John F. Olsen
Lab. Neurophysiol., NIMH, NIH, Bldg. 110, P.O. Box 608, Poolesville, MD 20837
In this study neural sensitivity to rate of rise was measured. The
responses of 32 medial geniculate neurons to linear increments of a broadband
noise from a defined baseline level were recorded extracellularly. Step rise
time (3--96 ms), step amplitude (6--24 dB), and baseline level (0--73 dB SPL)
were varied independently. A typical response to the step consisted of a
transient burst of 1--8 spikes. Response probability increased as a function of
the step's rate of rise (amplitude/rise time), such that increases in rise time
could be traded for proportional increases in step amplitude to obtain a
criterion response. Increases in baseline level decreased the slope of the
probability versus rate of rise function and increased the threshold rate of
rise. Response probability was independent of peak level (=baseline level+step
amplitude). The results show that the response of a common type of medial
geniculate neuron is determined by the rate at which stimulus amplitude
increases from a defined background level, indicating a possible role for these
neurons in the perceptual segregation of auditory events [A. S. Bregman, P. A.
Ahad, and J. Kim,