Development of the hippocampus and the ability to perceptually integrate images drive the emergence of visual illusion susceptibility in childhood
Keela Thomson1, Samantha Gualtieri1, Kay Otsubo1, Morgan Barense1, Asaf Gilboa1,2, Amy Finn1; 1University of Toronto, 2Rotman Research Institute at Baycrest
Young children are less susceptible to the Ebbinghaus visual illusion—in which misleading contextual information distorts an object’s apparent size—than older children and adults (Doherty at al., 2010). We investigated the possibility that this is due to changes in the ability to perform perceptual integration across development (Kovacs, 2000) due to ongoing development of the hippocampus (Barense et al., 2010). We hypothesized that young children do not integrate the misleading image context, preventing it from affecting their size perceptions. If so, physically integrating the image components for viewers should allow children to “see” the illusion. Children aged 4-10 (n=93) and adults (n=30) viewed the Ebbinghaus, Sander, and Vertical-Horizontal illusions. These illusions differ in whether target items and surrounding context are visually integrated: the Ebbinghaus illusion is unintegrated (target and context do not touch) and the Sander and Vertical-Horizontal illusions are integrated. Consistent with prior work, younger children experienced the (unintegrated) Ebbinghaus illusion less than older children. In contrast, children of all ages were equally susceptible to the (integrated) Sander and Vertical-Horizontal illusions. These findings indicate that the ability to integrate visual context drives the developmental emergence of illusion susceptibility. We further explored the role of hippocampal development by investigating categorical perception, a hallmark of hippocampally-mediated processes in which continuous perceptual differences are binarized (experienced as a sudden shift). We examined the degree to which participants’ responses varied sigmoidally (as expected in categorical perception) versus linearly. Young participants were less categorical, suggesting developmental change in the role of the hippocampus.
Topic Area: PERCEPTION & ACTION: Vision
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