Joint Synchronization of Vision and Hearing in the Brain

Article: How Our Brains Sync Hearing With Vision
Source: McGill University (Canada), via Technology Networks
Published: May 11, 2021

Fast and slow brain waves in auditory and visual brain regions
enable temporal recalibration of audiovisual stimuli

Physics tells us that light and sound travel at different speeds. Yet, visual and sound input from the same source arriving at our sense organs are then perceived as synchronous by the brain, even though they are processed at different speeds. The brain accounts for this difference through tricks such as temporal recalibration, altering our sense of time to synchronize the joint perception of sound and vision. This recalibration depends on brain signals constantly adapting to the environment to sample, order, and associate sensory inputs. Researchers in Canada used magnetoencephalography (MEG) to image the brain waves of volunteers asked to view short flashes of light paired with sounds with a variety of delays. The participants were then asked to report whether they thought both happened at the same time. The scientists found that the volunteers' perception of simultaneity in an audio-visual pair of stimuli was strongly affected by their perception of simultaneity in the preceding pair. For example, an audio-visual stimulus pair that was perceived as asynchronous might be followed by perceiving the next audio-visual stimulus pair as synchronous, even when it's not. The MEG signals revealed that such active temporal recalibration is the result of a unique interaction between fast and slow brain waves in auditory and visual regions of the brain, with the faster oscillations riding on top of slower fluctuations to create discrete and ordered time slots to register the order of sensory inputs. The relative delay between neural auditory and visual time slots, in turn, illustrates a dynamic process that constantly adapts to each participant’s recent exposure to audiovisual perception, ultimately resulting in judgments of perceived simultaneity of audiovisual input. The neurophysiological mechanisms of temporal recalibration may be relevant in disorders that affect audio and other sensory perception, such as in autism and schizophrenia.

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Lennert T, Samiee S and Baillet S. "Coupled oscillations enable rapid temporal recalibration to audiovisual asynchrony." Communications Biology.  4(1):1-12. 11 May 2021. https://doi.org/10.1038/s42003-021-02087-0