Effects of categorical speech perception during active discrimination of stop-consonants and vowels within the left superior temporal cortex
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1
Kyoto University, Human Brain Research Center, Graduate School of Medicine, Japan
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2
Kyoto University, Department of Psychology, Graduate School of Letters, Japan
In this experiment we aimed at investigating the categorical perception of consonants and vowels, and we aimed at elucidating which cortical areas reflect the categorical representation of phonemes using human magnetoencephalography (MEG). To this end, we designed stimuli along a phonological continuum from /ba/ to /da/, /bo/ to /do/, /ba/ to /bo/, and /da/ to /do/, thus entailing changes of the voiced stop-consonant or the steady-state vowel of a CV syllable. In a psychophysical experiment, we first determined the category boundaries for each individual participant. Then, in an MEG experiment, we presented participants with consecutive pairs of either same or different CV syllables. In case of a pair of different stimuli, the two stimuli were either from within a category or they crossed a category-boundary. During the MEG experiment, the participants actively discriminated the stimulus pairs.
Behaviorally, we found that discrimination was easier for the between- compared to the within-category contrast for both consonants and vowels. However, this categorical effect was significantly stronger for the consonants compared to vowels, in line with a more continuous representation of vowels. At the neural level, we observed significant repetition suppression of MEG evoked fields, i.e., lower amplitudes for physically same compared to different stimulus pairs, from around 430 to 500 ms after onset of the second stimulus. Source reconstruction revealed generating sources of this repetition suppression effect within left middle to posterior superior temporal sulcus/gyrus. A region-of-interest analysis within this region showed a clear categorical effect for consonants, but not for vowels.
Thus, our study corroborates the proposition that categorical effects are stronger for consonants compared to vowels. Furthermore, it provides further evidence for the important role of left superior temporal areas in categorical representation during active phoneme discrimination.
Keywords:
Magnetoencephalography,
categorical perception,
spoken language,
phoneme perception,
healthy human participants
Conference:
XII International Conference on Cognitive Neuroscience (ICON-XII), Brisbane, Queensland, Australia, 27 Jul - 31 Jul, 2014.
Presentation Type:
Poster
Topic:
Sensation and Perception
Citation:
Altmann
C,
Uesaki
M,
Ono
K,
Matsuhashi
M,
Mima
T and
Fukuyama
H
(2015). Effects of categorical speech perception during active discrimination of stop-consonants and vowels within the left superior temporal cortex.
Conference Abstract:
XII International Conference on Cognitive Neuroscience (ICON-XII).
doi: 10.3389/conf.fnhum.2015.217.00039
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Received:
19 Feb 2015;
Published Online:
24 Apr 2015.
*
Correspondence:
Dr. Christian Altmann, Kyoto University, Human Brain Research Center, Graduate School of Medicine, Kyoto, Japan, chfaltmann@gmail.com