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Abstract:
Adults' cognitive functions rely on specialized neural
networks. In the auditory domain, in particular, different neural
networks within the temporal lobe are involved in the
representation of the different acoustical features of a sound and
also in the phonemic coding of a linguistic stimulus. The goals of
the study were to study whether a cerebral specialization, in
particular for phonemic processing, is present from the early
development. High-density evoked potentials to acoustical and
linguistic changes in series of repeated stimuli were recorded in
4-month-old infants: A change of musical timbre in two tones was
opposed to a change of phoneme, then a voice change to a phoneme
change and at least a change within a phonetic category to a
similar acoustic change that crosses a phonetic boundary. Mismatch
responses to these stimuli exhibit a distinct topography suggesting
that the different features of an auditory stimulus are encoded by
different neural networks in the sensory memory. For example,
dipoles are more dorsal and posterior when a phonetic change is
perceived than when a similar acoustical change without linguistic
signification is processed. Specialized modules are thus present
within the auditory cortex very early in development. There was,
however, no evidence of any greater left hemisphere involvement in
linguistic processing. For both syllables and continuous tones,
higher voltages were recorded over the left hemisphere than over
the right.
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