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Abstract:
Recent clinical and experimental findings indicate
specialization of the left human sylvian cortex for the temporal
processing of verbal and nonverbal auditory stimuli. The present
study used whole-head magnetencephalography (MEG, 143-channels,
sampling rate = 250 Hz) in order to test the hypothesis that the
left supratemporal plane is superior with respect to the detection
of the durational speech parameter voice onset time (VOT). Subjects
(n = 11, age: 24 - 42 years) were sitting during MEG recordings and
instructed to ignore the stimuli (passive oddball design [80%
standard stimuli, 20% deviants], two randomized series of the
syllables /da/ [VOT = 10 msec] and /ta/ [60 msec] in balanced order
across subjects; each block comprising 450 sweeps of a duration of
500 msec). Each stimulus category yielded rather identical
N1m/P2m-complexes at both sides of the brain which neither
significantly differed in latency nor amplitude. In contrast to
/ta/, deviant /da/-syllables showed significant side-differences
with respect to the latency of MMNm (magnetic equivalent to
mismatch negativity). Most presumably, the two stimuli considered,
i.e., events with either short- or long-lag VOT, differ in the
time-course of access to linguistic representations. These findings
indicate that facilitation of acoustic processing at the level of
the supratemporal plane by top-down processes might contribute to
left hemisphere superiority of speech sound processing.
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