Psychophysical estimates of cochlear phase response: masking by harmonic complexes

Area of Science:

• Auditory Neuroscience
• Psychoacoustics
• Signal Processing

Background:

• Harmonic complexes with identical frequency and amplitude but varying phase spectra can differ in masking effectiveness.
• Positive Schroeder-phase waveforms are generally less effective maskers than negative Schroeder-phase waveforms, despite similar envelopes and power spectra.
• Masking differences are hypothesized to arise from interactions between masker phase and the basilar membrane's phase characteristics.

Purpose of the Study:

• To investigate the relationship between masker phase spectrum and auditory masking.
• To explore how varying the phase gradient of harmonic complexes affects masking.
• To model these psychoacoustic findings using auditory filter simulations.

Main Methods:

• Systematically altered the Schroeder-phase algorithm to vary the gradient of stimulus phase change across masker bandwidth.
• Employed a detection task where observers identified a signal tone added in-phase to a masker component.
• Tested maskers with frequencies ranging from 200 to 5000 Hz and a fundamental frequency of 100 Hz.

Main Results:

• Masking differences of 5-10 dB were observed for phase gradients changing by 10% for signal frequencies between 1000-4000 Hz.
• The optimal phase gradient for minimal masking varied with signal frequency: low frequencies were least masked by rapidly changing phases, high frequencies by shallow gradients.
• A gammachirp filter qualitatively predicted changes in the phase-by-frequency function curvature but did not fully capture all empirical data quantitatively.

Conclusions:

• The phase spectrum of a masker, specifically its phase gradient, plays a crucial role in auditory masking.
• Auditory processing exhibits frequency-dependent sensitivity to phase gradients.
• While the gammachirp filter shows promise, further refinement is needed for accurate modeling of phase-gradient-dependent masking.