Residual Perception of Biological Motion in Cortical Blindness

Abstract

The ability to perceive biological motion (BM) relies on a distributed network of brain regions and can be preserved after damage to high-level visual areas. However, whether it can withstand the loss of vision following bilateral striate damage remains unknown. Here we tested categorization of human and animal BM in BC, a rare case of cortical blindness after anoxia-induced bilateral striate damage. The severity of his impairment, encompassing various aspects of vision and causing blind-like behavior, contrasts with a residual ability to process motion (for a video demonstration see perso.unifr.ch/roberto.caldara/VSS/BC_patient.mov). We presented BC with static or dynamic point-light displays (PLDs) of human or animal walkers. These stimuli were presented individually, or in pairs in two alternative forced choice (2AFC) tasks. Confronted with individual PLDs, BC was unable to categorize the stimuli, irrespective of whether they were static or dynamic. In the 2AFC task, BC exhibited appropriate gaze towards diagnostic information, but performed at chance level with static PLDs, in stark contrast to his ability to efficiently categorize dynamic biological agents. This striking ability to categorize BM provided top-down information is important for at least two reasons. Firstly, it emphasizes the importance of assessing patients' (visual) abilities across a range of task constraints, which can reveal potential residual abilities that may in turn represent a key feature for patient rehabilitation. Our findings reinforce the view that the BM processing network can operate despite severely impaired low-level vision, emphasizing that processing dynamicity in biological agents is a robust feature of human vision.

Meeting abstract presented at VSS 2017