Response asymmetry and binaural interaction in the auditory brain stem evoked response.

Asymmetry in the auditory brain stem evoked response (ABR) and its effect on measurements of binaural interaction were studied. Monaural and binaural ABRs were recorded from 24 normal hearing subjects at two sensation levels: 70 and 50 dB. Monaural responses were judged to be asymmetrical when the right response minus the left response resulted in a difference trace which was significantly greater than the level of the background noise in the ABR. It was found that sensation level significantly affected the frequency of monaural response asymmetry and that the amplitude of the derived binaural interaction component (BIC) was positively correlated with the degree of asymmetry present. Offsetting the asymmetry by introducing an interaural intensity difference resulted in a significant reduction in the amplitude of the BIC. It was concluded that the BIC is affected by factors other than those which can be attributed solely to binaural interaction.