Have you ever seen one of those visual illusions? Dogs are susceptible to visual illusions, too, just in a different way. Two illusory displays that consistently fool humans are the Ebbinghaus-Titchener & Delboeuf illusions. The Ebbinghaus-Titchener illusion presents two equally sized circles – one surrounded by small circles, and one surrounded by large circles. Humans will perceive the target circle surrounded by the smaller circles as larger. The Delboeuf illusion also presents two equally sized circles, but one is surrounded by a close ring, while the other is surrounded by a more distant ring. Here, the circle with the closer ring is perceived by humans to be bigger than the other. Most interestingly, these illusions persist in humans even when we know about them!
In order to discover how dogs perceive these perceptual illusions, researchers at La Trobe University in Bendigo, Australia trained dogs to select the larger of two target circles presented on screens. After being trained, they were then presented with three illusions: classic Ebbinghaus-Titchener illusion, illusory contour Ebbinghaus-Titchener illusion, and the Delboeuf illusion. Examples are available below, in the aforementioned order.
Dogs seemed to be susceptible to both forms of the Ebbinghaus-Titchener illusions, but not the Delboeuf illusion. However, the dogs were susceptible by thinking the circle surrounded by the large circles was bigger! The authors attributed this to a cognitive difference in how humans and dogs perceive images like these – with the dogs perceptually rescaling the target circle to be more like the surrounding circles. I wonder how many other aspects of life these perceptual differences effect? Do dogs see the world the same way we do?
Source: Byosiere, S., Feng, L. C., Woodhead, J. K., Rutter, N. J., Chouinard, P. A., Howell, T. J. & Bennett, P. C. (2017). Visual perception in domestic dogs: susceptibility to the Ebbinghaus-Titchener and Delboeuf illusions. Animal Cognition, 20, 435-448. DOI 10.1007/s10071-016-1067-1