Masking patterns for simple spectral stimuli

Abstract

Auditory processing appears to consist of a series of domain-specific filtering operations that separate complex stimuli into different auditory channels. This begins with tuning in the audio-frequency domain, followed by tuning in the temporal frequency (modulation) domain, and perhaps tuning in the spectral frequency domain. To explore the hypothesis that envelope channels tuned to spectral frequency exist in the auditory system, a masking experiment was designed to measure masking patterns in the spectral domain. Noise carriers with flat spectra were either 1 (800–1600 Hz, 6400–12<th>800 Hz) or 6 octaves wide (200–12<th>800 Hz) and were shaped with sinusoidal spectral envelopes (in cycles per octave). Masker frequencies were 1, 3, or 5 cyc/oct with a spectral contrast of 20 dB. Masked contrast thresholds were measured for signal frequencies ranging from 1.5 octaves below to 2 octaves above the masker frequency. The resulting masking patterns revealed maximum masking at the masker frequency and a gradual decrease in the masking above and below the masker frequency. This tuning is consistent with the assumption of spectral envelope channels tuned to different spectral frequencies. Secondary peaks obtained in several masking patterns may suggest inhibitory interactions among separate spectral channels. [Work supported by NIH NIDCD RO1DC04403.]