When a part of an object is cued, targets presented in other locations on the same object are detected more rapidly and accurately than are targets on other objects. Often in object-based attention experiments, cues and targets appear not only on the same object but also on the same surface. In four psychophysical experiments, we examined whether the "object" of attentional selection was the entire object or one of its surfaces. In Experiment 1, facilitation effects were found for targets on uncued, adjacent surfaces on the same object, even when the cued and uncued surfaces were oriented differently in depth. This suggests that the "object-based" benefits of attention are not restricted to individual surfaces. Experiments 2a and 2b examined the interaction of perceptual grouping and object-based attention. In both experiments, cuing benefits extended across objects when the surfaces of those objects could be grouped, but the effects were not as strong as in Experiment 1, where the surfaces belonged to the same object. The cuing effect was strengthened in Experiment 3 by connecting the cued and target surfaces with an intermediate surface, making them appear to all belong to the same object. Together, the experiments suggest that the objects of attention do not necessarily map onto discrete physical objects defined by bounded surfaces. Instead, attentional selection can be allocated to perceptual groups of surfaces and objects in the same way as it can to a location or to groups of features that define a single object.
Keywords: Attention spreading; Cue facilitation; Object-based attention.