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Abstract:
Previous work provided evidence for a short, finite (~30-40
ms) temporal window of integration in the formation of the auditory
M100, during which stimulus duration is encoded in the accumulation
processes underlying the M100 and provides a primary modulating
force in M100 amplitude. Here we investigate temporal resolution of
the M100 component by measuring evoked responses to tones
containing brief gaps of silence. Gaps of varying durations (2, 5,
7, 10, 15, 20, 30, 50 ms) were inserted at a point +10 ms post
onset in 1 kHz tones of 250 ms duration. Tones were presented
binaurally and evoked responses were simultaneously sampled from
both hemispheres using a twin 37-channel biomagnetometer
(MAGNES-IITM, BTi, San Diego, CA) in 7 healthy adults. We report
two general effects: i) M100 latency prolongation as a function of
gap duration, even with the gap of shortest duration (2 ms). This
effect was more pronounced in the left hemisphere. And ii) M100
amplitude varied in a linear fashion, with lower amplitudes found
for tones with longer gaps. This result is related to previous
findings where stimulus on-time or duration provided a key
modulating force in M100 amplitude: in the present case, M100
amplitude was modulated as a function of stimulus on-time in spite
of a discontinuity - or temporal gap - within the stimulus.
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