Rippled spectrum discrimination in noise: Effects of compression

Abstract

In psychophysical experiments, cochlear compression can be derived by the comparison of on- and low-frequency masking, assuming that in the signal representation, the responses to both the signal and on-frequency masker are equally compressed while the response to the low-frequency masker is not compressed. In the present study, this approach was used to assess the influence of compression on the discrimination of complex signal spectra. The signals were rippled noise, 0.38-oct wide, centered at 2 kHz, 40 to 90 dB SPL. The ripple-density discrimination limit was measured using the ripple-phase reversal test. The simultaneous maskers were 0.5-oct wide noise centered either at the signal frequency (on-frequency) or 0.75-oct below the signal (low-frequency). Increase in the masker level resulted in a decrease in the ripple-density resolution limit. The growth of the on-frequency masker was approximately 1:1. The growth of the low-frequency masker revealed no compression at signal levels from 40 to 50 dB, and increasing compression at higher levels, up to 0.28 dB/dB at signal levels from 70 to 90 dB SPL. The observed manifestation of compression implies that rippled-spectrum discrimination is minimally susceptible to lateral suppression and off-frequency listening.