Evidence of a Contrast Induction Field for Peripherally Viewed Motion Stimuli

摘要

Illusions have been leveraged to reveal the mechanisms of perception since at least the time of the Gestalt psychologists of the early 1920's. Here, we characterize a new motion illusion that, to the best of our knowledge, has never been reported in the literature and is not explainable by known mechanisms. In this illusion, a peripherally viewed black square translates across a gray background. The translating square induces a field of dark areas above and below it and in the trailing tail, but not in front of it. This field of darkness vanishes when viewing the square foveally. We characterize the strength and spatial extent of the field by flashing a small probe dot at various positions around the square and having subjects perform a luminance increment detection task on the dot while fixating on a static peripheral target. We measure luminance increment detection thresholds using the method of constant stimuli in a two-interval forced-choice task. Weber's law dictates that luminance increment detection thresholds increase with increasing background intensity. Consistent with this, we find that the probe dot has lower increment detection thresholds in regions around the square perceived to be darker than it does in the regions perceived to be lighter, even though the backgrounds are physically the same. Thus, the illusory dark regions induce real differences in luminance detection thresholds around the square. We discuss potential mechanisms to explain this phenomenon.