Spatio-temporal frequency characteristics of intersensory components in audiovisually evoked potentials

Perception of the external world is based on complex neural processes allowing for combination of sensory experiences from different modalities. Audiovisual (AV) integration is discussed in this paper on the basis of the intersensory component (IC), which is the part of the multisensory-evoked potential that is not explained by linear summation of the unisensory-evoked potentials. It was predicted that audiovisual ICs can be extracted, localized, and differentiated by means of wavelet-based frequency analysis. Healthy, right-handed subjects (n = 15) were instructed to view and listen to presented stimuli (A: auditory; V: visual; and AV: audiovisual). Electroencephalographic data was analyzed offline by means of wavelet transformation utilizing quadratic B-spline mother wavelets. Cross-modal interaction was investigated by subtracting wavelet responses to unimodal stimuli (A, V) alone from the wavelet responses to the combined stimuli (AV; i.e., interaction = AV - (A + V)). These difference waveforms revealed the phase-locked fraction of ICs further characterized by frequency-band and location.