Category-specific interference of object recognition with biological motion perception.

The rapid and detailed recognition of human action from point-light displays is a remarkable ability and very robust against masking by motion signals. However, recognition of biological motion is strongly impaired when the typical point lights are replaced by pictures of complex objects. In a reaction time task and a detection in noise task, we asked subjects to decide if the walking direction is forward or backward. We found that complex objects as local elements impaired performance. When we compared different object categories, we found that human shapes as local objects gave more impairment than any other tested object category. Inverting or scrambling the human shapes restored the performance of walking perception. These results demonstrate an interference between object perception and biological motion recognition caused by shared processing capacities.