Binaural interaction in auditory brainstem responses of mentally retarded and nonretarded individuals.

The short-latency auditory brainstem responses of institutionalized mentally retarded individuals (Down syndrome and unknown etiology) and nonretarded control persons were recorded. The results showed that retarded individuals differed in the clarity of initial auditory brainstem response waves (I and II). Down syndrome individuals had significantly smaller auditory brainstem response amplitudes (Waves II and III) when compared with retarded individuals of unknown etiology. Down syndrome individuals also had significantly shorter latencies (Waves III and V) and shorter interwave conduction times (III-I and V-I) when compared with retarded individuals of unknown etiology. Retarded individuals did not differ from control subjects when amplitudes of binaural auditory brainstem responses were compared to the computer summation of such responses evoked by left and right ear stimulation; however, there was evidence for a general binaural interaction effect.