EFFECT OF STIMULUS LEVEL AND FREQUENCY ON ABR AND MLR BINAURAL INTERACTION IN HUMAN NEONATES

Auditory brainstem (ABR) and middle latency (MLR) responses were evoke d by click and tone-burst stimuli from human neonates. Electrophysiolo gic evidence of binaural interaction was measured by subtracting wavef orms obtained for binaural stimulus conditions from waveforms obtained for the sum of right ear monaural and left ear monaural stimulus cond itions. The effects of stimulus level and stimulus frequency on binaur al interaction were evaluated by measuring the number, latency and amp litude of components found in the derived binaural interaction wavefor m, that is, binaural interaction components (BIG). BICs were more prev alent in the latency range of ABRs than for MLRs. Click and tonal stim uli were equally effective for deriving ABR-BICs, while tone-bursts we re somewhat less effective than clicks for deriving MLR-BICs. Stimulus -response dependencies for ABR and MLR component latencies were appare nt in monaural, binaural and binaural interaction waveforms. Normalize d amplitudes for BICs showed that low-frequency tone-burst stimuli res ulted in the largest values compared to click and high-frequency tonal stimuli. Comparison of these results with published results from adul ts demonstrated immaturity of binaural interaction in neonates.