[Evoked cortical potentials caused by short-term changes in interaural coherence].

Abstract

The purpose of this study was to examine the cortical potentials evoked by short-term changes of interaural time difference or by using two different noise generators. Patients describe a short-term change of lateralisation as a sensation, depending on the degree and duration of the signal change. To derive positive potentials, interaural time differences of about 100 microseconds require time constants for these short-term changes of lateralisation of about 40 ms; this value is reduced to 4 ms for 900 microseconds. When using two different noise generators minimal time constants between 2 and 4 ms are obtained. With growing interaural time difference or duration of signal change the amplitude of the cortical evoked potential is significantly increased. The differences in latency are not very pronounced. This holds true for the potentials evoked by the use of two different noise generators. Compared with results of changes in monaural intensity or frequency, it seems that the analysis of interaural signal variations takes place predominantly in cortical areas of the hearing organ. Our investigations of the brain stem support this assumption and underline the dominant influence of the cortex with regard to time resolution processes of binaural signals.