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When 3D animated balls on a computer screen defy certain laws of physics, dogs act in a way that suggests they feel like their eyes are deceiving them.

Pet dogs stare for longer and their pupils widen if virtual balls start rolling on their own rather than being set in motion by a collision with another ball. This suggests that the animals are surprised that the balls didn’t move the way they had expected them to, says at the University of Veterinary Medicine, Vienna.

“This is the starting point for learning,” says Völter. “You have expectations about the environment – regularities in your environment that are connected to physics – and then something happens that doesn’t fit. And now you pay attention. And now you try to see what’s going on.”

Human infants, starting at around 6 months old, and chimpanzees stare longer during these kinds of “violation of expectation” tests concerning their physical environments, he says.

Studies in humans have also shown that pupils dilate more in reaction to increased mental efforts, like calculating, or stronger emotions such as excitement or surprise – known as the psychosensory pupil response. And in dogs has hinted that they dilate their pupils more when looking at angry human faces compared with happy human faces.

Völter and his colleague , also at the University of Veterinary Medicine, decided to see how dogs viewed animated rolling balls that didn’t always follow basic laws of contact physics. They trained 14 adult pet dogs – mainly border collies, Labrador retrievers and mixed breeds – to place their heads on a chinrest in front of a computer screen and eye-tracking equipment. Then they showed the animals brief videos, in random order, of colourful 3D balls in motion.

In one video, a ball rolls towards a second, stationary ball and then runs into it. The first ball stops and the second one starts moving – just as Newton’s laws of motion describe. In another video, however, the first ball rolls toward the second ball, but stops suddenly before reaching it. And then, the second ball suddenly starts rolling away by itself – contrary to basic physical principles.

Like human infants and chimpanzees, dogs fixed their eyes longer on the balls that didn’t move in a logical way, Völter says. Even more convincing, though, was the reaction in their pupils: they consistently viewed the “wrong” scenarios with more enlarged pupils, suggesting this was contrary to their expectations.

This doesn’t mean dogs necessarily understand physics, with its complex calculations, says Völter. But it does suggest that dogs have an implicit understanding of their physical environment.

“This is sort of [an] intuitive understanding expectation,” says Völter. “But that’s also the case for humans, right? The infant at 7 months of age has expectations about the environment and detects if these expectations are violated. I think they build up on these expectations, and build a richer understanding of their environment based on these expectations.”

How dogs use such unexpected information is yet to be investigated, Völter says.

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