The visual attractor illusion.

In many visual illusions, the perceived features of an object such as its size or orientation are influenced by nearby objects. In contrast, the presence of nearby, static objects often enhances the perceived spatial location of another object. Here we present a type of visual illusion in which the presence of a static object alters another object's perceived location. Participants localized the edge of a briefly presented and masked target object. Localization was accurate when the masked target was presented in isolation. However, when another nearby object was presented at the same time as the target, localization deviated toward the nearby object (the "attractor"). This "visual attractor illusion" was stronger when the attractor object was task-relevant rather than irrelevant and diminished as the experiment progressed, suggesting that it was modulated by attention. Visual transients also play an important role in the illusion, which depends on the sudden onset of the attractor object and backward masking of the target. We suggest that the brief appearance of an object (the attractor) distorts perceptual space and draws in the perceived location of a neighboring object. Alternatively, localization of a masked target may be weighted toward the position of a concurrently presented visual transient.