Residual perception of biological motion in cortical blindness

Abstract

From birth, the human visual system shows a remarkable sensitivity for perceiving biological motion. This visual ability relies on a distributed network of brain regions and can be preserved even after damage of high-level ventral visual areas. However, it remains unknown whether this critical biological skill can withstand the loss of vision following bilateral striate damage. To address this question, we tested the categorization of human and animal biological motion in BC, a rare case of cortical blindness after anoxia-induced bilateral striate damage. The severity of his impairment, encompassing various aspects of vision (i.e., color, shape, face, and object recognition) and causing blind-like behavior, contrasts with a residual ability to process motion. We presented BC with static or dynamic point-light displays (PLDs) of human or animal walkers. These stimuli were presented either individually, or in pairs in two alternative forced choice (2AFC) tasks. When confronted with individual PLDs, the patient was unable to categorize the stimuli, irrespective of whether they were static or dynamic. In the 2AFC task, BC exhibited appropriate eye movements 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 biological motion 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. Finally, our findings reinforce the view that the neural network processing biological motion can efficiently operate despite severely impaired low-level vision, positing our natural predisposition for processing dynamicity in biological agents as a robust feature of human vision.

Comparable search efficiency for human and animal targets in the context of natural scenes

“…This motion similarity may confer some processing advantage for animals relative to machines, as captured by the shorter fixation duration found for animal targets in this experiment. This advantage is in line with the biological advantage found using impoverished point-light stimuli of humans and animals, in which predominantly motion information is available (e.g., Pavlova, Krageloh-Mann, Sokolov, & Birbaumer, 2001;Ruffieux et al, 2016;Shi, Weng, He, & Jiang, 2010;Troje & Westhoff, 2006). As we previously suggested (Mayer et al, 2015(Mayer et al, , 2017, the shorter fixation duration may reflect faster processing of animal than of machine targets.…”

“…Second, the familiarity of the actions may be important. Previous studies had used a limited number of common actions, such as running versus walking (Cavanagh et al, 2001;Papeo et al, 2017;Pinto & Shiffrar, 2009;Ruffieux et al, 2016;Troje & Westhoff, 2006). We used videos of humans and animals that performed a wider variety of both familiar and less familiar actions-for example, a person rolling on the ground, a person doing jumping jacks, a kangaroo moving its arms, and a chimpanzee climbing a tree.…”

Visual Neuropsychology in Development: Anatomo-Functional Brain Mechanisms of Action/Perception Binding in Health and Disease

“…Typically associated with an extrastriate brain lesion (Zihl et al, 1983;Cooper et al, 2012;Otsuka-Hirota et al, 2014), akinetopsia can indeed be experimentally induced by inhibiting V5 (Beckers and Hömberg, 1992), as well as V1 but at a smaller degree and with specific timing with respect to the visual stimulus (Beckers and Hömberg, 1992). This is in line with the observation that sensitivity to motion can survive cortical blindness (Ruffieux et al, 2016), also in children that present a congenital, but not acquired, lesion of V1 (Tinelli et al, 2013). While blindness to first-order motion (e.g., luminance-based) would result from lesions in V2/V3, blindness to second-order motion (e.g., contrast-based) would derive from lesions in V4/V5 (Cowey et al, 2006).…”

A decisional space account of saccadic reaction times towards personally familiar faces

“…Specifically, we proposed that procedural aspects effectively constrain the decisional space within which observers perform a task, which in turn determines measured behavior (Ramon, in press; Ramon et al, in press; see also Ramon & Rossion, 2010;Ramon, Busigny, Gosselin & Rossion, 2017;Ruffieux, Ramon, Lao, Colombo, Stacchi et al, 2017). To test this assumption, we measured observers' saccadic RTs across three experiments.…”