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Abstract:
In terms of the neural basis of speech perception,
left-lateralised (or bilateral) superior temporal gyri have been
identified as candidate processors of the complexity of speech
input, with speech specific processing being a function of left
posterior temporal lobe regions (Wernicke's area). We describe a
different model of the neural basis of speech perception, which
also addresses the existing conflict in the speech perception
literature. Based on several functional neuroimaging studies, we
have identified at least two distinct streams of processing in the
auditory cortex: a left-lateralised system directed lateral and
anterior to primary auditory cortex, involved in the identification
of intelligible speech, and a posteriorly directed stream involved
in the short term representation of speech sounds on the basis of
their sensori-motor representations, i.e. how these sounds would be
repeated. This left-lateralised anterior stream is seen most
clearly when speech stimuli are compared to unintelligible stimuli
of equivalent acoustic structural complexity (Scott et al, 2000).
The posterior route, involving posterior STS, is capable of both
short term storage and gesture-based analysis by synthesis, to both
represent the actions associated with repeating a word or sound,
and to help support speech perception if the input if it is novel,
degraded, or the task is difficult.
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