Adaptation effects in binaural experiments

Abstract

Experiments were conducted to examine some of the effects of imbalanced interaural parameters on binaural lateralization. We examined adaptation both to stimuli with interaural amplitude differences and to stimuli with interaural time differences. To measure the adaptation over time, 30‐trial runs were made with each run lasting about 15 min. On each trial, the subject was required to adjust the interaural time delay from an initial random value to a value that resulted in a centered image. For a low‐pass filtered pulse train with an interaural amplitude difference of 10 dB, the amount of interaural time delay needed to center the image changed from 250 μs at the outset to 100 μsec at the end of the run. These results are consistent with earlier results using a paradigm nearly identical to ours [M. P. Bertrand, Proc. R. Soc. Med. 65, 3–4 (Sept. 1972)]. For the same low‐pass filtered pulse train with no interaural amplitude differences, but with the initial random delay restricted to one ear, the amount of time delay needed to center the image changed by as much as 50 μs during the course of a run, i.e., at the end of a run the subjects no longer heard a diotic presentation (zero delay) in the center of their heads. Two possible mechanisms of adaptation will be discussed. [Work supported by NIH.]