Effect of Shape on the Magnitude of the Delboeuf Illusion

Three experiments to discuss the applicability of the contour attraction and the parallel attraction to different shapes in the Delboeuf illusion. The contour attraction suggests that the contours of the test figure and the inducer have an effect of interattraction in the Delboeuf illusion, and the parallel attraction suggests that the attraction between non-intersecting contours was maximal when they were parallel. In Experiment 1, the shape of the test figures and the inducers changed simultaneously and formed parallel lines. In Experiment 2, the test figures remained circles while the inducers changed shape. Experiment 3 was identical to Experiment 2 except that the areas of the inducers remained equal. The results demonstrated that the illusion is influenced by shape. Importantly, the effect of shape on the magnitude of the Delboeuf illusion is based on the contour attraction and the parallel attraction. Configurations with circles or shapes more similar to a circle were related more to the contour attraction, whereas shapes that were dissimilar to a circle were related more to the parallel attraction. We suggest that the contour attraction may be a circular modality of the parallel attraction.

Illusory size perception with stimuli from animal experiments of surround modulation

Visual illusions have long been studied because the illusory effect they induce is believed to tell us something important on how the visual system processes visual information. Here, we modified a classic visual illusion, the Delboeuf illusion, so that it resembled a type of stimulus commonly used in experiments investigating surround modulation. We then performed a small set of psychophysical experiments in order to determine if the classical Delboeuf illusion effect, i.e. a change in the perceived size of an object, could be observed in these altered stimuli. In four conditions, we created stimuli that either had a high or low frequency surround in addition to being presented with a proximal thin surround or a distal thick surround. We found a significant difference in perceived object size for all four conditions compared to control indicating the presence of an illusion, and we discuss these findings in relation to existing literature from electrophysiological animal studies.