Auditory evoked brain stem responses to trains of stimuli in human adults.

Abstract

This study describes the effect of train length, interstimulus interval, intertrain interval (ITI), and stimulus duration on the transition from the unadapted to the adapted wave V auditory evoked brain stem response (ABR). ABRs were recorded to stimuli presented at two different rates: a slow rate characterizing the unadapted response and a fast rate characterizing the adapted response. Trains of stimuli (a sequence of stimuli separated by intervals of silence) also were presented. Different stimulus parameters defining the trains were varied. Given a sufficiently long ITI, the latency prolongation to the first three or four stimuli in a train was rapid. It was similar for trains differing in number of stimuli. After the first three or four stimuli, there was a more gradual latency prolongation as a function of stimulus number. Shorter ITIs had the effect of prolonging the latencies to all the stimuli in the trains, reducing the rate of latency prolongation over the first few stimuli, and causing responses to trains of different length to differ (e.g., two click train responses were shorter latency than four click train responses). An unexpected result was the latency prolongation of wave Vs after the presentation of the stimulus trains. In response to a train of clicks, there seems to be a rapid increase in wave V latency to the first few clicks in the train followed by a more gradual latency prolongation to subsequent clicks in the train.