Biology subjects

Schyns, P. G.

Publications and source records attributed to Schyns, P. G..

4 recordsLinked to original sources

bioRxiv2018

Neural Processing of the Same, Behaviourally Relevant Face Features is Delayed by 40 ms in Healthy Ageing

Fast and accurate face processing is critical for everyday social interactions, but it declines and becomes delayed with age, as measured by both neural and behavioural responses. Here, we addressed the critical challenge of understanding how ageing changes neural information processing mechanisms to delay behaviour. Young (20-36 years) and older (60-86 years) adults performed the basic social interaction task detecting a face vs. noise while we recorded their electroencephalogram (EEG). In each participant, using a new information theoretic framework we reconstructed the features supporting face detection behaviour, and also where, when and how EEG activity represents them. We found that occipital-temporal pathway activity dynamically represents the eyes of the face images for behaviour [~]170 ms post-stimulus, with a 40 ms delay in older adults that underlies their 200 ms behavioural deficit of slower reaction times. Our results therefore demonstrate how ageing can change neural information processing mechanisms that underlie behavioural slow down.\n\nAuthor summaryOlder adults are consistently slower than young adults in a variety of behavioural perceptual tasks. So far, it has been unclear if the underlying cause of the behavioural delay relates to attentional or perceptual differences in encoding visual information, or slower neural processing speed, or other neural factors. Our study addresses these questions by showing that in a basic social interaction task (discriminating faces from noise), young and older adults encoded the same visual information (eyes of the face) to perform the task. Moreover, early brain activity (within 200 ms following stimulus onset) encoded the same visual information (again, eyes of the face) in both groups, but was delayed and weaker in older adults. These early delays in information encoding were directly related to the observed behavioural slowing in older adults, showing that differences in early perceptual brain processes can contribute to the motor response.

neuroscience↗

bioRxiv2017

Entrained audiovisual speech integration implemented by two independent computational mechanisms: Redundancy in left posterior superior temporal gyrus and Synergy in left motor cortex

Information integration is fundamental to many aspects of human behavior, and yet its neural mechanism remains to be understood. For example, during face-to-face communication we know that the brain integrates the auditory and visual inputs but we do not yet understand where and how such integration mechanisms support speech comprehension. Here we show that two independent mechanisms forge audiovisual representations for speech comprehension in different brain regions. With a novel information theoretic measure, we found that theta (3-7 Hz) oscillations in the posterior superior temporal gyrus/sulcus (pSTG/S) code speech information that is common (i.e. redundant) to the auditory and visual inputs whereas the same oscillations in left motor and inferior temporal cortex code synergistic information between the same inputs. Importantly, redundant coding in the left pSTG/S and synergistic coding in the left motor cortex predict behavior - i.e. speech comprehension performance. Our findings therefore demonstrate that processes classically described as integration effectively reflect independent mechanisms that occur in different brain regions to support audiovisual speech comprehension.

neuroscience↗

bioRxiv2017

Efficient Information Contents Flow Down from Memory to Predict the Identity of Faces

In the sciences of cognition, an influential idea is that the brain makes predictions about incoming sensory information to reduce inherent ambiguity. In the visual hierarchy, this implies that information content originating in memory-the identity of a face-propagates down to disambiguate incoming stimulus information. However, understanding this powerful prediction-for-recognition mechanism will remain elusive until we uncover the content of the information propagating down from memory. Here, we address this foundational limitation with a task ubiquitous to humans-familiar face identification. We developed a unique computer graphics platform that combines a generative model of random face identity information with the subjectivity of perception. In 14 individual participants, we reverse engineered the predicted information contents propagating down from memory to identify 4 familiar faces. In a follow-up validation, we used the predicted face information to synthesize the identity of new faces and confirmed the causal role of the predictions in face identification. We show these predictions comprise both local 3D surface patches, such as a particularly thin and pointy nose combined with a square chin and a prominent brow, or more global surface characteristics, such as a longer or broader face. Further analyses reveal that the predicted contents are efficient because they represent objective features that maximally distinguish each identity from a model norm. Our results reveal the contents that propagate down the visual hierarchy from memory, showing this coding scheme is efficient and compatible with norm-based coding, with implications for mechanistic accounts of brain and machine intelligence.

neuroscience↗

bioRxiv2016

Contributions of local speech encoding and functional connectivity to audio-visual speech integration

Seeing a speakers face enhances speech intelligibility in adverse environments. We investigated the underlying network mechanisms by quantifying local speech representations and directed connectivity in MEG data obtained while human participants listened to speech of varying acoustic SNR and visual context. During high acoustic SNR speech encoding by entrained brain activity was strong in temporal and inferior frontal cortex, while during low SNR strong entrainment emerged in premotor and superior frontal cortex. These changes in local encoding were accompanied by changes in directed connectivity along the ventral stream and the auditory-premotor axis. Importantly, the behavioural benefit arising from seeing the speaker's face was not predicted by changes in local encoding but rather by enhanced functional connectivity between temporal and inferior frontal cortex. Our results demonstrate a role of auditory-motor interactions in visual speech representations and suggest that functional connectivity along the ventral pathway facilitates speech comprehension in multisensory environments.

neuroscience↗