John F. Culling
MRC Inst. of Hear. Res., University Park, Nottingham NG7 2RD, UK
Common periodicity has been proposed as a basis for segregating concurrent sounds that differ in fundamental frequency. Common interaural time delay may play an analogous role in segregating complex sounds whose sources differ in spatial position. To explore this analogy, masked identification thresholds were measured for synthesized vowels in pink noise in several binaural conditions. The across-frequency coherence of each sound's interaural phase relationships was manipulated. The results were interpreted in terms of an interaural cross-correlation mechanism that groups components that produce cross-correlation maxima at the same delay. Masking release (compared to the condition where both noise and vowel were in phase at each ear) was found to depend mainly upon the coincidence across frequency, at the same correlation delay, of cross-correlation maxima due to the noise. Masking release was largely independent of the pattern of interaural correlations generated by the target vowel, providing the pattern differed from that of the masking noise. The result is analogous to the demonstration that the periodicity of maskers, not target vowels determines ease of segreagation based on differences in fundamental frequency, and shows that the binaural masking release of complex sounds includes an across-frequency grouping mechanism.