Transversal hand action in the frontoparallel plane biases the perception of bistable visual motion. This has been called action capture. In daily behaviour, however, hand action in a ‘radial’ direction from the head might be more important, because we frequently reach our hand for an object in front of us while guiding the action with vision. The purpose of this study was to measure the strength of action capture in the radial direction. Horizontal luminance gratings were placed above and below the fixation point. Binocular disparity, perspective contour, and spatial frequency gradient cues were attached to the gratings so that they simulated the ‘ceiling’ and the ‘floor’ of a long corridor. The display was reflected on a tilted mirror to face upward. The subject looked into the display and moved his/her dominant hand toward, or away from, the face behind the mirror. Just after the action onset, detected by the computer, one of the two gratings (the ceiling or the floor) flickered in short period to simulate bistable visual motion in depth (approaching or departing). The subject indicated the perceived motion direction in the frontoparallel plane using a 2AFC (upward or downward) method. The results showed that perceived motion was significantly biased to the ‘departing’ direction when the hand moved ‘away from’ the face, and it was biased to the ‘approaching’ direction when the hand moved ‘toward’ it. It is concluded that action capture occurs not only in transversal but also in radial movements.
Interactions between cues to visual motion in depth