Oscillatory properties of functional connections between sensory areas mediate crossmodal illusory perception

The presentation of simple auditory stimuli can significantly impact visual processing and even induce visual illusions, such as the auditory-induced Double Flash Illusion (DFI). These crossmodal processes have been shown to be driven by occipital oscillatory activity within the alpha band. Whether this phenomenon is network specific or can be generalized to other sensory interactions remains unknown. The aim of the current study was to test whether crossmodal interactions between somatosensory-to-visual areas leading to the same (but tactile-induced) DFI share similar properties to the auditory-DFI. We hypothesized that if the effects are mediated by the oscillatory properties of early visual areas per se then the two versions of the illusion should be subtended by the same neurophysiological mechanism (i.e. the speed of alpha frequency). Alternatively, if the oscillatory activity in visual areas predicting this phenomenon is dependent on the specific neural network involved, then it should reflect network-specific oscillatory properties. In line with the latter, results recorded in humans (both genders) show a network-specific oscillatory profile linking the auditory-DFI to occipital alpha oscillations, replicating previous findings, and tactile-DFI to occipital beta oscillations, a rhythm typical of somatosensory processes. These frequency-specific effects are observed for visual (but not auditory or somatosensory) areas and account for auditory-visual connectivity in the alpha band and somatosensory-visual connectivity in the beta band. We conclude that task-dependent visual oscillations reflect network-specific oscillatory properties favouring optimal, directional neural communication timing for sensory binding.