Spreading and Shifting of Attention: The Role of Object.

Object-based attention (OBA) is a selective attention mechanism that suggests that attention selects an object as a processing unit. This mechanism has been widely studied using the double-rectangle paradigm (Egly et al.), with shorter reaction times (RTs) in the within-object than in the between-object conditions as the OBA effect. However, this paradigm could not distinguish whether this OBA effect reflects a within-object benefit or a between-object cost. To address this issue, the present study employed the single-rectangle paradigm to disentangle the processes of spreading and shifting attention within an object, within space, and across an object's boundary. In Experiments 1 and 2, attention was encouraged to spread by using a two-target comparison task. The results revealed that spreading attention within an object is faster than within space, but the object boundary can impede this spreading. In Experiment 3, a detection task was used to encourage attentional shifts. Results showed that shifting attention across an object boundary incurs a cost, whereas shifting within an object provides no advantage over shifting within space. These findings, largely replicated with briefly disappeared objects, suggest that the OBA effect involves both a within-object benefit and a between-object cost, providing insights into how object influences attentional shifting and spreading.