Abstract
While some recent studies suggest that object-based attentional selection is driven by spatial uncertainty of target location (Shomstein & Yantis, 2002, 2004), other studies suggest that target-to-object relationship, rather than uncertainty, is the determining factor (Chen & Cave, 2006; Richard, Lee, & Vecera, 2008). In the present study we re-evaluate the contribution of spatial uncertainty to object-based effects as well as examine the interaction of uncertainty with target-to-object relationship. In a series of four experiments we manipulate uncertainty and target-to-object relationship to examine the extent to which target uncertainty contributes to object-based attention. Participants were presented with a series of single and multiple objects that contained “bites” (concavities), and were asked to perform a shape discrimination task in two conditions: (i) when target location was known in advance (certainty), and (ii) when target location was uncertain. In addition, the properties of the “bites” were manipulated, they were either interpreted as being part of the object or as having been placed on to the object. We observed object-based effects when target location was uncertain, and only if the targets were interpreted as being a part of the object. On the other hand, when target location was known in advance, or when the target shapes appeared to be independent of the object (i.e., not a part of it), object-based effects disappeared. These results re-instate the importance of location uncertainty in object-based attentional guidance, and suggest that object properties have to be task relevant if they are to influence object-based effects.