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Abstract:
Abstract: We have previously shown, using fMRI, that hearing
people activate auditory cortex bilaterally (BA 22, 42/ 41) when
speechreading lipspoken numbers (Calvert et al., 1997; MacSweeney
et al., submitted). We have argued that this cross-sensory
activation results from the development of crossmodal neuronal
connections established early in life through exposure to
coincident auditory and visual speech. Although speechreading is
often their primary means of access to spoken language,
congenitally profoundly deaf people are not exposed to the auditory
component of speech. Such individuals provide an opportunity to
test the hypothesis that auditory cortex is intrinsically involved
in silent speechreading. In an fMRI study contrasting hearing and
congenitally deaf subjects, we found that activation of auditory
cortex was severely attenuated in the deaf group, all of whom were
excellent speechreaders. This contrasts with the extensive
activation of these areas in a woman who became deaf at the age of
30 months. These data suggest that early auditory experience
influences the extent to which lateral temporal networks are
recruited during the development of the perception of visual
speech.
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