Abstract
We demonstrate a new visual illusion involving the illusory conjunction between color and shape. A bar gradually changes size as it moves horizontally. Somewhere along its trajectory, it also changes to a different color for one frame. The new color is perceptually assigned to a different sized bar at a new spatial location. This new illusion differs from the previously reported illusory conjunction of features (e.g. Treisman & Schmidt, 82) in several important ways. First, previous illusory conjunction was obtained under split-attention conditions. This new form of illusory conjunction can be obtained at the center of focal attention. Second, previous illusory conjunction usually occurred in less than 50% of trials, whereas this new form of illusory conjunction occurs in nearly 100% of trials. Third, this new form of illusory conjunction is directly perceived by the subjects, and it can be quantitatively measured by psychophysical techniques; whereas the previous illusory conjunction was usually recalled by the subjects after the trial, and the features being conjoined were of a random nature. We propose a model that predicts the amount of this illusory conjunction. It is based on the principle that the brain represents continuously changing features of an object in a fundamentally different way from abruptly changing features. This difference leads to an asynchrony in the processing of abrupt and continuous features, resulting in a misbinding between the two. We will show how this model can also account for a number of other illusions in the literature.