| Research Abstract |
Inter-sensory integration has been investigated especially in terms of the nature-nurture problem. The present study examined developmental changes in auditory-visual integration in speech perception including the McGurk effect. The McGurk effect is an audiovisual illusion showing that hearing speech is influenced by conflicting visual lip-read information.
The subjects Were 3-year-old, 7-year-old, 11-year-old, and 20-year-old native speakers of Japanese. Each age group included 10 subjects. Stimuli were created from/ba/and/da/spoken by a Japanese female talker. Videotaped syllables were edited, resulting in audiovisually conflicting stimuli (audio/ba/, video/da/, and vice versa) as well as audiovisually matching stimuli (audio/ba/, video/ba/). In addition to original intact stimuli, degraded stimuli were prepared. The degraded auditory stimuli were created by lowpass filtering with a cut-off frequency of 730 kHz, the degraded visual stimuli were obtained by mosaic effect at and around
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the mouth. Based on pilot experiments, the level of the degradation was set so that accuracy of the unimodal performance was about 80% in the 20-year-old. There were several modality conditions : A-only (clear and lowpass), V-only (clear and mosaic), and AV (combinations of the unimodal conditions). The task of the subjects were to report what they perceived by choosing either/ba/or/da/.
In the-A- and V-only conditions, clear stimuli were perceived very accurately, showing no age differences. In the AV conditions, the size of the McGurk effect was the same across the age groups when the auditory component was clear. When the auditory component was degraded, the size of the McGurk effect was significantly smaller in the 3-year-old than in the other age groups, although the 3-year-old showed as strong a McGurk effect as the other age groups.
These results suggest that the integration for audiovisually conflicting stimuli emerges relatively late, whereas audiovisually matching stimuli are perceptually integrated at a very early stage of life. Less
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