Abstract
Background: Studies of flanker interference (FI) have suggested that spatial attention operates as a spotlight or gradient within the visual field, selecting stimuli within the attended region (e.g., Eriksen & Hoffman, 1973). In contrast, recent data suggest that it is difficult to divide attention between multiple objects that are near one another in the visual field, an effect that has been called localized attentional interference (LAI) and has been attributed to competition between visual objects for the control of neural resources (e.g., McCarley, et al, 2004; Mounts & Gavett, 2004). The present experiments examined the relationship between FI and LAI. Method: Observers made speeded identity judgments of a colored target letter embedded in an array of gray filler letters. A response-compatible or -incompatible flanker letter of a nontarget color appeared at varying distances from the target. RTs for target judgments were analyzed as a function of target-flanker separation and compatibility. Results and conclusions: Data gave evidence of LAI together with spatially graded FI, with mean RTs and flanker compatibility effects both decreasing as target-flanker separation increased. A second experiment found that both forms of interference were reduced when the target location was spatially cued prior to imperative display onset, confirming that both effects were attentional. Results suggest a model in which distance from the focus of spatial attention modulates the relative strength of stimulus objects competing for visual representation.