Interaural spectral asymmetry and sensitivity to interaural time differences

Abstract

Listeners' ability to discriminate interaural time difference (ITD) changes in low-frequency noise was determined as a function of differences in the noise spectra delivered to each ear. An ITD was applied to Gaussian noise, which was bandpass filtered using identical high-pass, but different low-pass cutoff frequencies across ears. Thus, one frequency region was dichotic, and a higher-frequency region monotic. ITD thresholds increased as bandwidth to one ear (i.e., monotic bandwidth) increased, despite the fact that the region of interaural spectral overlap remained constant. Results suggest that listeners can process ITD differences when the spectra at two ears are moderately different.

Figure 1

Schematic depicting the relationship of the noise spectra at the left (top row) and right (bottom row) ears used. The two vertical dashed lines encompass the ISO region, which is the spectral region that is present at both ears. The arrow represents the change to the stimuli that occurred due to the manipulation of interest, and the dotted plot represents the starting point of the manipulation. The low-pass cutoff frequency of the band of noise delivered to the right ear was initially the same as that for the left ear, and was systematically increased in frequency.

Figure 2

(Color online) ITD thresholds, in μs, for the five listeners as a function of the difference in low-pass cutoff frequency (ΔLP) between the two ears, which is expressed in 1∕3 octaves. The left panel depicts data when the base low-pass cutoff frequency was 125 Hz, the right panel shows 250-Hz data (see Table Table 1.).