Perceptual grouping leads to objecthood effects in the Ebbinghaus illusion

Age-related changes in the susceptibility to visual illusions of size

As the global population ages, understanding of the effect of aging on visual perception is of growing importance. This study investigates age-related changes in adulthood along size perception through the lens of three visual illusions: the Ponzo, Ebbinghaus, and Height-width illusions. Utilizing the Bayesian conceptualization of the aging brain, which posits increased reliance on prior knowledge with age, we explored potential differences in the susceptibility to visual illusions across different age groups in adults (ages 20-85 years). To this end, we used the BTPI (Ben-Gurion University Test for Perceptual Illusions), an online validated battery of visual illusions developed in our lab. The findings revealed distinct patterns of age-related changes for each of the illusions, challenging the idea of a generalized increase in reliance on prior knowledge with age. Specifically, we observed a systematic reduction in susceptibility to the Ebbinghaus illusion with age, while susceptibility to the Height-width illusion increased with age. As for the Ponzo illusion, there were no significant changes with age. These results underscore the complexity of age-related changes in visual perception and converge with previous findings to support the idea that different visual illusions of size are mediated by distinct perceptual mechanisms.

Effects of cortical distance on the Ebbinghaus and Delboeuf illusions

The Ebbinghaus and Delboeuf illusions affect the perceived size of a target circle depending on the size and proximity of circular inducers or a ring. Converging evidence suggests that these illusions are driven by interactions between contours mediated by their cortical distance in primary visual cortex. We tested the effect of cortical distance on these illusions using two methods: First, we manipulated retinal distance between target and inducers in a two-interval forced choice design, finding that targets appeared larger with a closer surround. Next, we predicted that targets presented peripherally should appear larger due to cortical magnification. Hence, we tested the illusion strength when positioning the stimuli at various eccentricities, with results supporting this hypothesis. We calculated estimated cortical distances between illusion elements in each experiment and used these estimates to compare the relationship between cortical distance and illusion strength across our experiments. In a final experiment, we modified the Delboeuf illusion to test whether the influence of the inducers/annuli in this illusion is influenced by an inhibitory surround. We found evidence that an additional outer ring makes targets appear smaller compared to a single-ring condition, suggesting that near and distal contours have antagonistic effects on perceived target size.

The competition between grouping cues can be resolved under inattention

We investigated whether attention is required for the resolution of the competition between conflicting grouping cues. Participants performed a demanding change-detection task on a small matrix presented on a backdrop composed of two organizations that could change or stay the same between two consecutive displays independently from changes in the target. We hypothesized that if the competition between the backdrop organizations can be resolved without attention, congruency effects should emerge between changes in the target and changes in the organization that won the competition, but not for the other organization. Three trial types were examined: no-conflict trials, where the two grouping cues formed the same organization (e.g., columns by proximity and by color similarity); conflict trials, where the two cues formed conflicting organizations (e.g., columns by proximity and rows by color similarity); and mixed trials, where one backdrop display depicted no conflict while the other depicted conflicting organizations. Congruency effects were elicited by one organization (Experiment 1-proximity, Experiment 2-common region) but not by the other (color similarity, Experiments 1-2), in the no-conflict and mixed trials, suggesting that if one display in a trial was well organized it facilitated the resolution of the competition in the other display. However, when resolving the competition was required for both displays within a trial, it was not accomplished without attention. Thus, this study shows novel results revealing some of the conditions in which the competition between grouping cues can be resolved without attention.