The emerging perceptual representation of faces decoded from human neuromagnetic recordings.

• ¹ Macquarie University, Cognitive Sciences, Australia
• ² University College London, U.K.

As highly social creatures, face perception is essential to daily human life. From the moment we turn our gaze to an individual, our brain begins to form a perceptual representation of the individual's face to promote recognition and ultimately guide our social interactions. In the present study we used a generative model of face perception, human behaviour, and a magnetoencephalography (MEG) decoding approach to study when and how the brain constructs a perceptual representation of a face. We first generated 18 individual face exemplars using a generative model of face perception that encodes faces using a range of metric features, e.g. eye width. In a behavioural experiment, we then measured the human capacity to discriminate faces for all possible pairwise comparisons between face exemplars. The behavioural data was then used to estimate a perceptual geometry of the face stimuli, which is described quantitatively in a dissimilarity matrix (DSM). Next, in a MEG experiment, we used a sliding window decoding approach to measure the neural discriminability between the face stimuli as a function of time (100Hz temporal resolution). The decoding analysis produced a set of time varying DSMs, which describe the brain's emerging representational geometry of the stimuli. To determine when the brain forms a perceptual representation of a face, we compared the perceptual geometry (from behaviour) to the time varying representational geometry of the stimuli in the brain. Our analysis found a significant correspondence between perception and the brain's representation 80ms after stimulus onset that peaked at 100ms. Our results show that the brain rapidly constructs a perceptual representation of a face; and the extremely short latency further suggests this representation is constructed using feed forward mechanisms. This early (fast) representation might underlie our capacity to rapidly recognize individuals and their emotional state, and to guide social interactions.