The effects of randomizing interaural phases of components spectrally distant from the target on detection of a dichotic pitch.

Abstract

The present study examined the ability of subjects to detect an interaural phase delay of a 20-Hz-wide section of wideband noise. The narrow-band target was centered on 500 Hz and generated a dichotic, Huggins-type pitch. Thresholds for interaural phase delay detection were measured as a function of the width of the surrounding diotic noise, which was also centered on 500 Hz. Interaural phases for frequency components outside of the diotic band were drawn randomly from a rectangular distribution. The spectrum of the entire stimulus ranged from 1–1500 Hz. A two-down, one-up tracking procedure was used to estimate interaural delay thresholds, in which each trial consisted of two 500-ms noise bursts, separated by 250 ms of silence. The two intervals were identical except that the interaural delay of the 20-Hz wide target band was introduced after 250 ms in the target interval. Thresholds were obtained for diotic bandwidths of 900, 700, 500, 300, 200, 150, 125, and 100 Hz. Thresholds decreased systematically as the bandwidth of the diotic surrounding noise was increased from 100 to 500 Hz, and were unchanged as the diotic band was further widened. Comparisons were made with conditions in which the noise outside the diotic band was removed instead of being presented with random interaural phases.