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Abstract:
Keele and Ivry (1991) considered the cerebellum an 'internal
clock' supporting temporal computations both in the motor and in
the perceptual domain. Since durational parameters contribute to
the recognition of some consonants, cerebellar dysfunctions must be
expected to impair speech perception. Accordingly, a previous study
(Ackermann et al. 1997) found bilateral cerebellar disorders to
compromise identification of two lexical items ("Boten", /bo:tn/,
'messengers' versus "Boden", /bo:dn/, 'floor') exclusively
differing in a durational measure, i.e., intersyllabic silent
period (occlusion time). By contrast, recognition of other,
non-durational acoustic cues was unimpaired. In order to
investigate the contribution of the cerebellum to the processing of
durational parameters of speech utterances, a fMRI study was
performed using the minimal pair cognates "Boten / Boden" as test
materials (12 subjects; 1.5 T Siemens Vision, 600 trials, 28 slices
EPI, voxel size 3x3x3 mm, TE = 55 ms). Two series of items were
applied randomized: (a) a sequence of "Boten / Boden" utterances
exclusively differing in occlusion time; (b) a sequence of "Boten /
Boden" utterances differing in a non-durational parameter
(word-medial aspiration noise). Identification of the durational
minimal pair cognates yielded significantly higher activation of
both cerebellar hemispheres. In addition, a significant hemodynamic
response of Broca's area could be detected. These data indicate
that a distributed network of cortical and subcortical structures
outside the temporal lobe might be recruited during speech
perception.
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