Visual acceleration and spatial distortion in right brain-damaged patients.

A subset of right brain-damaged patients shows leftward overextension in the line extension task. It has been argued that this deficit can be attributed to a distortion of the metric structure of perceived space (spatial anisometry). We investigated whether spatial distortion of static stimuli is associated with a corresponding misperception of perceived acceleration of moving stimuli. Seven right brain-damaged patients with spatial anisometry and two control groups were presented with stimuli moving leftwards or rightwards along the horizontal axis at different rates of acceleration. They were asked to estimate whether the target accelerated or decelerated. The anisometric group judged the perceived acceleration of leftward motions as less than that of rightward motions. The magnitude of the misperception of acceleration correlated positively with relative left overextension in the line extension task and with rightward displacement error in the line bisection task. This directional difference is in line with the predictions of the spatial anisometry hypothesis.