Discrimination of rippled-spectrum patterns in noise: A manifestation of compressive nonlinearity

Abstract

In normal-hearing listeners, rippled-spectrum discrimination was psychophysically investigated in both silence and with a simultaneous masker background using the following two paradigms: measuring the ripple density resolution with the phase-reversal test and measuring the ripple-shift threshold with the ripple-shift test. The 0.5-oct wide signal was centered on 2 kHz, the signal levels were 50 and 80 dB SPL, and the masker levels varied from 30 to 100 dB SPL. The baseline ripple density resolutions were 8.7 oct-1 and 8.6 oct-1 for the 50-dB and 80-dB signals, respectively. The baseline ripple shift thresholds were 0.015 oct and 0.018 oct for the 50-dB and 80-dB signals, respectively. The maskers were 0.5-oct noises centered on 2 kHz (on-frequency) or 0.75 to 1.25 oct below the signal (off-frequency maskers). The effects of the maskers were as follows: (i) both on- and low-frequency maskers reduced the ripple density resolution and increased the ripple shift thresholds, (ii) the masker levels at threshold (the ripple density resolution decrease down to 3 oct–1 or ripple shift threshold increased up to 0.1 oct) increased with increasing frequency spacing between the signal and masker, (iii) the masker levels at threshold were higher for the 80-dB signal than for the 50-dB signal, and (iv) the difference between the masker levels at threshold for the 50-dB and 80-dB signals decreased with increasing frequency spacing between the masker and signal. Within the 30-dB (from 50 to 80 dB SPL) signal level, the growth of the masker level at threshold was 27.8 dB for the on-frequency masker and 9 dB for the low-frequency masker. It is assumed that the difference between the on- and low-frequency masking of the rippled-spectrum discrimination reflects the cochlear compressive non-linearity. With this assumption, the compression was 0.3 dB/dB.

High Ripple-Density Resolution for Discriminating Between Rippled and Nonrippled Signals: Effect of Temporal Processing or Combination Products?

“…Such a masker may produce low-frequency masking of the primary signal (the effect of upward spread of masking). Due to the upward spread of masking, low-frequency maskers reduce the ripple-density resolution ( Milekhina et al., 2017 ; Nechaev et al., 2015 ; Supin et al., 2001 , 2003 ). The low-frequency masking of the primary signal must be distinguished from the on-frequency masking of low-frequency combination products.…”

“…This may be done by comparing masking effects in different experimental paradigms. Low-frequency maskers reduce ripple-density resolution at levels exceeding that of the signal ( Milekhina et al., 2017 ). In contrast, masking of low-frequency combination products might occur at lower masker levels because (a) lower levels of combination products than of the primary signal and (b) on-frequency masking of combination products in contrast to off-frequency masking of the primary signal.…”