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Abstract:
To elucidate the neural mechanisms involved in early auditory
perception we recorded subjects' EEG in response to auditory click
trains. Click train stimulus onset asynchrony (SOA) varied between
1 and 1000 ms.. In a previous study we showed that the gamma band
response (GBR) elicited by clicks is a transient response which
closely mirrors perception. Here we extend our study to include the
slow wave response (SWR) comprised of frequency components < 13
Hz. Specifically, we characterize the dynamics of the SWR by
filtering the broadband response into narrow, overlapping bands and
comparing the peak amplitudes in each band to click train SOA. The
resulting spectral maps show a differential enhancement of the low
frequency components relative to the high frequency components for
SOAs less than 25 ms.. This differential enhancement diminishes
with increasing filter frequency up to gamma band frequencies where
the pattern subsides. Thus, while the GBR amplitude shows no
dependence on click train SOA, SWR amplitudes are strongly
correlated. Given previous evidence that established a correlation
between N100 latency and the spectral composition of acoustic
signals, we propose that the SWR reflects a cortical integration
process in which individual (click) responses are summed with an
effective time constant that corresponds to the psychophysical
order threshold.
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