Posted by Dave on May 12, 2010 | 1 Comment
The Kanizsa Illusion is one of the best-known and simplest visual phenomena:
Most adults readily see not only the three “pac-men,” but also the triangle formed by their “mouths.” This effect can be used to create virtual rectangles, stars, and other more complicated shapes. What’s less clear is at what age children are first able to see the illusion. Some research suggests that infants are able to perceive it, but other studies find that kids as old as five or six still have difficulty recognizing the shapes suggested by the pac-men.
So a team led by Kimberly Feltner developed a test that could be administered to kids as young as three years old. They trained children ranging from age three to nine, as well as adults, in three phases: comparing shapes, comparing orientation, and finally comparing real shapes to shapes suggested by Kanizswa contours. In each case, they first saw a model shape, then chose between two choices to identify matching shapes, presented as real shapes or Kanizswa illusions depending on the training phase.
Every age group could complete the first two tasks at 80 percent accuracy, but children age three to four had difficulty with the Kanizswa task, only getting about 70 percent correct. This is still better than random guessing, so in some senses these young kids can do the task, but the researchers suspected that younger kids were taking a different approach to the problem.
Using eye tracking software, the researchers analyzed where the kids (and adults) were pointing. Here are the results:
When looking at real shapes, both adults and children looked mostly at the middle and edges of the shapes. But when looking the shapes presented in the form of Kanizsa illusions, younger children looked primarily at the corners of the pac-men, suggesting they may have been perceiving the illusion in a different way from the adults.
Since selections were made with a touch screen, the researchers also tracked where the kids were pointing. Pointing matched looking behavior — even when the youngest children selected the correct Kanizsa figure, they were significantly more likely than adults to point at the corners or pac-men rather than the center of the shapes. Three- and four-year-olds actually tried to touch all the corners of the Kanizsa figure simultaneously. While it’s unclear from this experiment exactly what these young children were perceiving, it seems likely that they were processing the Kanizsa figures differently from older kids and adults.
Could they literally not be seeing an illusion that’s dramatic and clear for most adults? It’s hard to tell from this study. The fact that they look at the corners rather than the center of the shape does seem to indicate that they perceive it differently. It may be that the ability to perceive an illusion like this is acquired gradually.
Feltner, K., Mayar, K., Adolph, K.E., & Kiorpes, L. (2010). Kanizsa illusory contour perception in children: A novel approach using eye-tracking. Poster presented at Vision Sciences Society Meeting, Naples, FL.