Effects of modulator shape at thresholds and supra-thresholds spectral modulation perception

Abstract

Spectral modulation detection is common method to assess spectral envelope perception in research and clinical settings. Prior investigations into spectral modulation (SM) detection have used two different modulator shapes: a sinusoidal envelope on a logarithmic amplitude scale or a sinusoidal envelope on a linear amplitude scale. The former creates a sinusoidally shaped excitation pattern, while the latter creates an excitation pattern with broad peaks and sharp valleys. What impact, if any, modulator shape has on SM perception at detection threshold or at supra-threshold levels is unknown. To investigate potential perceptual differences between waveform shapes: (1) SM detection was measured for modulation frequencies ranging from 0.5 to 8.0 cycles/octave; (2) Spectral modulation masking was measured for SM frequencies of 0.5 and 2.0 cycles/octave. The SM phase of the masker was manipulated (0, 90, or 180 degrees) so that maskers had a peak, a midpoint, or a valley at 1147 Hz. Tone detection (1147 Hz) was measured for the logarithmic and linear sinusoidal SM envelope shapes for each of the three phases. Results revealed significant differences between the two spectral envelope shapes for both spectral modulation detection and for spectral modulation masking. [Work supported by NIH R01DC015051].