Journal of Neuroscience, Vol 5, 3261-3269, Copyright © 1985 by Society for Neuroscience
Representation of tones in noise in the responses of auditory nerve fibers in cats. I. Comparison with detection thresholds
JA Costalupes
Rate and temporal responses evoked by 1-kHz or 8-kHz tones in continuous
broadband noise are described for large populations of auditory nerve
fibers in anesthetized cats. The signal-to-noise ratios (S/Ns) of the tone
and noise stimuli were above behavioral detection thresholds. Stimulus
combinations were presented (1) over a range of moderate to high noise
intensities at a constant S/N and (2) using high intensity noise and
varying S/N. Responses of low (less than 1 spike/sec) and medium (1 to 19
spikes/sec) spontaneous rate (SR) fibers were compared with those of high
SR (greater than 19 spikes/sec) fibers. Low and medium SR fibers with best
frequencies in the region of the test tone frequency exhibited tone-evoked
rate changes at all sound levels tested. High SR fibers, in contrast,
exhibited much weaker tone- evoked rate changes at the lowest noise level
tested. In the presence of high intensity noise, high SR fibers did not
exhibit tone-evoked rate changes due to saturation by the noise. Fibers
with best frequencies in the region of 1 kHz also exhibited strong
phase-locking to the 1 kHz tone which increased as the tone level increased
but which did not differ for the various SR groups. Results suggest that
information in the rate responses of low and medium SR fibers can account
for the encoding of information about tones in noise by the nervous system.