Eye movements to motion-defined and luminance-defined forms

Abstract

A prominent area of inquiry in neuroscience and vision is the binding problem: how does one account for the brain integrating the different features of an object (e.g. luminance, velocity, color, and texture) when it has been shown repeatedly that separate areas of the brain code for separate features of the object. To approach this question, we characterized eye movements (more specifically, saccades) to forms defined by luminance and forms defined by motion. Luminance-defined form (LDF) is a visual stimulus that is distinguished from its background due to a difference in luminance between it and the background. Motion-defined form (MDF) is a visual stimulus created by moving components within the form in one direction and having the components of the form's background move in the opposite direction. Saccades to MDF were very similar to those of LDF, meaning saccades to both types of form were highly correlated with target location. This novel discovery demonstrates that the oculomotor system can make accurate eye movements to MDF. Secondly, it was shown that saccadic endpoints were biased in the direction of dot motion of MDF. This global illusory shift in target position caused by local motion agrees with perceptual literature (Regan, 1993). Thirdly, saccades made to MDF while the subject was told to ignore a simultaneously presented LDF were biased in the direction of the offset LDF. Results indicate that saccades and MDF will be useful tools in studying the binding problem and that there may be a hard-wired tendency to bind features to create single a "object."