Rhythmic Modulation of Visual Perception by Continuous Rhythmic Auditory Stimulation.

At any given moment our sensory systems receive multiple, often rhythmic, inputs from the environment. Processing of temporally structured events in one sensory modality can guide both behavioral and neural processing of events in other sensory modalities, but whether this occurs remains unclear. Here, we used human electroencephalography (EEG) to test the cross-modal influences of a continuous auditory frequency-modulated (FM) sound on visual perception and visual cortical activity. We report systematic fluctuations in perceptual discrimination of brief visual stimuli in line with the phase of the FM-sound. We further show that this rhythmic modulation in visual perception is related to an accompanying rhythmic modulation of neural activity recorded over visual areas. Importantly, in our task, perceptual and neural visual modulations occurred without any abrupt and salient onsets in the energy of the auditory stimulation and without any rhythmic structure in the visual stimulus. As such, the results provide a critical validation for the existence and functional role of cross-modal entrainment and demonstrates its utility for organizing the perception of multisensory stimulation in the natural environment.SIGNIFICANCE STATEMENT Our sensory environment is filled with rhythmic structures that are often multi-sensory in nature. Here, we show that the alignment of neural activity to the phase of an auditory frequency-modulated (FM) sound has cross-modal consequences for vision: yielding systematic fluctuations in perceptual discrimination of brief visual stimuli that are mediated by accompanying rhythmic modulation of neural activity recorded over visual areas. These cross-modal effects on visual neural activity and perception occurred without any abrupt and salient onsets in the energy of the auditory stimulation and without any rhythmic structure in the visual stimulus. The current work shows that continuous auditory fluctuations in the natural environment can provide a pacing signal for neural activity and perception across the senses.

Prior expectation mediates neural adaptation to repeated sounds in the auditory cortex: an MEG study.

Repetition suppression, the phenomenon that the second presentation of a stimulus attenuates neural activity, is typically viewed as an automatic consequence of repeated stimulus presentation. However, a recent neuroimaging study has suggested that repetition suppression may be driven by top-down expectations. Here we examined whether and when repetition suppression can be modulated by top-down expectation. Participants listened to auditory stimuli in blocks where tone repetitions were either expected or unexpected, while we recorded ongoing neural activity using magnetoencephalography. We found robust repetition suppression in the auditory cortex for repeated tones. Interestingly, this reduction was significantly larger for expected than unexpected repetitions, both in terms of evoked activity and gamma-band synchrony. These findings indicate a role of top-down expectation in generating repetition suppression and are in line with predictive coding models of perception, in which the difference between expected and actual input is propagated from lower to higher cortical areas.

Tactile expectation modulates pre-stimulus beta-band oscillations in human sensorimotor cortex.

Neuronal oscillations are postulated to play a fundamental role in top-down processes of expectation. We used magnetoencephalography (MEG) to investigate whether expectation of a tactile event involves a pre-stimulus modulation of neuronal oscillations in human somatosensory cortex. In a bimodal attention paradigm, participants were presented with a predictable spatio-temporal pattern of lateralized tactile stimulations and simultaneously occurring non-lateralized auditory stimuli. Before the onset of a series of such combined audio-tactile stimuli, a cue was presented that indicated the sensory stream that had to be attended. By investigating lateralized patterns of oscillatory activity, we were able to study both attentive (when the tactile stream was attended) and non-attentive (when the auditory stream was attended) tactile expectations. For both attention conditions, we observed a lateralized modulation of the amplitude of beta band oscillations prior to a predictable - and accordingly lateralized - tactile stimulus. As such, we show that anticipatory modulation of ongoing oscillatory activity is not restricted to attended sensory events. Attention did enlarge the size of this modulation. We argue that this modulation constitutes a suppression of beta oscillations that originate at least partly from primary somatosensory cortex (S1) contralateral to the expected stimulation. We discuss our results in the light of the hypothesis that ongoing beta oscillations over sensorimotor cortex reflect a brain state in which neuronal processing efficacy is low. Pre-stimulus suppression of these oscillations then prepares the system for future processing. This shows that perception is an active process that starts even prior to sensation.