Human long-latency potentials evoked by monaural interruptions of a binaural click train: connection to sound lateralization based on interaural intensity differences.

In 9 subjects with normal hearing, monaural offset (MO) responses in the long-latency range were recorded with and without an ongoing sound (click train at a rate of 250/s) at the opposite ear. In the latter case MOs were perceived simply as termination of a sound. In the former case, however, the abrupt transition from binaural to monaural (BM) stimulation was perceived as a shift of the fused image from the center to either side. Therefore, the fairly large difference potential obtained by subtracting the MO response from the BM response was evaluated as the cortical response to stimulation of the sound lateralization mechanism based on interaural intensity differences. These center-to-side responses, which could be characterized by an N1-P2 wave sequence at latencies of 120 and 220 ms, respectively, were compared with the auditory onset responses also recorded from the same subjects by means of a sequential stimulation paradigm. The scalp topography of the N1 components in all these responses recorded simultaneously from frontocentral, parietocentral and two superior temporal electrodes with a neck reference is discussed.