The neural mechanisms of audiotactile binding depend on asynchrony

Asynchrony is a critical cue informing the brain whether sensory signals are caused by a common source and should be integrated or segregated. This psychophysics-electroencephalography (EEG) study investigated the influence of asynchrony on how the brain binds audiotactile (AT) signals to enable faster responses in a redundant target paradigm. Human participants actively responded (psychophysics) or passively attended (EEG) to noise bursts, 'taps-to-the-face', and their AT combinations at seven AT asynchronies: 0, ±20, ±70, and ±500ms. Behaviourally, observers were faster at detecting AT than unisensory stimuli within a temporal integration window: the redundant target effect was maximal for synchronous stimuli and declined within a ≤70ms AT asynchrony. EEG revealed a cascade of AT interactions that relied on different neural mechanisms depending on AT asynchrony. At small (≤20ms) asynchronies, AT interactions arose for evoked response potentials (ERPs) at 110ms and ~400ms post-stimulus. Selectively at ±70ms asynchronies AT interactions were observed for the P200 ERP, theta-band inter-trial coherence (ITC) and power at ~200ms poststimulus. In conclusion, AT binding was mediated by distinct neural mechanisms depending on the asynchrony of the AT signals. Early AT interactions in ERPs and theta-band ITC and power were critical for the behavioural response facilitation within a ≤±70ms temporal integration window.