Distinct effects of target individuation and target report method in multiple-object tracking

This project examines the mechanisms underlying multiple-object tracking (MOT) and their role in visually guided action. MOT requires observers to track several identical moving targets among distractors and is widely used to study attention in dynamic visual environments. Many theories have been proposed to explain how individuals track multiple moving objects at once, though most do not address how MOT supports coordinated action. One influential account (Pylyshyn's Visual Index Theory) proposes that MOT relies on an item individuation mechanism that assigns spatial indexes to targets, allowing their locations to be accessed directly and used to guide action. In support of this theory, previous dual-task studies combining MOT with visually guided touch have revealed differential interference, whereby tracking accuracy and touch latencies depend on whether a target or a distractor is touched during tracking. However, prior work confounded this interpretation with response overlap, as participants used manual responses both during tracking and to report MOT targets. The present study extends this initial finding by manipulating the method used to report MOT targets. Participants perform MOT either alone or concurrently with a visually guided touch task in which they must touch items that change colour during tracking. Target report method varies between groups: participants report targets either by touching them or by verbally reporting letters associated with target locations. These report methods differ in motor demands while holding task structure constant. The primary objective is to determine whether differential interference persists across report methods or depends on response overlap. Secondary analyses assess the effect of report method on general dual-task interference. Results inform theoretical accounts of item individuation, attention, and action planning.