Modulations of Single-Trial Interactions between the Auditory and the Visual Cortex during Prolonged Exposure to Audiovisual Stimuli with Fixed Stimulus Onset Asynchrony

The perception of simultaneity between auditory and visual stimuli is of crucial importance for audiovisual integration. However, the speeds of signal transmission differ between the auditory and the visual modalities and these differences have been shown to depend on multiple factors. To maintain the information about the temporal congruity of auditory and visual stimuli, flexible compensation mechanisms are required. Several behavioral studies demonstrated that the perceptual system is able to adaptively recalibrate itself to audio-visual temporal asynchronies [33,94]. Here we explored the adaptation to audio-visual temporal asynchronies at the cortical level. Tone and light stimuli at the same constant stimulus-onset-asynchrony were presented repeatedly to awake, passively listening, Mongolian gerbils. During stimulation the local field potential was recorded from electrodes implanted into the auditory and the visual cortices. The dynamics of the interactions between auditory and visual cortex were examined using the Directed Transfer Function (DTF; [42]). With increasing number of stimulus repetitions the averaged evoked response of the Directed Transfer Function exhibited gradual changes in amplitude. A single-trial analysis indicated that the adaptations observed in the all-trial average were due to modulations of the amplitude of the single-trial DTFs hut not to alterations in the trial-to-trial dynamics of DTF peaks.