Integration of monaural and binaural evidence of vowel formants

The intelligibility of speech is sustained at lower signal-to-noise ratios when the speech has a different interaural configuration from the noise. Th is paper argues that the advantage arises in part because listeners combine evidence of the spectrum of speech in the across-frequency profile of inte raural decorrelation with evidence in the across-frequency profile of inten sity. To support the argument, three experiments examined the ability of li steners to integrate and segregate evidence of vowel formants in these two profiles. In experiment 1, listeners achieved accurate identification of th e members of a smalt set of vowels whose first formant was defined by a pea k in one profile and whose second formant was defined by a peak in the othe r profile. This result demonstrates that integration is possible. Experimen t 2 demonstrated that integration is not mandatory, insofar as listeners co uld report the identity of a vowel defined entirely in one profile despite the presence of a competing vowel in the other profile. The presence of the competing vowel reduced accuracy of identification, however, showing that segregation was incomplete. Experiment 3 demonstrated that: segregation of the binaural vowel, in particular, can be increased by the introduction of an onset asynchrony between the competing vowels. The results of experiment s 2 and 3 show that the intrinsic cues for segregation of the profiles are relatively weak. Overall, the results are compatible with the argument that listeners can integrate evidence of spectral peaks from the two profiles. (C) 2000 Acoustical Society of America. [S0001-4966(00)02206-2].