Forward masking of the compound action potential: Thresholds for the detection of the N1 peak

Abstract

A computerized two-interval forced-choice method was used to measure the threshold for detection of the N1 peak of the compound action potential (CAP) recorded at the round window of the chinchilla in response to a 23-ms probe tone. A 100-ms, pure-tone masker of equal frequency preceded the probe tone. Threshold shifts produced by the masker were measured as the intensity of the masker and the time delay between the masker and the probe were varied. The techniques differ from prior studies in that forward masking of the compound action potential has been quantified as shifts in detection thresholds rather than decrements in the magnitude of the N1 peak. Results were compared to analogous measures for single neurons in the auditory nerve [E. M. Relkin and D. G. Pelli, J. Acoust. Soc. Am. 82, 1679–1691 (1987)] and analogous psychophysical measures of forward masking. Preliminary findings indicate that forward masking of the CAP more closely corresponds to that observed psychophysically than does the forward masking observed in the response of a single neuron. [Work supported by the Deafness Research Foundation and NIH.]