CATEGORICAL SPEECH-PERCEPTION IN CEREBELLAR DISORDERS

Keele and Ivry (1991) considered the cerebellum an ''internal clock'' responsible for temporal computations both in the motor and in the per ceptual domain. These authors, therefore, expected that the processing of durational parameters of the perceived acoustic speech signal such as voice onset time (VOT) depends upon the cerebellum as well. Howeve r, a preliminary investigation of Ivry and Gopal (1992) revealed unimp aired phoneme-boundary effects in cerebellar patients along a continuu m of monosyllabic stimuli with systematically varied VOT (/ba/-/pa/). Since the energy of the aspiration noise provides additional cues for the discrimination of voiced and voiceless stops, the present study us ed a series of disyllabic stimuli differing in a purely durational par ameter. Both controls and patients with unilateral cerebellar lesion i dentified the endpoints of this continuum in nearly all instances as t he counterparts of a minimal pair (Boten, /bo:tn/, ''messengers'' vers us Boden /bo:dn/, ''floor''). Subjects with bilateral pathology of the cerebellum, in contrast, did not show a comparable phoneme-boundary e ffect. Our data corroborate the hypothesis of the cerebellum as an int ernal clock and implicate a role of this structure in speech perceptio n. (C) 1997 Academic Press.