Biology subjects

Beauchamp, M. S.

Publications and source records attributed to Beauchamp, M. S..

3 recordsLinked to original sources

bioRxiv2018

Phase resetting in human auditory cortex to visual speech

Natural conversation is multisensory: when we can see the speakers face, visual speech cues influence our perception of what is being said. The neuronal basis of this phenomenon remains unclear, though there is indication that phase modulation of neuronal oscillations--ongoing excitability fluctuations of neuronal populations in the brain--provides a mechanistic contribution. Investigating this question using naturalistic audiovisual speech with intracranial recordings in humans, we show that neuronal populations in auditory cortex track the temporal dynamics of unisensory visual speech using the phase of their slow oscillations and phase-related modulations in high-frequency activity. Auditory cortex thus builds a representation of the speech streams envelope based on visual speech alone, at least in part by resetting the phase of its ongoing oscillations. Phase reset could amplify the representation of the speech stream and organize the information contained in neuronal activity patterns. SIGNIFICANCE STATEMENTWatching the speaker can facilitate our understanding of what is being said. The mechanisms responsible for this influence of visual cues on the processing of speech remain incompletely understood. We studied those mechanisms by recording the human brains electrical activity through electrodes implanted surgically inside the skull. We found that some regions of cerebral cortex that process auditory speech also respond to visual speech even when it is shown as a silent movie without a soundtrack. This response can occur through a reset of the phase of ongoing oscillations, which helps augment the response of auditory cortex to audiovisual speech. Our results contribute to discover the mechanisms by which the brain merges auditory and visual speech into a unitary perception.

neuroscience↗

bioRxiv2018

Face Viewing Behavior Predicts Multisensory Gain During Speech Perception

During face viewing, some individuals prefer to fixate the mouth while others fixate the eyes. Individuals who have a history of mouth fixation might have stronger associations between visual and auditory speech, resulting in improved comprehension. First, we measured eye movements during face-viewing and observed high interindividual variability in mouth fixation time. Next, we measured eye movements and comprehension during perception of noisy auditory speech with or without visual speech. When visual speech was present, participants primarily fixated the mouth, but derived substantial benefit compared to noisy auditory speech with high interindividual variability. The benefit of visual speech was predicted by the eye movements made during the initial face-viewing task, but not by eye movements during the noisy speech task. These findings suggest a link between eye movements during face viewing and audiovisual speech perception and suggest that individual histories of visual exposure shape abilities across cognitive domains.

neuroscience↗

bioRxiv2018

Rules Governing Perception of Multiple Phosphenes by Human Observers

Stimulation of single sites in primary visual cortex results in the perception of a small flash of light known as a phosphene. Little is known about how phosphenes from multiple electrodes can be combined to form perception of coherent patterns. Here we examine the percepts reported by human observers as various spatial configurations of 2 to 5 electrodes in visual cortex were stimulated simultaneously. When two electrodes were stimulated simultaneously, subjects reliably perceived either one or two phosphenes depending on the physical distance separating the electrodes. In cases where two phosphenes were perceived, they were located in the same visual field location as when the two electrodes were stimulated separately. Adding a third electrode produced similar results. In several subjects, we obtained combination of 4 to 5 electrodes that generated individual phosphenes when stimulated concurrently. Subjects were able to reliably discriminate between different multiple electrode stimulation patterns that were presented in random order. These results demonstrate that simple pattern information can be conveyed to subjects with surface electrodes spaced at millimeters apart on the cortex.

neuroscience↗