Three‐tone suppression

Abstract

Responses of single neurons in the anteroventral cochlear nucleus were recorded from anesthetized cats as the intensities of three fixed‐frequency pure tones were systematically varied. One tone, the excitor, was sent to the neuron's CF. Two‐tone suppression of responses to the excitor tone was then studied for a suppressor tone above CF, and then for a suppressor tone below CF. Suppression magnitude was taken as the parallel shift (in dB) of the response‐versus‐intensity function for the excitor tone caused by introducing the suppressor tone at fixed intensities. When all of the two‐tone effects had been studied, three‐tone responses were collected until every relevant intensity combination had been explored in 5‐dB steps. Adding the third tone produced a linear increase in suppression magnitude over either two‐tone condition. The total amount of suppression in the three‐tone case was equal to the sum of the two‐tone suppressive effects. Additivity of suppression was the same for both discharge rate and discharge synchronization. [Work supported by NINCDS grant NS‐14880.]