AUDITORY-EVOKED BRAIN-STEM AND MIDDLE LATENCY RESPONSES IN MACACA-MULATTA AND HUMANS

Early (ABRs) and middle (MLRs) surface-recorded auditory evoked potent ials were compared in eight adult monkeys (Macaca mulatta) and eight a dult humans. Responses whose probable generators were the cochlear nuc leus and lateral lemniscus were of shorter latency and larger amplitud e in monkeys. Relative to humans, ABR response latencies in monkeys we re less affected by stimulus intensity, stimulus rate, and masker leve l. In contrast, monkey amplitudes were relatively more affected by tho se same stimulus parameters. The most prominent MLR wave was longer in latency and greater in amplitude in humans than the homologous wave i n monkeys. The reduction in amplitude of that wave with increasing rat e was greater for humans than monkeys. Temporal interactions (the effe ct of prior stimuli on the response to current stimulation) were inves tigated from a non-linear systems identification framework using maxim um length sequences (MLSs). Both monkey and human auditory systems wer e second and probably third-order systems at the levels assessed. As t he separations between the stimulus pulses decreased, evidence for tem poral interactions became more prominent, reached a maximum, and then decreased with further decreases in stimulus pulse separation. At the highest stimulus rates presented, variations in temporal spacing among stimuli had less of an effect on monkey than human evoked responses.