Reduced perceptual sensitivity for biological motion in paraplegia patients

Many physiological and psychophysical studies suggest that the perception and execution of movement may be linked [1–4]. Here we ask whether severe impairment of locomotion could impact on the capacity to perceive human locomotion. We measured sensitivity for the perception of point-light walkers — animation sequences of human biological motion portrayed by only the joints — in patients with severe spinal injury. These patients showed a huge (nearly three-fold) reduction of sensitivity for detecting and for discriminating the direction of biological motion compared with healthy controls, and also a smaller (∼40%) reduction in sensitivity to simple translational motion. However, they showed no statistically significant reduction in contrast sensitivity for discriminating the orientation of static gratings. The results point to a strong interaction between perceiving and producing motion, implicating shared algorithms and neural mechanisms.