Abstract
The contribution of object based representations to attentional guidance has been focused almost exclusively within the framework of top-down attentional control, and little is known regarding its contribution to bottom-up, or stimulus driven, attentional control. In our recent behavioral investigation, we demonstrated that attentional capture is in fact object-based, and that the extent to which objects guide attentional capture is modulated by the involvement of top-down attentional orienting. In the present set of two fMRI experiments, we investigated the neural mechanism of object-based attentional capture, namely the involvement of SPL and TPJ in contingent capture (with top-down involvement) and pure capture (bottom-up involvement). Participants viewed a central rapid serial visual presentation (RSVP) stream in which a target letter was either defined by a specific color (Experiment 1, contingent capture) or could be one of four random colors (Experiment 2, singleton capture). The RSVP stream was superimposed onto a set of three objects (a cross like configuration). On critical trials, a task-irrelevant color singleton and three neutral distractors appeared in the periphery. On half of the trials the colored singleton appeared on the same object as the central target, and on the different object on the other half. We observed capture related activations in the SPL/precuneus and TPJ regions for the contingent capture, and TPJ activation exclusively for the singleton capture. Additionally, these capture related activations were modulated by whether the singleton appeared on the same- or different object (i.e, object-based effect). Furthermore, with the use of retinotopic mapping, the effects of such object-related attentional capture were examined in the early visual cortex. These results suggest that object-based representations guide bottom-up as well as top-down attentional orienting, as well as provide further constraints on the mechanisms of attentional guidance and of object-based selection.