Dissociation between lexical and indexical processing during speech perception
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1
Rice University, Department of Psychology, United States
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2
Villanova University, Department of Psychology, United States
The speech stream includes both lexical and indexical information. The former contains information about the words being spoken and the latter contains information about the social context of the speech (e.g., gender, age or geographical origin of the speaker)—listeners must also use this information to accurately recognize speech by factoring out this contextual variability. Theories differ with respect to how these two types of information are processed during the course of spoken word recognition. Abstractionist theories argue that the ability to recognize words relies on segmental representations that abstract away from indexical information. Exemplar theories argue that speech recognition depends on matching the speech stream against stored representations of previously heard words that contain both lexical and indexical information.
For the current project, we compare these two broad theories of speech perception by investigating a single case (MM) of an individual with pure word deafness who has previously been reported in the literature (Slevc et al., 2011). Based on previous studies, it is clear that MM has difficulties processing lexical information in spoken words. Despite intact spoken and written production and intact reading, MM is unable to repeat spoken words, match spoken words to pictures, or discriminate consonants or vowels that differ by a single feature. His audiology exam showed normal hearing, and he was unimpaired at processing the meaning of non-linguistic acoustic stimuli (e.g. matching a “moo” sound to a picture of a cow).
We investigated whether MM was impaired at processing both lexical and indexical information from the speech stream, using a standard speech categorization paradigm, like those found in the categorical perception literature. Two continua were developed. To test for processing of lexical information, we used a nine step voice-onset time continuum between the words beach and peach. To test for processing of indexical information, we used a nine step talker gender continuum (manipulating f0 and formant frequencies) that varied between being perceived as a male voice to being perceived as a female voice. MM and 10 control participants were presented with 10 instances of each of the 9 steps along either continue, and asked to make categorical judgements (beach vs. peach or male vs. female). As shown in Figure 1, control participants show typical categorization functions for both the lexical and indexical continua. As expected, MM was at chance for the beach-peach continuum. In contrast, he was no different than the control participants for the male-female continuum.
Based on this pattern, we conclude that MM has a selective impairment in processing lexical information from the speech stream, without a corresponding impairment in processing indexical information, specifically talker gender. This dissociation is predicted by abstractionist theories of speech perception, but difficult to reconcile with exemplar theories.
References
Slevc, L. R., Martin, R. C., Hamilton, A. C., & Joanisse, M. F. (2011). Speech perception, rapid temporal processing, and the left hemisphere: a case study of unilateral pure word deafness. Neuropsychologia, 49(2), 216-230.
Keywords:
Speech Perception,
categorical perception,
Pure word deafness,
exemplar theory,
abstractionist theories
Conference:
Academy of Aphasia 55th Annual Meeting , Baltimore, United States, 5 Nov - 7 Nov, 2017.
Presentation Type:
poster or oral
Topic:
General Submission
Citation:
Fischer-Baum
S and
Toscano
J
(2019). Dissociation between lexical and indexical processing during speech perception.
Conference Abstract:
Academy of Aphasia 55th Annual Meeting .
doi: 10.3389/conf.fnhum.2017.223.00116
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Received:
02 May 2017;
Published Online:
25 Jan 2019.
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Correspondence:
Dr. Simon Fischer-Baum, Rice University, Department of Psychology, Houston, Texas, 77005, United States, simon.j.fischer-baum@rice.edu