Rhythmic gain control during supramodal integration of approximate number.

According to one view, neural oscillations structure information processing in time, determining whether sensory inputs have a strong or weak impact on behavior. Recent work showed that during sequential integration of visual inputs, stimuli that fall in the preferred phase of slow (1-3 Hz), endogenous EEG activity carry greater weight in subsequent judgment. Here, we asked two questions. Firstly, is this phenomenon modality-specific, or is it supramodal? Secondly, does this effect occur at the level of sequential encoding, or only during decision formation? We analyzed scalp EEG recordings from healthy human participants while they compared the approximate number of visual, auditory or somatosensory pulses in two successive intervals (N1 and N2). Despite differences in activity evoked in different domains, a common, slowly-oscillating (~3 Hz) choice-predictive signal was observed in all three modalities with a maximum coincident with pulse onset. Critically, this signal was present during N2 (when a decision was being formed) but absent during N1 (when perceptual information was encoded, but no decision could be made). In other words, rhythmic gain control during sequential processing is a supramodal phenomenon that occurs while information is integrated towards a categorical decision.