Abstract
The perception of an object's features can often be biased by the object's immediate surroundings, leading to many perceptual illusions. In contrast, the presence of nearby, static objects often enhances the perceived spatial location of another object. Here we present a new type of visual illusion in which the presence of a static object (the attractor) alters another object's perceived location. Participants localized the edge of a briefly presented and masked target object (e.g., an outline square or a centrally presented line). Localization was accurate when the masked target was presented in isolation. However, when another nearby object (e.g., a face) was presented at the same time as the target, localization deviated toward the nearby object. This “visual attractor illusion” (VAI) was found across different attractor types and across different colors of targets and masks. The VAI is a relatively unique phenomenon that can be distinguished from other mislocalization effects such as foveal bias, the flash-lag effect or the landmark effect. Furthermore, the VAI is a relatively high-level effect that appears to be modulated by attention: It was stronger when the attractor object was task-relevant rather than task-irrelevant, and diminished as the experiment progressed. 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 discuss two possible mechanisms: 1) the distortion of perceptual space by the brief appearance of an object, which draws in the perceived location of a neighboring object; 2) localization of a masked target may be weighted towards the position of a concurrently presented visual transient. The VAI may provide a unique example of a grouping-and-assimilation effect in the spatial domain.
Grant-In-Aid University of Minnesota.