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Abstract:
This neurolinguistic study investigated prefrontal cortex
activation in speech discrimination tasks by comparing stimuli that
do or do not require overt segmentation of phonemes. In the first
experiment, subjects were asked to determine whether the first
sound of word pairs (e.g., "dip-tip") was the same or different. In
the second experiment, subjects were asked to make the same
judgment on pairs in which the rime of the syllable differed (e.g.,
"dip-ten"). Speech conditions in both experiments were compared to
a tone discrimination control condition. Six native speakers of
English were presented with the speech and tone conditions in each
experiment. Behavioral data showed that subjects were highly
accurate in both experiments. Cross-correlation thresholding was
used to analyze the fMRI data. Two analyses were performed on the
data, one in which the images were transformed into standard
stereotactic space to determine common areas of activation across
subjects and the second in which regions of interests were analyzed
for each of the subjects. The results of both experiments showed
left superior temporal activation. However, only the second
experiment revealed evidence of activity in the left prefrontal
cortex. These results suggest that prefrontal areas are not
involved in the perceptual analysis of the speech input itself, but
rather are involved when task demands require segmentation.
Supported by NIH DC R01-3378-01 and DC00314.
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