Temporal (Phase and Time) Disparities in Lateralization

The topic of this paper concerns the judgement of just noticeable differences (JND) and of complete lateral position for dichotic 1 000-Hz stimuli with phase or onset time or delay differences and for a click. The 1 000-Hz sinusoids had 30 ms steady state with 10 or 50 ms rise/decay time and were presented at 50 dB HL in listeners with normal hearing. For every value of Δ, Δonset or delay, the presentation consisted of blocks of 20 trials and the JND was determined as the phase or onset time or delay differences producing 80% of correct responses (forced choice). The intracranial 1 000-Hz tone image with long disparities was evaluated for 90, 180 and 270° Δ, for 250, 500 and 750 μs Δonset and for 250, 500 and 750 μs delay. Our results demonstrate that the interaural time differences with suitable headphone onset cues have a negligible effect on JND in pure-tone lateralization tests; the JND for a 1 000-Hz tone is based on phase cues only. With 180 and 270° phase shifts, the interaural onset time differences, with 10 ms rise-fall time, become critical and override phase information. The JND for clicks on the contrary is based on time cue only. The intracranial click image with long disparities and duality threshold was evaluated.