STIMULUS-ONSET DOMINANCE IN THE PERCEPTION OF BINAURAL INFORMATION

With dichotic signals presented by headphone, stimulus-onset dominance (the 'precedence effect') was investigated for various types of binaural-processing-based percepts. The following three dichotic cues were considered: (1) inter-aural time delay (IATD, underlying the lateralization of the sound image), (2) inter-aural level difference (IALD, also underlying lateralization), and (3) inter-aural cross correlation (IACC, underlying the spaciousness of the sound image in terms of broadness/ compactness). For all three cases, the degree of stimulus-onset dominance is estimated by one and the same experimental paradigm, which is essentially the same as used by Aoki and Houtgast [Hear. Res. 59, 25-30 (1992)1: When subdividing a brief stimulus in two parts of equal duration, a leading and a trailing part, in which the dichotic cue has opposite values, the over-all sensation is found to be dominated by the cue in the leading part. This dominance can be compensated by shortening the leading part (while keeping total signal duration constant), providing a quantitative measure for the onset dominance. The signals were octave-band filtered noise (center frequencies 500 or 2000 Hz) or 7-kHz low-pass filtered noise, and total signal duration was 5, 10, 20 or 40 ms. The results obtained for the four signal durations have been converted to a weighting function, representing the perceptual weight of the dichotic information as a function of time-after-signal-onset. These estimated weighting functions (derived separately for IATD, IALD and IACC, and for each of the three types noise signals) show a peak during the first few milliseconds, followed by a brief period of reduced weight (5 to 10 ms after signal onset), recovering after, roughly, 20 ms. This typical peak-dip-shaped weighting function is most clear for IATD and IALD (lateralization), and is a little less pronounced for IACC (broadness/ compactness).