Multiple-object tracking and visually guided touch.

Multiple-object tracking (MOT) involves keeping track of the positions of multiple independent target items as they move among distractors. According to Pylyshyn (Cognition, 80, 127-158, 2001), the item individuation mechanism used in MOT is also used in visually guided touch. To test this, we compared single-task MOT (MOT alone) with dual-task MOT (MOT while touching items that changed colour), looking for interference: cases where single-task performance was worse than dual-task. Touching items that changed colour interfered with MOT, but effects varied depending on whether the item touched was a target or distractor in MOT. Touching distractors always reduced MOT performance more than touching targets. Touching targets during MOT did not interfere when there was only a single target to track but interfered more once there were two or more targets. We also measured interference based on latencies to touch items that changed colour, comparing single and dual-task conditions (touch alone, touch + track). MOT interfered with touch, increasing RT to touch items that changed colour, with latencies significantly higher when those items were distractors rather than targets. Overall, there was general interference (differences between single and dual-task performance), as might be expected if coordinating the two tasks required a common limited resource such as general attention or working memory. However, there was also differential interference that varied based on whether the touched item was a target or distractor in MOT. This differential interference suggests the specific mechanisms used in MOT may also play a role in visually guided touch.