Researchers from University College London (UCL), Carnegie Mellon University and UC San Diego have found that the ability to understand different movements, such as walking and jumping, engages different brain mechanisms from those that are used to recognize who is initiating the action (Gilaie-Dotan, S., Saygin, A.P., Lorenzi, L.J., Rees,G. and Behrmann, M). In the study, individuals with lesions to the ventral aspects of the visual pathway evinced normal biological motion perception despite their marked impairments in form perception.
The analysis revealed that the ventral aspects of the form pathway (e.g., fusiform regions, ventral extrastriate body area) are not critical for biological motion perception. These counterintuitive findings indicate that biological motion can be perceived and processed normally even when the ability to perceive the form or the actor executing the movements is impaired. The study illustrates for the first time how individuals with prosopagnosia, or face blindness, are still able to recognize other people's movements. The investigators hypothesize that the role of these ventral regions is to provide enhanced multiview/posture representations of the moving person rather than to represent biological motion perception per se.
Identifying the movements of those around us is fundamental for many daily activities, such as recognizing actions, detecting predators, and interacting with others socially. A key question concerns the neurobiological substrates underlying biological motion perception. Although the ventral "form" visual cortex is standardly activated by biologically moving stimuli, whether these activations are functionally critical for biological motion perception or are epiphenomenal remains unknown. To address this question, the researchers examined whether focal damage to regions of the ventral visual cortex, resulting in significant deficits in form perception, adversely affects biological motion perception.
Six patients with damage to the ventral cortex were tested with sensitive point-light display paradigms. All patients were able to recognize unmasked point-light displays and their perceptual thresholds were not significantly different from those of three different control groups, one of which comprised brain-damaged patients with spared ventral cortex (n > 50). Importantly, these six patients performed significantly better than patients with damage to regions critical for biological motion perception. To assess the necessary contribution of different regions in the ventral pathway to biological motion perception, the researchers complement the behavioral findings with a fine-grained comparison between the lesion location and extent (see Figure), and the cortical regions standardly implicated in biological motion processing. This analysis revealed that the ventral aspects of the form pathway (e.g., fusiform regions, ventral extrastriate body area) are not critical for biological motion perception.
Gilaie-Dotan, S., Saygin, A.P., Lorenzi, L.J., Rees,G. and Behrmann, M. (2014). Ventral aspect of the visual form pathway is not critical for the perception of biological motion. Proceedings of the National Academy of Sciences (PNAS); 112(4). E361-E370, doi: 10.1073/pnas.1414974112. Link to article