Binaural interaction measured behaviorally and electrophysiologically in young and old adults.

12 young men (mean age = 39.1 years) and 12 older men (mean age = 69.4 years) presenting some degree of sensorineural hearing loss were chosen so that the two groups were audiometrically matched. Behavioral tests of binaural interaction (BI) included binaural fusion, rapidly alternating speech perception, and masking level difference (at 500 Hz). There was a tendency toward better performance by the younger subjects for each of these tests, but these comparisons fell short of statistical significance. Auditory brainstem responses (ABRs) and middle-latency responses (MLRs) to clicks were recorded in both monaural and binaural modes, with off-line derivation of BI components. Latencies of wave V (in ABR) and waves Pa and Nb (in MLR) were prolonged in the older subjects for all conditions; this effect was independent of degree of hearing loss. BI components did not differ substantially between the two groups, except for a 0.45-ms latency difference for the 'N1' peak, as expected from the raw ABR data. MLRs for both groups showed a pattern of BI which was different from that seen in young subjects with normal hearing, in that latency for wave Pa in MLR was not reduced in the binaural condition. The young subjects showed the expected reduction of binaural wave Pa amplitude compared to monaural sum responses, while the older subjects, as a group, did not. No significant correlations were found between behavioral and electrophysiological tests.