Human frequency following response correlates of interaural time difference and time-intensity trade

The binaural interaction component (BIC) is the difference between the sum of two independent monaural responses and a binaural response. The presence of an electrophysiologic correlate of lateralization as exhibited in the BIC of the human frequency following response (FFR) evoked by 500 Hz tone bursts and the alterations of the BIC as a function of interaural time differences (ITD) and time-intensity trading was investigated. The FFR-BIC was demonstrated. The FFR changes correlated with our psychoacoustic results suggesting that the FFR-BIC and the binaural (BIN) FFR may be related to lateralization of the fused image of a low frequency sound. The results related specifically to the reduction in the amplitude of the BIN FFR and the FFR-BIC components as the ITD increased and also to the increase in the amplitude of the BIN FFR and the FFR-BIC components as increasing IID imposed on an ITD lateralized sound. The nature of these alterations in the BIN FFR and the FFR-BIC components are consistent with the idea of non-linear neural interactive processes within the rostral brainstem mediating these changes.