A Co-actor's Focus of Attention Affects Stimulus Processing and Task Performance: an ERP Study

When acting and attending together, we take each other's perceptual and intentional relations to the environment into account. The present study investigated whether people are also sensitive to a co-actor's attentional relation to jointly attended events. Two participants sat next to each other and performed a two-choice Navon task, responding to the identity of letters formed by identical (congruent) or different (incongruent) smaller letters while EEG was recorded. Crucially, participants either held 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. Amplitudes of the occipital P1 and parietal occipital P3 decreased when attentional foci differed. The amplitude of the fronto-central N2 increased when the other attended to local as compared to global features. These results suggest that representations of a co-actor's task can include a specification of his or her focus of attention. Taking into account the other's different attentional relation to stimuli likely induces a conflict at the level of task selection, impairing early allocation of attention (P1) and enhancing the need to monitor response initiation (P3).