Abstract
Interception requires positional and velocity estimates of moving targets. Local motion affects the perceived position and velocity of static and moving Gabor patches respectively. However, the effect of local motion on action has been addressed with static Gabors or Gabors that underwent global retinal motion due to eye movements. I here address how local and global motion of moving Gabors affect action initiation and movement time. Targets were Gabor patches (SF=0.9 c/deg) that rotated clockwise with six possible global tangential velocities (2.9, 4.8, 7.9, 21.4, 58 deg/s). Using each rotational speed as a reference without local motion, I obtained the corresponding global speed that resulted in the same perceived speed when local motion in the same and opposite directions were added. For a given rotating speed I thus obtained 3 perceptually similar local motion conditions: without, same and opposite. Subjects then intercepted Gabors under these different conditions by controlling the horizontal position of a cursor with a polling device (sample rate 120 Hz). The interception had to occur when the envelope was between two reference horizontal lines. The initial Gabor phase was randomized across trials to avoid using positional local information. I recorded the position of the Gabor when the action started and when the cursor crossed the Gabor’s path allowing to compute spatial and temporal errors and movement time. The position of the Gabors at action initiation was well explained by considering the local drift. That is, for a given rotational speed, subjects started moving when the target was at perceptually equivalent (but physically different) distances from the interception point. Interestingly, however, the movement time did not correlate with the perceived remaining time (considering local speed) but depended on the physical arrival time of the envelope. This reflects a different sensitivity to local motion for sensory and motor phases.
Meeting abstract presented at VSS 2013