Spectral modulation transfer functions as a function of duration and level

Abstract

Spectral modulation transfer functions (SMTF) were estimated as a function of stimulus duration and level to evaluate the influence of those parameters on spectral shape perception. Listeners discriminated between noise stimuli having either a flat or a sinusoidal spectral shape. Spectral contrast thresholds were determined by adaptively varying the peak-to-valley contrast using a 3-down, 1-up tracking algorithm in a cued, two-interval, forced-choice procedure. Carrier noises had bandwidths of either 6 octaves (200–12<th>800 Hz), or 1 octave (800–1600 Hz, 6400–12<th>800 Hz). Spectral frequencies ranged from 0.25 to 10 cyc/oct and 1.33 to 10 cyc/oct for the 6- and 1-octave conditions, respectively. In Experiment I, the stimulus durations were either 50, 100, 200, 300, or 400 ms. SMTFs were bandpass in shape with best contrast thresholds between 2 and 5 cyc/oct. Decreasing duration had a greater influence on thresholds for low- and high-spectral frequencies than mid-spectral frequencies. In Experiment II, stimulus level was varied in spectral levels from –10 to 50 dB SPL. The shape of the SMTF varied little with level down to No = 10 dB. Decreasing level had a greater influence on low- and high-spectral frequencies than mid-spectral frequencies. [Work supported by NIH NIDCD RO1DC04403.]