Abstract
Attention allows for selective processing of information from the visual field. Studies of this selection process often investigate how attention can be focused on specific spatial regions. Attention, however, can also be focused on spatially invariant properties of the visual world, such as objects or features (e.g., orientation). Although object- and feature-based attention have often been viewed as distinct mechanisms, some functional relationships between the two have been found. For example, features comprising an object have been shown to be processed during object selective attention. It is, however, unclear whether feature- and object-based attention interact, or if they function independently. To address this issue, we simultaneously manipulated both object- and feature-based attention. We presented subjects with two objects, similar to Egly et al. (1994), and had them: 1) attend to one corner of one object and 2) monitor that corner for the appearance of a predetermined feature (a line segment of a specific orientation). On certain key trials, a second line segment, either congruent or incongruent with the attended feature, appeared either within, or outside, the attended object, and subjects were asked to detect this line segment as quickly as possible. As expected, both an object-based (faster detection responses for lines at attended objects) and a feature-based (faster responses for congruent lines) effects were observed. Importantly, however, these two effects did not interact. Rather, the facilitatory effects of object- and feature-based attention were additive. This finding suggests that these two attentional systems work independently in determining what portions of the visual field are selected for deeper processing.