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Abstract:
University of Technology, Finland. In face-to-face
communication both acoustic and visual consequences of the talker's
articulatory gestures influence speech perception. Seeing
incongruent articulatory gestures may even change the auditory
percept phonetically as occurs in the McGurk effect (McGurk and
MacDonald 1976). We studied the neural basis of auditory
modifications caused by visual speech with a 306-channel whole-head
magnetometer by recording neuromagnetic mismatch fields (MMFs),
which are elicited in the auditory cortices by an occasional change
in a sound sequence. We wanted to find out whether an acoustically
identical, but visually and perceptually deviant stimulus could
elicit MMF and compare its cortical source with the source of MMF
elicited by both acoustically and visually deviant audiovisual
utterance. We presented among congruent /ipi/ utterances both
congruent (acoustic /iti/, visual /iti/) and incongruent (acoustic
/ipi/, visual /iti/) deviants, which were both perceived as /iti/.
Preliminary results from 9 subjects show that both congruent and
incongruent deviants elicited MMFs. Thus, even when there was no
acoustical difference between the deviant and standards, MMF was
elicited, in agreement with Sams et al. (1991). In some subjects
MMF elicited by incongruent deviants had a lower amplitude than
that elicited by congruent ones. The sources of both MMFs seem to
be in the auditory cortices. Our results suggest that the phonetic
change caused by visual speech is detected in the auditory
cortices.
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