Researchers find chimps, like people, can be fooled into overeating

(Phys.org) —Many of us can think of a time when we've eaten more food than we wanted, especially around the holidays.

Now, research at Georgia State University shows chimpanzees also suffer from this common human problem – their eyes can fool their stomachs.

Over-eating sometimes is linked to our perceptual system, which can trick us into thinking there is more (or less) food than there really is. A slice of cake on a small dinner plate can look larger than the exact same piece of cake on a larger plate, for example.

Research with humans has shown equal food portions were misperceived on the basis of the dinner plate on which they were presented, leading to over-serving and over-consumption from large plates and under-serving and under-consumption from small plates.

Researchers Audrey Parrish and Michael Beran have found chimpanzees also misperceive food amounts based on plate size.

Chimpanzees from Georgia State's Language Research Center participated in a study in which they chose between two amounts of a highly preferred food, presented on either identical or different-sized plates. The chimpanzees were very good at selecting the larger food portion when both choices were presented on the same-sized plates.

However, they made the same mistakes people sometimes make when the food portions were presented on different-sized plates (a small plate versus a large plate). When equal portions were presented on different-sized plates, the chimpanzees preferred the small plate to the large plate even though they both contained the same amount of food.

And sometimes, when a smaller food portion was on a small plate and a larger portion was on a large plate, the chimpanzees chose the smaller amount, presumably because it looked larger when it filled up a greater portion of the plate it sat on.

These results demonstrate people share a common visual illusion with, at minimum, our closest living relative, the chimpanzee.

"Here, we see similar behaviors from chimpanzees as we see with humans," Parrish said. "But chimpanzees misperceive food sizes despite having limited cultural norms or experiences with dinnerware compared to humans."

She further noted that these results "suggest that it might be harder to convince the stomach to ignore the eyes than we would hope to be true, as this illusion seems to occur across species."

The research findings have been published in a paper in the journal Animal Cognition titled "When less is more: Like humans, chimpanzees (Pan troglodytes) misperceive food amounts based on plate size."