Recognizing approaching walkers: Neural decoding of person familiarity in cortical areas responsive to faces, bodies, and biological motion

- Neurally decoded familiarity of walkers in ventral and dorsal visual stream ROIs.
- Neural decoding occurred when walkers were most distant in the dorsal stream pSTS.
- Face- and body-selective regions decoded familiarity: bEBA, lFBA, rOFA, bOFA.
- Interactions among collections of face- and body-selective voxels for recognition.
- Widespread neural network signals the familiarity of a person in motion.

In natural viewing environments, we recognize other people as they move through the world. Behavioral studies indicate that the face, body, and gait all contribute to recognition. We examined the neural basis of person recognition using a decoding approach aimed at discriminating the patterns of neural activity elicited in response to seeing visually familiar versus unfamiliar people in motion. Participants learned 30 identities by viewing multiple videos of the people in action. Recognition was tested inside a functional magnetic resonance imaging (fMRI) scanner using 8-s videos of 60 people (30 learned and 30 novel) approaching from a distance (~13 m). Full brain images were taken while participants watched the approach. These images captured neural activity at four time points (TRs) corresponding to progressively closer views of the walker. We used pattern classification techniques to examine familiarity decoding in lateralized ROIs and the combination of left and right (bilateral) regions. Results showed accurate decoding of familiarity at the farthest distance in the bilateral posterior superior temporal sulcus (bpSTS). At a closer distance, familiarity was decoded in the bilateral extrastriate body area (bEBA) and left fusiform body area (lFBA). The most robust decoding was found in the time window during which the average behavioral recognition decision was made - and when the face came into clearer view. Multiple regions, including the right occipital face area (rOFA), bOFA, bFBA, bpSTS, and broadly distributed face- and body-selective voxels in the ventral temporal cortex decoded walker familiarity in this time window. At the closest distance, the lFBA decoded familiarity. These results reveal a broad system of ventral and dorsal visual areas that support person recognition from face, body, and gait. Although the face has been the focus of most person recognition studies, these findings remind us of the evolutionary advantage of being able to differentiate the people we know from strangers at a safe distance.