SOME ASPECTS OF THE LATERALIZATION OF ECHOED SOUND IN MAN - I - THE CLASSICAL INTERAURAL-DELAY BASED PRECEDENCE EFFECT

The precedence effect in two-click stimuli was investigated by measuri ng observers' sensitivity to interaural time delays (ITDs) as a functi on of interclick interval (ICI). A two-interval two-alternative forced -choice discrimination paradigm was used in two stimulus configuration s: type I, a dichotic click with a given ITD preceded a diotic click; and type II, a dichotic click followed a diotic click. Threshold ITDs were measured in each configuration for a finely sampled distribution of ICIs that ranged from 0.1 to 25.6 ms. Performance was characterized by the ''threshold elevation factor'' (TEF) which normalized each of the observers' type I and type II ITD thresholds relative to their ITD threshold for a single dichotic click. The finer sampling of ICIs rev ealed two novel results: First, for two observers, sensitivity to ITD in the later arriving ITD (type II) oscillated in a consistent and sys tematic way with changes in ICI. Second, when the ICI reached 12.8 ms, ITD thresholds in the type I and type II configurations were equal bu t nearly a factor of 2 greater than for a single dichotic click. Some aspects of the data are consistent with the phenomenon of binaural ada ptation. (C) 1998 Acoustical Society of America. [S0001-4966(98)03911- X].