Multiple-Object Tracking and Visually Guided Touch: Dual-Task Interference Reveals Distinct Effects of Target Indexing and Target Report Method

Multiple-object tracking (MOT) involves monitoring the positions of multiple targets as they move among identical distractors. Pylyshyn proposed that the mechanisms employed to track targets in MOT are also integral to coordinated actions. In support of this, previous research demonstrates that MOT and visually guided touch interfere with one another. However, in these early studies, reporting the MOT targets at the end of the trial involved touching them, making it unclear whether interference reflected competition for a shared limited-capacity item individuation mechanism or similarity in the motor responses required by the two tasks. To address this issue, we had participants touch items that changed colour during MOT with the index finger of their dominant hand and manipulated how participants later reported MOT targets at the end of the trial. We compared performance when participants reported MOT targets by touching them with the index finger of their dominant hand with that when they identified targets verbally or by typing them in. Two findings emerged. Firstly, the target report method had an effect on the size of the difference between single- and dual-task performance (general interference). Secondly, the target report method had no effect on differential interference (the size of the dual-task performance advantage when participants touched targets rather than distractors during MOT). The dissociation between the effects of target report on general and differential interference suggest these two types of interference reflect different processes. This research has implications for those who study the formation of action plans.