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.
Highlights
The ability to discriminate spectral patterns is an important characteristic of the auditory system
The baseline ripple density resolution and ripple shift thresholds were measured for signal levels of 50 and 80 dB SPL
The masked ripple density resolution and ripple shift thresholds were measured for signal levels of 50 and 80 dB SPL and masker levels from 30 to 100 dB SPL
Summary
The ability to discriminate spectral patterns (spectral resolution) is an important characteristic of the auditory system. Discrimination of rippled-spectrum patterns in noise tone or narrowband maskers (the tuning curve paradigm; see [1] for a review); two-tone maskers [2,3,4]; narrow-band noise (the critical band paradigm; see [5] for a review); notch-noise [6,7,8]; or rippled noise [4, 9,10,11,12] In these investigations, the basilar membrane was considered a bank of equivalent frequency-tuned auditory filters with certain qualities. Several analytical expressions have been suggested to summarize the data on the equivalent rectangular bandwidth (ERB) of the auditory frequency-tuned filters as a function of the center frequency, e.g., [13] Based on this (or a similar) equation and ignoring possible nonlinear interactions between the frequency-tuned filters, the responses of the basilar membrane to signals with various spectral compositions may be predicted
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