Psychologists use visual illusions all the time to study the shortcuts the human brain uses to extract information about the world, explains Philippe Chouinard, an expert on illusions… Usually, shortcuts are a reliable way for brains to obtain information rapidly, he says, but sometimes they’ll result in a mistake—causing us to “see” things that aren’t there, or to perceive a difference in size between two identical objects, for example. Identifying when and how mistakes such as these arise can offer clues as to how cognition works, in humans or other animals, such as domestic dogs.
The team used various versions of the Ebbinghaus-Titchener illusion, in which two same-sized circles appear to humans to be different sizes due to arrangement of other circles around them. Each dog had been trained… to select whichever of the two center circles it perceived to be larger by tapping its nose to that part of the screen.
To [researcher Sarah] Byosiere’s excitement, the data revealed that dogs did indeed show susceptibility to the Ebbinghaus-Titchener illusion… But rather than falling for the trick as humans do, picking the circle surrounded by smaller circles as being larger, the dogs did the exact opposite.
The findings were a striking illustration of how little science knows about canine perception, even though humans have for millennia had close relationships with dogs, says Byosiere.