all. Nevertheless, participants were actually responding more quickly in Experiment 1 (mean RT = 897 ms) than in Experiment 2 (929 ms). Although this difference was not significant, t(77) = 1.18, p = .12, Cohen’s d = 0.27, there was 7
Nevertheless, besides being produced by famous and nonfamous talkers, there are at least two other differences between the stimuli used in Experiments 1 and 2. First, the stimuli in Experiment 1 came from prepared speeches, while the stimuli in Experiment 2 came from read speech. Second, the stimuli in Experiment 1 came from professional speakers, while the stimuli in Experiment 2 came from nonprofessional speakers. On the basis of the results of the present study alone, we cannot completely rule out one or both of these other differences as modulating (or contributing to) the presence and absence of talker effects.
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a trend in the opposite direction of greater than 30 ms. Considering the longer stimulus durations produced by the famous talkers, the fact that participants were not responding more slowly in Experiment 1 allows us to be confident that our results were not due to slower processing in Experiment 1 than in Experiment 2. If anything, participants were responding more quickly in Experiment 1, consistent with the evidence mentioned previously in which words produced by familiar talkers are recognized more quickly.
General discussion The purpose of the present study was to test whether the timecourse hypothesis was limited to perceiving words produced by unknown talkers. We now have evidence that, indeed, the time-course hypothesis appears to be limited to unknown talkers. Using a speeded-shadowing task, we found evidence that talker-specific representations were affecting the perception of spoken words relatively early with famous (Experiment 1), but not with nonfamous (Experiment 2), talkers. Furthermore, given that participants were not responding more slowly to the famous talkers (indeed, there was a trend in the opposite direction), these results challenge the time-course hypothesis. Prior to this study, researchers had found talker effects when processing was slowed due to the use of a hard lexical decision (McLennan & Luce, 2005; Vitevitch & Donoso, 2011) or a delayed-shadowing (McLennan & Luce, 2005) task or the use of dysarthric (Mattys & Liss, 2008) or foreign-accented (McLennan & González, 2012) speech. The present results provide evidence that talker-specific representations can affect spoken word recognition relatively early, adding to our understanding of the circumstances under which listeners are likely to access specific representations (McLennan, 2007). A possible alternative account for the present set of results is that the female and male famous talkers are simply less similar to (more different from) one another than the female and male nonfamous talkers. If so, rather than the famous versus nonfamous distinction, perhaps this relative lack of similarity between the famous talkers accounts for the talker effects with famous talkers, and the use of relatively similar nonfamous talkers accounts for the lack of talker effects with nonfamous talkers. In order to examine this possibility, we analyzed the differences in fundamental frequency in the productions of the experimental stimuli between the male and female famous talkers and the male and female nonfamous talkers, as shown in Table 3. However, a two-tailed paired t-test revealed that the mean difference between the nonfamous talkers was actually significantly greater than the mean difference between the famous talkers, t(23) = 2.58, p = .02, Cohen’s d = 0.59. Therefore, we can rule out an account based on greater
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Table 3 Mean fundamental frequency (Hz) values for (and differences between) the male and female talkers’ productions of the experimental stimuli in Experiments 1 and 2 Experiment
Male
Female
Difference
Talker Effects
1: Famous 2: Nonfamous
122 119
185 201
63 82
Yes No
differences between the famous talkers as the locus of the different pattern of talker effects in Experiments 1 and 2. There are at least two possible explanations for the present results. First, according to the framework initially motivating the time-course hypothesis, the reason talker-specific details should come into play relatively late is that they are typically less frequent than underlying abstract (talker-independent) representations. While the talker-specific lexical representations of previous studies may have lacked strength due to participants’ relative inexperience with the talkers used in those studies, it might be the case that as we are repeatedly exposed to an individual talker, the input maps onto relatively stronger talker-specific lexical representations. This frequency-based account would mean that the results are actually consistent with the time-course hypothesis. Nevertheless, while a frequency-based explanation might account for listeners we hear on a daily basis, such an explanation may be less likely for talkers we hear less often, including the famous talkers used in the present study. An attentional-based account provides the second, perhaps more likely, account for the present results. Indeed, recent evidence demonstrates that attention modulates the timecourse of talker specificity effects (Theodore & Blumstein, 2011). Researchers have discussed the role that attention might play in listeners’ perception (e.g., Nygaard, 2003) and acquisition (e.g., Francis & Nusbaum, 2002) of abstract information and more fine-grained acoustic-phonetic structure. Several studies have shown that listeners are able to identify famous talkers explicitly (Spence, Rolings & Jerger, 2002; Van Lancker, Krieman & Emmory, 1985). Furthermore, language spoken by familiar and unfamiliar talkers produces different patterns of cortical activation (Shah et al., 2001), supporting the notion that there are differences in language processing. One potential difference is that listeners might pay greater attention to talkers’ voices (or the talker-specific details associated with the spoken words) when hearing words spoken by famous talkers. In other words, the famous talkers were presumably more salient to the listeners, which, in turn, led to more complete processing and retention of talkerspecific characteristics. Since the locus of this attentional account is saliency to the listeners, the same findings should be obtained whenever the input is salient to the listeners and results in a heightened level of arousal, including when the listeners are hearing nonfamous talkers with whom
they are familiar. Unlike the frequency-based account, the attentional-based account would mean the results are inconsistent with the time-course hypothesis and would suggest that processing time is not the only factor affecting the likelihood that listeners access talker-specific representations during spoken word recognition. Although we have no direct evidence that listeners devoted more attentional resources to the stimuli spoken by the famous talkers, our findings clearly demonstrate greater talker effects for words spoken by famous talkers. Consequently, our findings suggest that other factors—in addition to the time course of processing—may influence the role that talker-specific representations play in listeners’ perception of spoken words. A more detailed model of spoken word recognition that accounts for the combined effects of time, attention, and perhaps other factors is ultimately needed, but developing such an account is beyond the scope of this report. Nevertheless, the present findings should stimulate additional research examining the role that famous talkers may play in language perception (perhaps at stages beyond word recognition) and should prompt further consideration of how listeners’ attention may impact on the underlying theoretical issue of abstract versus episodic representations. Acknowledgments This work represents portions of Alisa Maibauer’s master’s thesis (in particular, the research pertaining to the famous talkers; see Maibauer, 2009). We thank Kimberly Neuendorf and Ernest Park for their feedback on this project as members of Alisa’s thesis committee (C.M. was Chair). Portions of this research were supported by research grant number R03 DC 007316 from the National Institute on Deafness and Other Communication Disorders, National Institutes of Health.
Appendix 1 Stimuli used in Experiments 1 and 2 Experimental Words about because before between careful* closely forward* knowledge morning moving myself* paycheck* people problem process repeat respect response
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senior something statement thousand* today* working Filler Words behind happens middle several making million nature resolve* *Hillary Clinton stimulus extracted from video 2 (see Appendix 2)
Appendix 2 Source of stimuli for Experiment 1 Barack Obama Video Title: President-Elect Obama News Conference Date of speech: Friday, November, 7, 2008 Location: Chicago, Illinois Obtain From C-SPAN Video: http://www.c-spanvideo.org/program/282297-1 Hillary Clinton Video 1 Title: Senator Hillary Clinton at New York Delegation Breakfast in Denver, CO Date of speech: Monday, August 25, 2008 Location: Denver, Colorado Obtain From C-SPAN Video: http://www.c-span.org/Events/Sen-Hillary-Clinton-D-NYat-New-York-Delegation-Breakfast-in-Denver-CO/11053/ Hillary Clinton Video 2 Title: Senator Hillary Clinton Press Conference Date of speech: Wednesday, May, 7, 2008 Location: Shepherdstown, West Virginia Obtain From C-SPAN Video: h t t p : / / w w w. c - s p a n v i d e o . o r g / p r o g r a m / C l i n t o n CampaignNew&showFullAbstract=1
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18 Schacter, D. L., & Church, B. A. (1992). Auditory priming: Implicit and explicit memory for words and voices. Journal of Experimental Psychology: Learning, Memory, & Cognition, 18, 915–930. Shah, N. J., Marshall, J. C., Zafiris, O., Schwab, A., Zilles, K., Markowitsch, H. J., & Fink, G. R (2001). The neural correlated of person familiarity: A functional magnetic resonance imaging study with clinical implications. Brain, 124, 804–815. Spence, M. J., Rolings, P. R., & Jerger, S. (2002). Children’s recognition of cartoon voices. Journal of Speech, Language, and Hearing Research, 45, 214–222. Theodore, R. M. & Blumstein, S. E. (2011). Attention modulates the timecourse of talker-specificity effects in lexical retrieval. Poster
Atten Percept Psychophys (2014) 76:11–18 presented at the 162nd Meeting of the Acoustical Society of America, San Diego, CA. Van Lancker, D. R. (1991). Personal relevance and the human right hemisphere. Brain and Cognition, 17, 64–92. Van Lancker, D., Krieman, J., & Emmory, K. (1985). Familiar voice recognition: Patterns and parameters. Part I: Recognition of backward voices. Journal of Phonetics, 13, 19–38. Van Lancker, D. R., Cummings, J. L., Kreiman, J., & Dobkin, B. H. (1988). Phonagnosia: A dissociation between familiar and unfamiliar voices. Cortex, 24, 195–209. Vitevitch, M. S., & Donoso, A. (2011). Processing of indexical information requires time: Evidence from change deafness. The Quarterly Journal of Experimental Psychology, 64, 1484–1493.
Famous talker effects in spoken word recognition Alisa M. Maibauer & Teresa A. Markis & Jessica Newell & Conor T. McLennan
Published online: 24 December 2013 # Psychonomic Society, Inc. 2013
Abstract Previous work has demonstrated that talkerspecific representations affect spoken word recognition relatively late during processing. However, participants in these studies were listening to unfamiliar talkers. In the present research, we used a long-term repetition-priming paradigm and a speeded-shadowing task and presented listeners with famous talkers. In Experiment 1, half the words were spoken by Barack Obama, and half by Hillary Clinton. Reaction times (RTs) to repeated words were shorter than those to unprimed words only when repeated by the same talker. However, in Experiment 2, using nonfamous talkers, RTs to repeated words were shorter than those to unprimed words both when repeated by the same talker and when repeated by a different talker. Taken together, the results demonstrate that talkerspecific details can affect the perception of spoken words relatively early during processing when words are spoken by famous talkers. Keywords Spoken word recognition . Specificity effects . Variability . Time course . Famous talkers . Attention . Priming . Lexical representation and processing A major issue in various areas of cognitive science is determining the nature of mental representations. This issue has been manifested as debates over general versus specific representations. In the present study, we focused on talker variability and its representational implications for spoken word recognition. T. A. Markis : J. Newell : C. T. McLennan (*) Language Research Laboratory, Department of Psychology, Cleveland State University, 2300 Chester Avenue, Cleveland, OH 44115, USA e-mail: [email protected] A. M. Maibauer Department of Internal Medicine, Virginia Commonwealth University, Richmond, VA, USA
Researchers from psychology, linguistics, and related domains have examined the role that variability in surface information (e.g., change of talkers) plays in listeners’ ability to recognize spoken words, as a way to investigate the nature of the representations in the mental lexicon. The focus in the present study is determining whether talker-independent (abstract) or talker-specific (episodic) lexical representations affect listeners’ perception of words spoken by famous talkers. In order to investigate this issue, we used the long-term repetition-priming paradigm in which stimuli are presented in two blocks, separated by a distractor task. If priming is unaffected by a talker change, such that “people” spoken by Talker A is primed equally well by Talker A or Talker B, then an abstract representation is presumably accessed. If, however, priming is attenuated by a talker change (a talker effect), such that “people” spoken by Talker A is only (or more) primed by Talker A, then an episodic representation is presumably accessed. Previous long-term repetition-priming research has shown that talker changes can affect processing under certain conditions (Schacter & Church, 1992). The overwhelming majority of previous studies have been conducted with unknown talkers (Bradlow, Nygaard & Pisoni, 1999; Goldinger, Pisoni & Logan, 1991; Martin, Mullennix, Pisoni & Summers, 1989; Mullennix, Pisoni & Martin, 1989). While these studies have undoubtedly advanced our understanding of representational and processing issues in spoken language, we still know relatively little about the nature of representations for words produced by familiar talkers. There is evidence that language produced by familiar talkers is stored and processed differently than language produced by unknown talkers. In particular, the right hemisphere may play a special role for familiar voices (and familiar faces, names, etc.; Van Lancker, 1991). Furthermore, there is evidence that listeners are faster to shadow words produced by familiar talkers than those produced by unfamiliar talkers (Nygaard, Sidaras & Alexander, 2008).
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According to abstractionist theories, talker information is discarded through a normalization process (Pisoni, 1997), and lexical representations are void of talker-specific details (McClelland & Elman, 1986). According to episodic theories, multiple traces are stored, which include our experience hearing the same word produced by different talkers (Goldinger, 1997). While both theoretical approaches are able to account for some of the results, a clearer picture emerges when the theories are integrated into a hybrid account (Goldinger, 2007). Consequently, rather than debating between abstract and episodic representations, the emphasis is now on determining the circumstances under which each type of representation is more or less likely to affect listeners’ perception of spoken words (McLennan, 2007). At least two such circumstances have been identified. First, there is evidence that episodic (talker-specific) information is located in the right hemisphere and abstract (talkerindependent) information is stored in the left hemisphere (González & McLennan, 2007; Marsolek & Burgund, 2008; Van Lancker, 1991; Van Lancker, Cummings, Kreiman & Dobkin, 1988). Second, there is evidence that lack of (or attenuated) priming for words repeated by a different talker is more likely when processing is relatively slow. According to the time-course hypothesis, abstract information affects processing early, and prior to any effects of talker-specific representations (Luce & Lyons, 1998; McLennan & Luce, 2005). Although there is mounting evidence in support of this time-course hypothesis (Mattys & Liss, 2008; McLennan & González, 2012; McLennan & Luce, 2005; Vitevitch & Donoso, 2011), all of these studies used stimuli produced by talkers that were unknown to the participants. We conducted two experiments to test whether the predictions of the time-course hypothesis are limited to perceiving words produced by unknown talkers. To do so, we investigated potential differences in talker effects, depending on whether the words were spoken by famous (Experiment 1) or nonfamous (Experiment 2) talkers. In both experiments, in order to encourage relatively fast processing, we used the speeded-shadowing task, in which participants are instructed to shadow (or repeat) a spoken word as quickly and accurately as possible. Previous work with nonfamous talkers found no talker effects using the speeded-shadowing task, when processing was relatively fast, and found that talker effects emerged when a delayed-shadowing task was used (McLennan & Luce, 2005). Because words are recognized more quickly when produced by familiar talkers (Nygaard et al., 2008; Nygaard, Sommers & Pisoni, 1994), no talker effects should emerge. More specifically, assuming that the time-course hypothesis generalizes to famous talkers, then in both Experiments 1 and 2, responses to repeated words would be expected to be faster than responses to unprimed words, both when repeated by the same talker and when repeated by a different talker, and there
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should be no difference between the same- and different-talker conditions (i.e., no talker effects). However, if the predictions of the time-course hypothesis are indeed limited to perceiving words spoken by unknown talkers, then perhaps talker effects will emerge with famous talkers, despite relatively fast processing. More specifically, in Experiment 1 (with famous talkers), but not in Experiment 2 (with nonfamous talkers), responses to repeated words would be expected to be faster than responses to unprimed words only when repeated by the same talker, and responses in the same-talker condition should be faster than responses in the different-talker condition (i.e., talker effects in Experiment 1, but not in Experiment 2). The familiar talker stimuli used in previous research are almost always unknown to the participants before the experiment. Participants undergo a familiarization process where they learn to identify the talkers that appear later during the experiment. In the present research, we investigated the processing of words spoken by talkers already familiar to the participants prior to the study. The present study (1) extends time-course predictions to the perception of words spoken by famous talkers, (2) adds to our understanding of the role that talker variability plays in listeners’ perception of spoken words and, thereby (3) contributes to the important theoretical issue of representational specificity, and (4) is the first to investigate possible differences in specificity for words spoken by famous and nonfamous talkers.1
Experiment 1: Famous talkers Method Participants Forty-two participants recruited from the Cleveland State University community participated. Participants received either participation credit toward a class requirement or extra credit. Participants were right-handed, native speakers of American English, with no reported history of speech or hearing disorders. Materials The stimuli consisted of 24 bisyllabic experimental words and 8 bisyllabic filler words (Appendix 1), all of which were spoken by Barack Obama (BO) and Hillary Clinton (HC). Stimulus words were extracted from CSPAN press conference videos (Appendix 2) using RealPlayer v.11. The audio was extracted with FFmpeg, an open-source multimedia converter. Final stimuli were prepared, and mean amplitudes were 1 The majority of past research involving famous talkers has focused on participants’ abilities to recognize and name famous voices.
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equated, using PeakPro audio editing software. The 24 experimental words had a mean frequency of 313.1 (Kučera & Francis, 1967), and a mean duration of 505 ms (SD = 108 ms). The durations of the stimuli produced by BO (466 ms; SD = 81 ms) were significantly shorter than the durations of the stimuli produced by HC (544 ms; SD = 118 ms), t(46) = 2.65, p = .01. The experimental stimuli underwent an initial screening test to ensure that participants were able to accurately perceive these words extracted from sentence contexts. On average, the stimuli were accurately identified by more than 9 out of the 10 screening participants.
13 Table 1 Experimental conditions and examples Condition Match BO prime→BO target HC prime→HC target Mismatch BO prime→HC target HC prime→BO target Control Unrelated prime→BO target Unrelated prime→HC target
Prime
Target
people BO people HC
people BO people HC
people BO people HC
people HC people BO
(one of the filler words)BO people BO (one of the filler words)HC people HC
Design 2
Two blocks (prime and target) of stimuli were presented. Stimuli for these blocks consisted of the words spoken by BO and HC. Participants were not told the identities of the talkers in advance, or even that they would be hearing famous talkers.3 In both blocks, half the stimuli were spoken by BO, and half by HC. As is illustrated in Table 1, the three types of prime–target pairings were (1) match (same word, same talker), (2) mismatch (same word, different talkers), and (3) control (the word was replaced by an unrelated filler word and did not appear in the prime block). Each of the two blocks consisted of 24 stimuli, eight words in each of the three conditions. The stimuli were counterbalanced such that every word appeared in every condition, and no participant heard a word more than once within a block. Procedure Participants were tested individually in a quiet room and were not told at the beginning of the experiment that there would be two blocks. Participants performed a speeded-shadowing task in which they were instructed to repeat each word as quickly and accurately as possible. After the participants responded, the next trial began. All words were presented binaurally over a headset with SuperLab 4.0.7b software (Cedrus Corporation, 2006) for Mac OSX. To familiarize the participants with the task, 10 practice trials were presented. Participants’ reaction times (RTs), measured from stimulus onset, were recorded with a microphone placed approximately 2
The design and procedure followed Experiment 3A of McLennan and Luce’s (2005) study. 3 Presumably, the magnitude of the effect would be larger if participants were given this information in advance. However, we specifically sought to investigate talker effects with famous talkers without explicitly drawing participants’ attention to the talkers. Furthermore, participants were given a postshadowing questionnaire in which, after being informed of the identities of the talkers, they were asked to indicate their political affiliation, level of interest in politics, and other such information (all of which is reported in Maibauer, 2009). There were no significant relationships of interest between the responses on the questionnaire and the magnitude of the obtained talker effects.
1 in. from their lips that was attached to a SuperLab SV-1 voicekey. To verify accuracy, participants’ responses were recorded with Praat software (Boersma, 2001). Participants were given a math test filler task for approximately 5 min between the prime and target blocks.
Results One participant was excluded due to having a priming effect value (match RT minus control RT) that fell two standard deviations beyond the grand priming effect mean. RTs were excluded if they were less than 200 ms or greater than 2,000 ms,4 resulting in the exclusion of 26 RTs (2%). Mean percentage correct (PC) was 99%.5 We performed a 3 (prime: match, mismatch, control)×2 (talker during the target block: BO, HC) repeated measures ANOVA on the RTs to correct responses. The prime×talker interaction was not significant, F (2, 80) < 1.0, p = .88, η p2 = .003. We observed a main effect of talker, F(1, 40) = 27.13, p < .001, η p2 = .40, indicating faster RTs to BO than to HC, presumably due to the duration difference. We observed a main effect of prime, F (2, 80) = 3.30, p = .04, η p2 = .08. Planned comparisons consisting of paired one-tailed t-tests6 4
RT exclusionary criteria in the speeded-shadowing task followed McLennan and Luce’s (2005) exclusionary criteria. 5 Eighteen (43%) of the participants were able to identify at least one of the famous talkers (HC, n = 13; BO, n = 18). Regardless of whether or not participants were able to identify the talkers, it is highly probable that all participants had been exposed to these particular talkers before the experiment and were aware that they were hearing famous voices. Unfortunately, participants were not asked whether or not they thought the talkers were famous. However, many of the participants who were unable to identify at least one talker claimed that they knew that the talkers were famous, but they were simply unable to identify the talkers. 6 One-tailed tests are reported for tests with an a priori prediction about the direction of an effect (e.g., faster RTs in the match than in the control condition). Also, Cohen’s d was calculated for within- and betweenparticipants data using an online effect size calculator. Cognitive Flexibility Laboratory (June 18, 2008). Retrieved from http://www. cognitiveflexibility.org/effectsize/ on October 14, 2011.
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Table 2 Reaction time (RT) results in milliseconds Experiment
Match
Mismatch
Control
Match Priming*
Mismatch Priming**
1: Famous 2: Nonfamous
879 922
903 933
908 966
−29 −44
−5 −33
*Match RT minus control RT **Mismatch RT minus control RT
revealed a significant effect of priming for the match, but not the mismatch, condition (see Table 2). RTs in the match condition were significantly shorter than RTs in the control condition, t(40) = 2.75, p = .004, Cohen’s d = 0.44, but RTs in the mismatch and control conditions were equivalent, t < 1.0. An additional planned comparison demonstrated that RTs in the match condition were significantly shorter than RTs in the mismatch condition, t(40) = 1.75, p = .044, Cohen’s d = 0.29.
Discussion Unlike previous research using a speeded-shadowing task (McLennan & Luce, 2005), we found that matching primes were more effective than mismatching primes. There was a long-term repetition priming effect only when the same talker repeated the words. Previous work using a speededshadowing task, which encourages relatively fast processing, found no talker effects. Consequently, these data appear to be inconsistent with the time-course hypothesis (however, we revisit this issue in the General Discussion section), as well as previous results supporting this hypothesis (Mattys & Liss, 2008; McLennan & González, 2012; McLennan & Luce, 2005; Vitevitch & Donoso, 2011), or at least indicate that the time-course hypothesis may be limited to perceiving words spoken by unknown talkers. Unlike in previous studies, words in the present study were extracted from sentence context, rather than being recorded in isolation. Consequently, we conducted Experiment 2 in order to examine whether we obtained talker effects due to our use of famous talkers or to the use of words extracted from sentences.
Experiment 2: Nonfamous talkers Method Participants Thirty-nine participants, different from those in Experiment 1 but meeting the same criteria, participated.
Materials Two nonfamous talkers (one male, one female) recorded the same words in the same sentences as the famous talkers from Experiment 1, and the stimuli were extracted from these sentences. The 24 experimental words had a mean duration of 423 ms (SD = 89 ms). As with the famous talkers, the durations of the stimuli produced by the male (389 ms, SD = 81 ms) were significantly shorter than the durations of the stimuli produced by the female (456 ms, SD = 86 ms), t(46) = 2.78, p = .008. As in Experiment 1, on average, the experimental stimuli were accurately identified by more than 9 out of the 10 different screening participants. Design and procedure The design and procedure were identical to those in Experiment 1.
Results One participant was excluded from the analysis for having a mean RT greater than three standard deviations above the grand mean. RTs were excluded on the basis of the same criteria as those in Experiment 1, resulting in the exclusion of 14 RTs (1.6%). Mean PC was 95%. We performed a 3 (prime: match, mismatch, control) ×2 (talker during the target block: male, female) repeated measures ANOVA on the RTs to correct responses. The prime × talker interaction did not reach significance, F (2, 74) = 2.97, p = .06, η p2 = .074. The marginally significant effect was driven by a somewhat stronger priming effect for the female talker than for the male talker during the target block. We observed a main effect of talker, F (1, 37) = 7.81, p = .008, η p2 = .17, indicating faster RTs to the male talker than to the female talker, presumably due to the duration difference. We observed a main effect of prime, F (2, 74) = 6.20, p = .003, η p2 = .14. Planned comparisons consisting of paired one-tailed t -tests revealed a significant effect of priming in both the match and mismatch conditions. RTs in the match and mismatch conditions were both significantly shorter than RTs in the control condition,
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t (37) = 3.29, p = .001, Cohen’s d = 0.57, and t (37) = 2.58, p = .007, Cohen’s d = 0.50, respectively. An additional planned comparison demonstrated that RTs in the match and mismatch conditions were equivalent, t < 1.0.
Discussion Unlike in Experiment 1, but consistent with previous findings in support of the time-course hypothesis, there was a longterm repetition priming effect both when words were repeated by the same talker and when the talker changed. Priming in the same- and different-talker conditions was equivalent. Consequently, we are able to rule out the use of stimuli extracted from sentence context as the locus of the talker effects in Experiment 1.7
Combined analyses The key difference between Experiments 1 and 2 was whether or not words in the mismatch condition served as effective primes. In Experiment 2, but not Experiment 1, RTs in the mismatch condition were significantly shorter than RTs in the control condition. Consequently, using an independent onetailed t-test we directly compared the RT difference between the mismatch and control conditions in Experiments 1 and 2. This difference was larger in Experiment 2 than in Experiment 1, t(77) = 1.65, p = .051, Cohen’s d = 0.37. Given the use of the speeded-shadowing task, the results demonstrate that the time-course hypothesis may be limited to the perception of words spoken by unknown talkers. However, an independent two-tailed t-test revealed significantly longer durations for the stimuli in Experiment 1 (mean = 505 ms) than for those in Experiment 2 (mean = 423 ms), t(94) = 4.09, p < .001, Cohen’s d = 0.84. Consequently, if participants were simply responding more slowly in Experiment 1, which would not be surprising given the longer stimulus durations, then perhaps the results of Experiments 1 and 2 are consistent with the time-course hypothesis after all. Nevertheless, participants were actually responding more quickly in Experiment 1 (mean RT = 897 ms) than in Experiment 2 (929 ms). Although this difference was not significant, t(77) = 1.18, p = .12, Cohen’s d = 0.27, there was 7
Nevertheless, besides being produced by famous and nonfamous talkers, there are at least two other differences between the stimuli used in Experiments 1 and 2. First, the stimuli in Experiment 1 came from prepared speeches, while the stimuli in Experiment 2 came from read speech. Second, the stimuli in Experiment 1 came from professional speakers, while the stimuli in Experiment 2 came from nonprofessional speakers. On the basis of the results of the present study alone, we cannot completely rule out one or both of these other differences as modulating (or contributing to) the presence and absence of talker effects.
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a trend in the opposite direction of greater than 30 ms. Considering the longer stimulus durations produced by the famous talkers, the fact that participants were not responding more slowly in Experiment 1 allows us to be confident that our results were not due to slower processing in Experiment 1 than in Experiment 2. If anything, participants were responding more quickly in Experiment 1, consistent with the evidence mentioned previously in which words produced by familiar talkers are recognized more quickly.
General discussion The purpose of the present study was to test whether the timecourse hypothesis was limited to perceiving words produced by unknown talkers. We now have evidence that, indeed, the time-course hypothesis appears to be limited to unknown talkers. Using a speeded-shadowing task, we found evidence that talker-specific representations were affecting the perception of spoken words relatively early with famous (Experiment 1), but not with nonfamous (Experiment 2), talkers. Furthermore, given that participants were not responding more slowly to the famous talkers (indeed, there was a trend in the opposite direction), these results challenge the time-course hypothesis. Prior to this study, researchers had found talker effects when processing was slowed due to the use of a hard lexical decision (McLennan & Luce, 2005; Vitevitch & Donoso, 2011) or a delayed-shadowing (McLennan & Luce, 2005) task or the use of dysarthric (Mattys & Liss, 2008) or foreign-accented (McLennan & González, 2012) speech. The present results provide evidence that talker-specific representations can affect spoken word recognition relatively early, adding to our understanding of the circumstances under which listeners are likely to access specific representations (McLennan, 2007). A possible alternative account for the present set of results is that the female and male famous talkers are simply less similar to (more different from) one another than the female and male nonfamous talkers. If so, rather than the famous versus nonfamous distinction, perhaps this relative lack of similarity between the famous talkers accounts for the talker effects with famous talkers, and the use of relatively similar nonfamous talkers accounts for the lack of talker effects with nonfamous talkers. In order to examine this possibility, we analyzed the differences in fundamental frequency in the productions of the experimental stimuli between the male and female famous talkers and the male and female nonfamous talkers, as shown in Table 3. However, a two-tailed paired t-test revealed that the mean difference between the nonfamous talkers was actually significantly greater than the mean difference between the famous talkers, t(23) = 2.58, p = .02, Cohen’s d = 0.59. Therefore, we can rule out an account based on greater
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Table 3 Mean fundamental frequency (Hz) values for (and differences between) the male and female talkers’ productions of the experimental stimuli in Experiments 1 and 2 Experiment
Male
Female
Difference
Talker Effects
1: Famous 2: Nonfamous
122 119
185 201
63 82
Yes No
differences between the famous talkers as the locus of the different pattern of talker effects in Experiments 1 and 2. There are at least two possible explanations for the present results. First, according to the framework initially motivating the time-course hypothesis, the reason talker-specific details should come into play relatively late is that they are typically less frequent than underlying abstract (talker-independent) representations. While the talker-specific lexical representations of previous studies may have lacked strength due to participants’ relative inexperience with the talkers used in those studies, it might be the case that as we are repeatedly exposed to an individual talker, the input maps onto relatively stronger talker-specific lexical representations. This frequency-based account would mean that the results are actually consistent with the time-course hypothesis. Nevertheless, while a frequency-based explanation might account for listeners we hear on a daily basis, such an explanation may be less likely for talkers we hear less often, including the famous talkers used in the present study. An attentional-based account provides the second, perhaps more likely, account for the present results. Indeed, recent evidence demonstrates that attention modulates the timecourse of talker specificity effects (Theodore & Blumstein, 2011). Researchers have discussed the role that attention might play in listeners’ perception (e.g., Nygaard, 2003) and acquisition (e.g., Francis & Nusbaum, 2002) of abstract information and more fine-grained acoustic-phonetic structure. Several studies have shown that listeners are able to identify famous talkers explicitly (Spence, Rolings & Jerger, 2002; Van Lancker, Krieman & Emmory, 1985). Furthermore, language spoken by familiar and unfamiliar talkers produces different patterns of cortical activation (Shah et al., 2001), supporting the notion that there are differences in language processing. One potential difference is that listeners might pay greater attention to talkers’ voices (or the talker-specific details associated with the spoken words) when hearing words spoken by famous talkers. In other words, the famous talkers were presumably more salient to the listeners, which, in turn, led to more complete processing and retention of talkerspecific characteristics. Since the locus of this attentional account is saliency to the listeners, the same findings should be obtained whenever the input is salient to the listeners and results in a heightened level of arousal, including when the listeners are hearing nonfamous talkers with whom
they are familiar. Unlike the frequency-based account, the attentional-based account would mean the results are inconsistent with the time-course hypothesis and would suggest that processing time is not the only factor affecting the likelihood that listeners access talker-specific representations during spoken word recognition. Although we have no direct evidence that listeners devoted more attentional resources to the stimuli spoken by the famous talkers, our findings clearly demonstrate greater talker effects for words spoken by famous talkers. Consequently, our findings suggest that other factors—in addition to the time course of processing—may influence the role that talker-specific representations play in listeners’ perception of spoken words. A more detailed model of spoken word recognition that accounts for the combined effects of time, attention, and perhaps other factors is ultimately needed, but developing such an account is beyond the scope of this report. Nevertheless, the present findings should stimulate additional research examining the role that famous talkers may play in language perception (perhaps at stages beyond word recognition) and should prompt further consideration of how listeners’ attention may impact on the underlying theoretical issue of abstract versus episodic representations. Acknowledgments This work represents portions of Alisa Maibauer’s master’s thesis (in particular, the research pertaining to the famous talkers; see Maibauer, 2009). We thank Kimberly Neuendorf and Ernest Park for their feedback on this project as members of Alisa’s thesis committee (C.M. was Chair). Portions of this research were supported by research grant number R03 DC 007316 from the National Institute on Deafness and Other Communication Disorders, National Institutes of Health.
Appendix 1 Stimuli used in Experiments 1 and 2 Experimental Words about because before between careful* closely forward* knowledge morning moving myself* paycheck* people problem process repeat respect response
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senior something statement thousand* today* working Filler Words behind happens middle several making million nature resolve* *Hillary Clinton stimulus extracted from video 2 (see Appendix 2)
Appendix 2 Source of stimuli for Experiment 1 Barack Obama Video Title: President-Elect Obama News Conference Date of speech: Friday, November, 7, 2008 Location: Chicago, Illinois Obtain From C-SPAN Video: http://www.c-spanvideo.org/program/282297-1 Hillary Clinton Video 1 Title: Senator Hillary Clinton at New York Delegation Breakfast in Denver, CO Date of speech: Monday, August 25, 2008 Location: Denver, Colorado Obtain From C-SPAN Video: http://www.c-span.org/Events/Sen-Hillary-Clinton-D-NYat-New-York-Delegation-Breakfast-in-Denver-CO/11053/ Hillary Clinton Video 2 Title: Senator Hillary Clinton Press Conference Date of speech: Wednesday, May, 7, 2008 Location: Shepherdstown, West Virginia Obtain From C-SPAN Video: h t t p : / / w w w. c - s p a n v i d e o . o r g / p r o g r a m / C l i n t o n CampaignNew&showFullAbstract=1
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