Object-based attention shifts are driven by target location, not object placement

Object-based attention (OBA) enhances processing within an attended object. We previously found that attention shifts that crossed the visual field meridians were faster horizontally than vertically, which we named a Shift Direction Anisotropy (SDA). We aimed to determine whether the SDA depends upon attention shift meridian crossings of object boundaries, target locations, or both. Participants viewed an ‘L’-shaped object and responded to a target at the cued vertex location (valid) or at non-cued object locations offset horizontally (invalid-horizontal) or vertically (invalid-vertical). In Experiment 1, object boundaries and target locations were positioned either crossing or not crossing the meridians. In Experiments 2A and 2B, object boundaries were held constant (always crossing or never crossing the meridians, respectively) while target locations were manipulated (randomly crossing or non-crossing). In Experiments 3A and 3B, target locations were held constant while object boundaries were manipulated. In Experiment 4, the object was removed to determine whether object-based or space-based attentional resources were being deployed. The SDA emerged only when target locations necessitated shifts that crossed the meridians, regardless of object placement, demonstrating that the SDA is driven by target location relative to the meridians and that OBA processes prioritize specific target locations within an object.