Estimates of Ripple-Density Resolution Based on the Discrimination From Rippled and Nonrippled Reference Signals

Abstract

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.

Cognitive factors contribute to speech perception in cochlear-implant users and age-matched normal-hearing listeners under vocoded conditions

“…The ripple-discrimination task involved spectrally rippled stimuli with a fixed peak-to-valley ratio of 30 dB, while the ripple rate was varied adaptively to track the highest ripple rate or density, in ripples per octave (rpo), at which a phase reversal of the ripples is detectable. This threshold is thought to provide a measure of the limits of spectral resolution, and does not appear to suffer from the potential confounds of temporal-envelope cues, which can affect spectral-ripple detection at high ripple rates (Anderson et al , 2012; Nechaev et al , 2019). The ripple-detection task involved measuring the minimum detectable peak-to-valley ratio at a fixed ripple rate of 0.25, 0.5, 1, or 2 rpo.…”

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

“…Given the finding that combination products do not determine the ripple-density resolution, there is a more realistic hypothesis that explains the task-dependent difference in resolutions by different degrees of involvement of the excitation-pattern and temporal-processing mechanisms of frequency analysis, as has been suggested previously (Anderson et al, 2012;Milekhina et al, 2019;Nechaev et al, 2019).…”

“…Such discrimination was possible at very high ripple densities: up to 60 ripples/oct by Anderson et al. (2012) , 26.1 ripples/oct by Nechaev et al. (2019) , and 34.2 ripples/oct by Milekhina et al.…”

Ripple density resolution dependence on ripple width

“…It has been argued [11,13,14] that for different discrimination tasks, different mechanisms dominate. For distinguishing between two rippled signals that have different ripple positions…”

“…When the resolution was assessed by distinguishing two rippled stimuli with equal ripple densities but different ripple phases, the resolution was less than 10 ripples/oct [6,7]. When the resolution was assessed by distinguishing between a rippled stimulus and a non-rippled stimulus, it was several times higher: nearly 60 ripples/oct [11], 26 ripples/oct [13], or more than 34 ripples/oct [14]. However, the influence of the ripple width on the ripple density resolution was not investigated in these studies.…”