Effects of a coactor's focus of attention on task performance.

Coactors take into account certain aspects of each other's tasks even when this is not required to perform their own task. The present experiments investigated whether the way a coactor allocates attention affects one's own attentional relation to stimuli that are attended jointly (Experiment 1), individually (Experiment 2), or in parallel (Experiments 3 and 4). Pairs of participants sitting next to each other performed a two-choice Navon task, responding to the identity of letters. Participants' tasks either required the same focus of attention (e.g., both attending to local stimulus features) or different foci of attention (e.g., one attending to local and the other to global features). Results revealed a significant slow-down of responses when participants focused on different features, suggesting that the coactor's attentional focus induced a conflict that affected the selection of one's own focus. This effect disappeared when no other person was present, and when mutual visual access to each other's stimuli was disrupted, but did not depend on a triangular relationship between participants and stimuli. Our findings extend previous research on joint attention and task corepresentation in revealing that representations of a coactor's task can include a specification of her focus of attention.