The Haas effect with and without binaural differences

Abstract

The precedence effect for click signals operates successfully for delays in the range 0.5–5 ms. Previous work in our lab has shown that this effect behaves similarly whether sources are in the azimuthal plane or the horizontal plane. The precedence effect for running speech can operate successfully for delays as long as 50 ms—the ‘‘Haas zone.’’ Experiments were performed to measure two kinds of precedence threshold for running speech, echo threshold (listeners reported a barely perceptible echo), and masked threshold (listeners could barely detect that a lagging sound was present). The results were as follows: (1) Echo threshold levels decreased with increasing delay (20–80 ms) with a slope that was the same whether sources were in the azimuthal plane or the sagittal plane; (2) echo thresholds were higher in the sagittal plane than in the horizontal plane by a constant 3 dB; (3) masked thresholds were systematically 10–15 dB lower than echo thresholds, and there was essentially no difference between azimuthal and sagittal planes. These results support the idea that precedence is functionally similar whether or not binaural differences are present. [Work supported by the NIDCD, DC00181.]