The strength of the Shepard illusion in children coincides with age and cognitive skills but not perceptual abilities

We examined how the strength of the Shepard illusion develops with age in typically developing children. To this end, we recruited children between the ages of 6 and 14 years and quantified the degree to which they experienced the illusion. The strength of the illusion increased with age – reaching adult levels by 11.5 years. We also measured abilities in size and shape discrimination, receptive language, and abstract reasoning to determine if changes in illusion strength were also associated with these factors. Abilities in size and shape matching increased with age but did not correlate with the strength of the Shepard illusion. Receptive language and abstract reasoning increased with age and correlated with the strength of the Shepard illusion. However, a multiple regression analysis revealed that they did not contribute beyond their shared variance with age. Based on these findings, we propose that the illusion has a strong acquired component to it and requires the maturation of high-level processes before it is experienced to adult levels at preadolescence.