Brainstem evoked responses to paired-click stimuli: the use of digital response subtraction.

Brainstem evoked responses were obtained to 60-dB nHL clicks and click pairs presented at 27/s. Paired-click intervals ranged from 9.8 to 0.5 ms. 6 normal-hearing young adults served as subjects. Derived responses were obtained by digital response subtraction of single-click from paired-click responses. Wave V was observed to unsubtracted click 2 of the click pair at paired-click intervals down to 4 ms. Wave V of the derived (subtracted) click 2 response was observed for paired-click intervals down to 1 ms. To assess additivity, the click 1 response of the click pair was compared to the single-click response, and the unsubtracted click 2 response was compared to the derived click 2 response. At longer paired-click intervals, wave V latency was greater for click 1 of the click pair than for the single-click response. This latency difference decreases at shorter paired-click intervals and is attributed to adaptation of click 1 by click 2 of the previous pair. Wave V amplitudes for single-click and paired-click click 1 responses were not significantly different at any paired-click interval. The latency and amplitude for unsubtracted click 2 and derived click 2 responses were not significantly different at any paired-click interval. It is concluded that the responses to click 1 and click 2 of the paired clicks are additive, at least at very brief paired-click intervals.