Explore the vast range of titles available.

The goal of the study was to investigate how variations in ripple width influence the ripple density resolution. The influence of the ripple width was investigated with two experimental paradigms: (i) discrimination between a rippled test signal and a rippled reference signal with opposite ripple phases and (ii) discrimination between a rippled test signal and a flat reference signal. The ripple density resolution depended on the ripple width: the narrower the width, the higher the resolution. For distinguishing between two rippled signals, the resolution varied from 15.1 ripples/oct at a ripple width of 9% of the ripple frequency spacing to 8.1 ripples/oct at 64%. For distinguishing between a rippled test signal and a non-rippled reference signal, the resolution varied from 85 ripples/oct at a ripple width of 9% to 9.3 ripples/oct at a ripple width of 64%. For distinguishing between two rippled signals, the result can be explained by the increased ripple depth in the excitation pattern due to the widening of the inter-ripple gaps. For distinguishing between a rippled test signal and a non-rippled reference signal, the result can be explained by the increased ratio between the autocorrelated and uncorrelated components of the input signal.

Rippled-spectrum stimuli are used to evaluate the resolution of the spectro-temporal structure of sounds. Measurements of spectrum-pattern resolution imply the discrimination between the test and reference stimuli. Therefore, estimates of rippled-pattern resolution could depend on both the test stimulus and the reference stimulus type. In this study, the ripple-density resolution was measured using combinations of two test stimuli and two reference stimuli. The test stimuli were rippled-spectrum signals with constant phase or rippled-spectrum signals with ripple-phase reversals. The reference stimuli were rippled-spectrum signals with opposite ripple phase to the test or nonrippled signals. The spectra were centered at 2 kHz and had an equivalent rectangular bandwidth of 1 oct and a level of 70 dB sound pressure level. A three-alternative forced-choice procedure was combined with an adaptive procedure. With rippled reference stimuli, the mean ripple-density resolution limits were 8.9 ripples/oct (phase-reversals test stimulus) or 7.7 ripples/oct (constant-phase test stimulus). With nonrippled reference stimuli, the mean resolution limits were 26.1 ripples/oct (phase-reversals test stimulus) or 22.2 ripples/oct (constant-phase test stimulus). Different contributions of excitation-pattern and temporal-processing mechanisms are assumed for measurements with rippled and nonrippled reference stimuli: The excitation-pattern mechanism is more effective for the discrimination of rippled stimuli that differ in their ripple-phase patterns, whereas the temporal-processing mechanism is more effective for the discrimination of rippled and nonrippled stimuli.

The goal of the study was to enlarge knowledge of discrimination of complex sound signals by the auditory system in masking noise. For that, influence of masking noise on detection of shift of rippled spectrum was studied in normal listeners. The signal was a shift of ripple phase within a 0.5-oct wide rippled spectrum centered at 2 kHz. The ripples were frequency-proportional (throughout the band, ripple spacing was a constant proportion of the ripple center frequency). Simultaneous masker was a 0.5-oct noise below-, on-, or above the signal band. Both the low-frequency (center frequency 1 kHz) and on-frequency (the same center frequency as for the signal) maskers increased the thresholds for detecting ripple phase shift. However, the threshold dependence on the masker level was different for these two maskers. For the on-frequency masker, the masking effect primarily depended on the masker/signal ratio: the threshold steeply increased at a ratio of 5 dB, and no shift was detectable at a ratio of 10 dB. For the low-frequency masker, the masking effect primarily depended on the masker level: the threshold increased at a masker level of 80 dB SPL, and no shift was detectable at a masker level of 90 dB (for a signal level of 50 dB) or 100 dB (for a signal level of 80 dB). The high-frequency masker had little effect. The data were successfully simulated using an excitation-pattern model. In this model, the effect of the on-frequency masker appeared to be primarily due to a decrease of ripple depth. The effect of the low-frequency masker appeared due to widening of the auditory filters at high sound levels.

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.

The goal of the study was to investigate the role of combination products in the higher ripple-density resolution estimates obtained by discrimination between a spectrally rippled and a nonrippled noise signal than that obtained by discrimination between two rippled signals. To attain this goal, a noise band was used to mask the frequency band of expected low-frequency combination products. A three-alternative forced-choice procedure with adaptive ripple-density variation was used. The mean background (unmasked) ripple-density resolution was 9.8 ripples/oct for rippled reference signals and 21.8 ripples/oct for nonrippled reference signals. Low-frequency maskers reduced the ripple-density resolution. For masker levels from −10 to 10 dB re. signal, the ripple-density resolution for nonrippled reference signals was approximately twice as high as that for rippled reference signals. At a masker level as high as 20 dB re. signal, the ripple-density resolution decreased in both discrimination tasks. This result leads to the conclusion that low-frequency combination products are not responsible for the task-dependent difference in ripple-density resolution estimates.

The goal of the study was to assess cochlear compression when rippled-spectrum signals are perceived in noise assuming that the noise might produce both masking and confounding effects. In normal listeners, discrimination between rippled signals with and without ripple phase reversals was assessed in background noise. The signals were band-limited (0.5 oct at a − 6-dB level) rippled noise centered at 2 kHz, with a ripple density of 3.5 oct−1. The noise (masker) was band-limited nonrippled noise centered at either 2 kHz (on-frequency masker) or 1 kHz (low-frequency masker). The masker was simultaneously presented with the signals. Masker levels at the discrimination threshold were measured as a function of the signal level using the adaptive (staircase) two-alternative forced-choice procedure. For the on-frequency masker, the searched-for function had a slope of 0.98 dB/dB. For the low-frequency masker, the function had a slope of 1.19 dB/dB within a signal level range of 30 to 40 dB sound pressure level (SPL) and as low as 0.15 dB/dB within a signal level range of 70 to 80 dB SPL. These results were interpreted as indicating compression of responses to both the signal and on-frequency masker and no compression of the effect of the low-frequency masker. In conditions when above-threshold signals are presented in simultaneous noise (the masker), cochlear compression manifests to a substantial degree despite possible confounding effects.