Lateralization thresholds obtained under conditions in which the precedence effect is assumed to operate

Interaural differences of time (IDT) thresholds were measured with 600-microseconds transients. The initial experiment was a successful replication of previous experiments that have obtained the precedence effect in lateralization paradigms (e.g., Yost and Soderquist, 1984). When a dichotic click followed a diotic click with an interclick interval (ICI) less than 1 ms or larger than 5 ms, IDT thresholds were generally less than 40 microseconds. For ICIs between 1 to 5 ms, IDT thresholds increased to approximately 220 microseconds. Poorest performance was observed for ICIs of 1.75 to 2.35 ms. During the course of conducting a series of planned experiments on this effect, a substantial drop in IDT thresholds was observed across the ICIs of maximum interest (1 to 5 ms). The precedence effect, which we had replicated in our initial experiment, essentially "disappeared" when the subjects were given sufficient practice on the lateralization task. A number of conditions were explored in an unsuccessful attempt to recover the precedence effect in these experienced subjects. The implications of these results are discussed.