[Age related size invariance in perception of illusory and fragmented contours]

We investigated invariant perception to sizes of images. Observers were schoolmates of 7-17 years and adults. Two types of stimuli were used: fragmented line drawing of common objects and discs with deleted sectors, which represented illusory Kanizsa contours when discs were in particular positions. In experiments with fragmented images, we found an improvement in image recognition with observers' age, increasing up to 13-14 years. The probability of recognition of fragmented line drawings increased significantly with decreasing stimulus size for children of 7-12 years, indicating that size invariance at recognition for fragmented line drawings was absent in these children. However, size invariance was found for observers of 13-17 years and for adults in this task. At Kanizsa illusion appearance, the ratio of the separation between discs and disc diameter was smaller when we used larger disc diameters. This ratio increased with increasing age of observers. Obtained results provide evidence for the absence of size invariance when perceiving the Kanizsa illusion in our experimental conditions.