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 measuring observers' sensitivity to interaural time delays (ITDs) as a function of interclick interval (ICI). A two-interval two-alternative forced-choice discrimination paradigm was used in two stimulus configurations: 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 revealed two novel results: First, for two observers, sensitivity to ITD in the later arriving ITD (type II) oscillated in a consistent and systematic 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 but nearly a factor of 2 greater than for a single dichotic click. Some aspects of the data are consistent with the phenomenon of binaural adaptation.