Level dependence in behavioral measurements of auditory-filter phase characteristics

Two masking experiments were conducted to behaviorally estimate auditory-filter phase curvatures at different stimulus levels. Maskers were harmonic complexes consisting of equal-amplitude tones and phase spectra with varied curvatures. In Experiment 1, sinusoidal signal thresholds were measured at 2 and 4 kHz at fixed masker levels ranging from 50 to 90 dB sound pressure level (SPL). In Experiment 2, the masker level that just masked a sinusoidal signal at 2 and 4 kHz was measured at fixed signal levels of 25, 38, and 50 dB SPL. For both experiments, the estimated phase curvature approached zero (became less negative) with increasing stimulus level. This shift could suggest that the off-frequency phase characteristic of the auditory filter has an increasingly greater role on the estimated auditory-filter phase curvature at higher stimulus levels. This explanation is supported through the use of psychophysical modeling.