Grouped locations and object-based attention: Comment on Egly, Driver, and Rafal (1994).

Abstract

Recently, R. Egly, J. Driver, and R. D. Rafal (1994) provided evidence for an object-based component of visual orienting in a simple cued reaction time task. However, the effects of objects on visual attention can be due to selection from either of two very different types of representations: (a) a truly object-based representation that codes for object structure or (b) a grouped array representation that codes for groups of spatial locations. Are Egly et al.'s results due to selection from an object-based representation or from a grouped array representation? This question was addressed by using a variant of Egly et al.'s task. The findings replicated those of Egly et al. and demonstrated that the selection in this task is mediated through a grouped array representation. The implications of these results for studies of attentional selection are discussed. In the past, the study of attentional selection has primarily focused on how visual attention selects stimuli on the basis of spatial location in the visual field. However, in recent years there has been an increase in the study of how visual attention selects stimuli on the basis of shape or structure. The former approaches have come to be known as spatial or location-based models of attention, and the latter have come to be known as object-based models of attention. (The literature concerning these two types of selection is quite large and continually growing, so it will not be reviewed here. The reader is referred to the following for reviews and characteristic positions: Duncan, 1984; Egly, Driver, & Rafal, 1994; Eriksen & Eriksen, 1974; Kramer & Jacobson, 1991; Posner, 1980; Posner, Snyder, & Davidson, 1980; Vecera & Farah, 1994) Egly, Driver, and Rafal (1994) used a clever procedure that was reported to show both location-based and objectbased components of visual selection in normal subjects as well as differential impairments in these attentional components in parietal-dama ged patients. The results from the normal subjects are of primary interest here. Subjects were shown two rectangles that appeared either above and below fixation or to the left and right of fixation. One of the corners was cued by brightening, and a target followed. Subjects made a simple reaction time (RT) response to the onset of the target, a procedure similar to Posner's classic spatial cuing paradigm (see Posner