Exogenous/Endogenous Control of Space-based/ Object-based Attention: Four Types of Visual Selection?

Attention can be directed to an object or to a location, and in a bottom-up or in a top-down fashion. The two dimensions of visual attention have elicited separate lines of research that bypassed the possibility of interactions. In the present paper, the relation between the two dimensions is explored from the initial assumption that they refer to independent aspects. If so, four types of visual selection should appear: exogenous/endogenous control of space-based/object-based attention. Examples of three of the four types are readily found in the literature, but expecting an object does not seem to affect visual selection. Therefore, endogenous control of object-based attention may not be possible, suggesting that the two dimensions of visual attention are interdependent and require a more integrative theoretical framework. However, research to date may not have provided adequate tests to observe benefits from expecting objects. Three issues remain open: the representation from which object-based selection takes place, the conditions under which object-based selection appears, and the extent of relative location expectation. It is argued that these issues call for experiments that could provide examples of endogenous control of object-based attention. Suggestions are made how to address these three issues empirically.