Sinusoidal spectral modulation masking period patterns

Abstract

Knowledge of the internal auditory representation of spectral envelope features is critical to the understanding of auditory perception by listeners with normal and impaired hearing. Previous investigators have used forward and simultaneous masking to derive masking patterns that reveal the influence of lateral suppression and other factors on the internal representation of various spectral envelopes (e.g., narrowband noise and steady-state vowels). The present study followed a general approach, in which the internal representation of spectral shape was estimated on the basis of spectral masking patterns obtained with sinusoidal spectral modulation. Simultaneous- and forward-masked thresholds were measured for probe signals as a function of spectral modulation frequency (cycles/octave), phase, and depth (peak-valley contrast in dB) superimposed on a noise carrier (400–6400 Hz). For relatively low modulation frequencies (<1 cycle/octave), masking patterns closely mimicked features of the external spectrum. For very high modulation frequencies (>2 cycles/octave), masking patterns revealed reduced spectral contrast, consistent with the limited frequency selectivity of the auditory system. For intermediate modulation frequencies (1–2 cycles/octave), considerable spectral sharpening was evident. The three-dimensional space defined by spectral modulation frequency, depth, and internal contrast will be discussed in terms of predicting the internal representation of arbitrary complex spectral envelopes.