Lateralization based on interaural phase differences: effects of frequency, amplitude, duration, and shape of rise/decay.

Experiments in lateralization were performed to evaluate the relative contribution of envelope and phase cues in binaural hearing with particular reference to the effects of frequency, amplitude, shape of rise/decay, and duration of peak amplitude. Pure-tone signals were presented with interaural phase shifts ranging between 90 degrees and 360 degrees. For a given value of phase shift, the leading signal was presented randomly to the right or left ear over a block of 100 trials, and the laterality of the resultant image was judged. Rise/decay time was varied from 5 to 200 ms across blocks. The results confirmed our previous finding that a rise/decay time of at least 200 ms is required to secure a psychophysically steady-state signal. This value will, however, depend on the values chosen for the other signal parameters. Within limits, decreasing intensity could be compensated for by decreasing rise/decay, suggesting the psychophysical importance of the initial segment of the signal (precedence effect). For low frequencies of 650 to 1250 Hz, performance is sensitive to interaural phase shift and largely independent of frequency. For higher frequencies of 1500 and 2000 Hz, lateralization is independent of the phase cue and also largely insensitive to change in rise/decay time. Finally, performance remains unchanged with variation in peak duration ranging from 25 to 200 ms.