Abstract
Differences between the interaural phase of a noise and a target tone improve detection thresholds. The maximum masking release is obtained for detecting an antiphasic tone (Sπ) in diotic noise (N0). It has been shown in several studies that this benefit gradually declines as an interaural time delay (ITD) is applied to the noise. This decline has been attributed to the reduced interaural coherence of the noise. Here, we report detection thresholds for a 500 Hz tone in masking noise with ITDs up to 8 ms and bandwidths from 25 to 1000 Hz. Reducing the noise bandwidth from 100 to 50 and 25 Hz increased the masking release for 8-ms ITD, as expected for increasing temporal coherence with decreasing bandwidth. For bandwidths of 100–1000 Hz no significant difference in masking release was observed. Detection thresholds with these wider-band noises had an ITD dependence that is fully described by the temporal coherence imposed by the typical monaurally determined auditory-filter bandwidth. A binaural model based on interaural phase-difference fluctuations accounts for the data without using delay lines.
Highlights
The human binaural system can exploit differences between the interaural phase of a masker noise and a target tone to improve detection thresholds [1]
The noise interaural time difference (ITD) directly translates into an interaural phase difference (IPD)
Two of the less-sensitive listeners were further tested in a sensitivity-optimized threshold ITD task, as in [28]
Summary
The human binaural system can exploit differences between the interaural phase of a masker noise and a target tone to improve detection thresholds [1]. If an interaural time difference (ITD) is applied to the noise the Sp detection thresholds increase. If the ITD is exactly half of the tone period, it is as antiphasic as the tone around the tone frequency, and the binaural benefit is diminished [2]. This can be avoided by applying the ITD to both tone and noise [3] or by looking at ITDs that are an integer multiple of the tone period, as discussed in [2]. The second aspect is that the binaural benefit gradually declines with increasing ITD even if the first periodic issue is avoided. Two different mechanisms have been proposed to account for the latter gradual decline, which is in the focus of the present study
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