Journal Article

Perception of object motion in three-dimensional space induced by cast shadows

Nose, Izuru, Taira, Masato, Katsuyama, Narumi, Usui, Nobuo

2011

Overview

Cast shadows can be salient depth cues in three-dimensional (3D) vision. Using a motion illusion in which a ball is perceived to roll in depth on the bottom or to flow in the front plane depending on the slope of the trajectory of its cast shadow, we investigated cortical mechanisms underlying 3D vision based on cast shadows using fMRI techniques. When modified versions of the original illusion, in which the slope of the shadow trajectory (shadow slope) was changed in 5 steps from the same one as the ball trajectory to the horizontal, were presented to participants, their perceived ball trajectory shifted gradually from rolling on the bottom to floating in the front plane as the change of the shadow slope. This observation suggests that the perception of the ball trajectory in this illusion is strongly affected by the motion of the cast shadow. In the fMRI study, cortical activity during observation of the movies of the illusion was investigated. We found that the bilateral posterior-occipital sulcus (POS) and right ventral precuneus showed activation related to the perception of the ball trajectory induced by the cast shadows in the illusion. Of these areas, it was suggested that the right POS may be involved in the inferring of the ball trajectory by the given spatial relation between the ball and the shadow. Our present results suggest that the posterior portion of the medial parietal cortex may be involved in 3D vision by cast shadows. [Display omitted] ►Motion perception of an object is strongly affected by the motion of its cast shadow. ►Activity of hMT+ correlates with physical quantity of motion in visual stimulus. ►Activity of medial parietal cortex correlates with perceived object motion in 3D. ►Medial parietal cortex is involved in motion perception in 3D space by cast shadows.

• Publisher: Elsevier Inc,Elsevier Limited
• Subject: Adult / Behavior / Brain / Brain Mapping - methods / Cast shadow / Depth Perception - physiology / Female / fMRI / Frontal Lobe - physiology / Gyrus Cinguli - physiology / Humans / Magnetic Resonance Imaging - methods / Male / Motion / Motion Perception - physiology / Motion Pictures / NMR / Nuclear magnetic resonance / Parietal cortex / Parietal Lobe - physiology / Size Perception - physiology / Stereo vision / Temporal Lobe - physiology / Young Adult