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Abstract:
Research using ERP and MEG techniques has demonstrated that
auditory processes habituate to repeated stimuli and rapidly
dishabituate to stimulus changes at the acoustic, phonemic, and
lexical levels. This event-related fMRI study explores the
feasibility of using dishabituation paradigms to investigate the
functional organization of speech perception. In event-related
runs, subjects passively listened to a stream of identical auditory
word stimuli presented once every 800 ms, interrupted every 16-24
secs by an "oddball" auditory word. In blocked localizer runs,
subjects alternately listened to 30 sec. mixtures of random
auditory words or the attenuated background noise. A 1.5 T scanner
acquired 20 axial slices every 3.2 sec. A comparison of the
auditory word vs. background noise condition in the localizer runs
was used to to identify significant (p < .005) regions of
interest in the superior temporal gyrus. These regions were applied
to the 5 images aquired after each oddball event. As expected,
signal levels consistently increased 0-6 sec following an oddball
stimulus, and then returned to baseline habituated levels. Our
results demonstrate a successful application of a habituation
paradigm using event-related fMRI and a manipulation at the lexical
level. Future extensions of this approach will investigate the
relationship between different levels of representation and
regional patterns of cortical dishabituation.
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