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Abstract:
Previous research has shown that in comparison to adults,
children have similar latency and larger amplitude MMNs in response
to synthetic speech stimuli (Kraus, et al., 1993). However, a
recent investigation using natural vowel stimuli found smaller and
later MMNs in children, and differential affects of attention as
well, when compared to adults (Morr, et.al, 1999, 2000). In the
current study, we used natural re-sythesized speech stimuli to
elicit electrophysiological and behavioral responses for normal
adults and children. In the active condition, subjects were asked
to detect an infrequently presented target tone among the deviant
and standard consonant syllables. In the passive task, subjects
ignored the stimuli and attended to a silent video or read a book.
Formant frequencies were edited along a continuum to create
prototypical and non-prototypical variants of /ba/ and /da/. The
adults and children displayed very similar behavioral performances
for discrimination and identification. Differences were observed in
the electrophysiological results; a larger MMN was found in adults
during the attend task compared to the passive task. Children
displayed no clear negativity in the typical latency range of MMN,
although a large, late negativity was observed. Attention to the
task was not sufficient to elicit an MMN in children. These results
suggest maturational differences in brain discrimination processes
related to stimulus properties.
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