Binaural Interaction of a Click with a Click Pair

Abstract

The binaural interaction between a single click and a click pair was examined. Two clicks with time separations of 0.5, 1, 2, 4, and 8 msec were presented to one ear, and a single click of controllable interaural time was presented to the other. Two polarity patterns (rarefaction-rarefaction vs rarefaction; and rarefaction-condensation vs rarefaction) were used at pattern rates of 2/, 10/, and 50/sec. Four subjects were asked to adjust interaural time to center all discernable sound images. Lateralizations corresponding to temporal alignment with individual clicks in the pair were found for 8-msec and sometimes for 4-msec separation. For these conditions, the subjects were consciously aware of two images. With 1-msec separation of the pair, subjects were aware of only one image, but in repeated adjustments temporally aligned at both clicks. With 2-msec separation, however, no significant lateralizations were made at the time of the second click. Only one image was discernable corresponding to lateralization of the first click. Analog basilar-membrane displacements produced by the stimuli correlate with some details of the results, but do not explain the absence of a second lateralization at the 2-msec pair separation. The neural mechanisms usually invoked to explain a minimum time interval of about 3 msec are also not adequate to explain these results. Possible explanatory mechanisms such as temporal summation and a neural gate are discussed.