Abstract
This study investigated the nature of the spatial computations that underlie the symbolic control of visual attention. At issue is the specificity of the spatial information that is conveyed by directional symbols such as spatial words (ABOVE, BELOW, LEFT and RIGHT) and corresponding arrows. Consider a right-pointing arrow that appears at fixation and is intended to direct attention to a location in the periphery. Abundant evidence has been interpreted to suggest that such cues can direct attention to specific locations based on findings showing that RTs are faster when a subsequent target appears at a location in the cued direction relative to when it appears at an uncued location in the opposite or orthogonal direction. However, previous studies have typically presented targets at only a single location along each cued direction, making it difficult to ascertain the specificity of the spatial information that was conveyed by the cue. Accordingly, the present study presented targets at one of three possible locations in each direction. Three different spatial cues were compared: word cues, arrow cues, and onset cues. The target always appeared at one of the three locations along the cued direction with the constraint that it appeared at one of the three locations 80% of the time and at the other two locations 20% of the time. Observers were informed of these contingencies and they were instructed to shift their attention to the most probable location. The specificity of the spatial information conveyed by the three cues was estimated by the magnitude of the cuing effect (uncued RT - cued RT) observed along each cued direction. The results suggested that the word cues and arrow cues conveyed less specific spatial information than the onset cues, thus revealing weaknesses in the computation of metric spatial information necessary for directing attention to specific locations.