Sixteen participants were recruited into 4 age groups (3-4, 5-6, 7-9 yrs, adults). Participants were seated in front of a touch-sensitive video display and equipped with a head-mounted eye-tracker. Each participant was instructed on the match-to-sample concept, and then completed 2 practice runs consisting of a shape or orientation discrimination task using real, complete forms (10 trials each). They were then tested with 6 different real shapes as sample stimuli and KICs for matching comparison stimuli (40 trials).

Only one of four 3-4 year-olds tested performed above 80% correct (criterion) on both practice runs and the KIC discrimination. All older participants passed criterion on the practice runs, while performance with KICs was 77% (5-6), 96% (7-9), 100% correct (adult). Interestingly, location of gaze and locus of touch (response) depended on age and stimulus type. With real forms, final gaze position and touch location were directed at the image center regardless of age. However, with KICs, children under 6 primarily looked at and touched individual contour inducing elements (pacmen), whereas older children and adults looked at and touched the center of the KIC. These results show clear developmental changes in the ability to appreciate illusory forms, and a modification of processing strategy with age and stimulus type.