Sometimes more (overlap) is better! Action plan overlap impacts the interference between visually-guided touch and multiple-object tracking (MOT)

When two tasks are performed simultaneously their action plans can overlap with one another. Past findings suggest that the overlap can either improve or degrade performance, depending on the relatedness of the required actions (e.g., Fournier et al. 2015). In this study we assessed the impact of overlapping action plans in a multiple-object tracking (MOT) task. Participants tracked 1-4 MOT targets while also touching moving items in MOT that changed colour. To determine the effects of action plan overlap between the MOT and touch task, we manipulated the way that participants reported the identity of the targets at the end of the trial (untimed). In the touch task participants always used the index finger of their dominant hand. To report the targets participants either typed in the letters corresponding to the targets with their non-dominant hand (minimal overlap) or touched MOT targets with the index finger of their dominant hand (maximal overlap). Target report method had no effect on single-task MOT performance. However, when participants had to touch moving items that changed colour during tracking (dual-task), MOT performance was significantly worse when overlap was minimized. It also took participants longer to touch moving items that changed colour - even though target report occurred 7-8 seconds later. Nonetheless, MOT performance was always better and touch latencies lower when the touched items were targets as compared to distractors in MOT; report technique had no effect. This shows a dissociation between the effects of attentional selection in MOT and overlapping action plans.