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Abstract:
Impairments of phonemic processing are associated with a
variety of neurological conditions ranging from cerebellar and
basal ganglia pathology to left frontal and left posterior
temporal-parietal lobe lesions. In two experiments, groups of
patients with damage to each of these neural areas were tested on
phonemic identification and production tasks to assess cortical and
subcortical contributions to phonemic processing. In Experiment 1,
patients and age-matched controls were asked to identify phonemic
tokens on both a voicing and place of articulation continuum.
Subcortical patients were relatively unimpaired at this task,
although they were less accurate than controls in identifying an
endpoint on the place of articulation continuum. Cortical patients
were not only less accurate at identifying the endpoints of both
continua, they also exhibited little evidence of categorical
perception. For Experiment 2, controls and patients were asked to
produce the syllables /ba/, /pa/, and /da/. Variability of voice
onset time(VOT) production, was greater for subcortical patients
and the duration of their formant transitions were longer than
controls. Cortical patients showed disruptions of duration and
variability for both VOT and formant transition intervals. These
results are in line with the type of motoric or linguistic
computations hypothesized to originate from subcortical and
cortical areas.
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