Spatial biases in motion extrapolation for manual interception.

The exact mechanisms by which humans control the manual interception of moving targets are currently unknown. Here, the authors explored the behaviors associated with the spatial control for manual interception. The examined task required controlling a cursor to intercept moving targets on a touch screen. They explored the effects of target motion direction, curvature and occlusion on manual interception. They observed occlusion-dependent spatial errors and arrival times for curved and diagonal trajectories (larger errors and earlier arrival of the finger at its final position with longer occlusion). These effects were particularly apparent for targets moving away from screen center at interception due to curve. In a follow-up experiment, the authors showed that the outward curve effects on spatial errors were absent because the associated trajectories appears to move toward positions that participants could expect the target to never reach. Their analyses also revealed occlusion-dependent spatial errors for diagonal trajectories, which is the well-known angle-of-approach effect. Follow-up experiments demonstrated that this effect was not due to the central initial cursor position acting as a visual reference point or the initial ocular pursuit. Most importantly, the angle-of-approach effect persisted in a judgment task. The authors thus concluded that this effect does not stem from online information-based modulations of movement speed, but from target information used to control aiming (i.e., movement direction). Moreover, processing for diagonal target motion appears to be biased toward straight downward. Public Significance Statement This study examines the control of manual interception, for a range of target trajectories, using visual occlusion. The authors show that occlusion causes spatial biases in the movements because unseen target motion is not fully accounted for. Participants quite accurately intercepted targets moving on straight trajectories and targets continuously visible; spatial biases arose, however, when unseen target motion must be accounted for. Because these effects were present irrespective of the time pressure inherent to manual interception, the authors interpret these to originate from target information used to control where to move rather than how fast to move. This research has implications in sports training, suggesting that the usefulness of visual occlusion training may be dependent on exactly how occluded objects are moving.