Frames of reference for allocating attention to space: evidence from the neglect syndrome.

With respect to what frames of reference, or spatial coordinate systems, is attention allocated to locations in space? We posed this question about the spatial attention system that has been damaged in neglect patients, distinguishing among three possible types of spatial reference frame: viewer-centered, according to which locations are coded with respect to the viewer, environment-centered, according to which locations or coded with respect to the environment, and object-centered, according to which locations are coded with respect to an object. The three candidate frames of reference were decoupled from one another by rotating either the viewer or the stimulus object. Visual search performance suggested that the neglected hemifield was defined with respect to both viewer-centered and environment-centered frames of reference, but not with respect to an object-centered frame of reference. The role of objects in the allocation of attention to space, and the relation between our findings and the "two cortical visual systems" hypothesis, are discussed.