Tone detection thresholds in interaurally delayed noise of different bandwidths
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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.
Key words: Binaural hearing / Binaural unmasking / Interaural phase difference / Interaural coherence