Responses of auditory-nerve fibers to characteristic-frequency tones and low-frequency suppressors

Responses of single auditory-nerve fibers to combinations of low-frequency (suppressor) and characteristic frequency (CF) tones were recorded. The shapes of period histograms were observed as the level of the suppressor was raised. For fibers with CFs above 5.0 kHz, at the lowest suppressor levels used, the phase of the suppressor tone which caused instantaneous rate to increase when presented alone caused a rate decrease when added to a CF tone. For suppressor frequencies of 500 and 100 Hz, as suppressor level is increased, two peaks appear in the period histograms. Further increase in level causes first one, then the other of these peaks to disappear and the histogram takes on the shape of the histogram to the suppressor alone. A similar progression of histogram shape follows a decrease in CF tone level for fixed suppressor level.