Sheep, llamas and goats fall for optical illusions too

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People around the world keep goats, sheep, llamas and other ungulates as pets and livestock. Yet very little is known about how these animals think and perceive the world.

Alina Schaffer is on a mission to get inside these animals’ heads. She works at the University of Leipzig in Germany. Recently, she and her colleagues tested whether ungulates fall for optical illusions like humans do. If so, that would suggest these animals have similar neural wiring for vision as our own.

How do you see the world through the eyes of a llama or a goat? With a clever experimental setup and a lot of tasty treats.

The team shared their work in Animal Cognition on May 24.

A graphic tale" with animals drawn around the letters

A white llama chows down on a mouthful of hay, with sound labels indicating “munch munch munch munch.”

At a glance, which of these two orange lines looks longer? Image: There are two vertical orange lines side by side. The left vertical orange line has two inward pointing arrows attached to its top and bottom ends. The right vertical orange line has two outward pointing arrows attached to its top and bottom ends. Text (below image): They’re actually the same length! But if you picked the line on the left, you’re not alone. Many people fall for this visual trick, known as the Muller-Lyer illusion.

Let’s try another one. Which of these two orange circles looks bigger? Image: There are two orange circles side by side. The orange circle on the left is surrounded by a slightly larger white circle. The orange circle on the right is surrounded by a much larger white circle. Text (below image): These orange circles are the same size, too! But an effect known as the Delboeuf illusion can make the left one seem bigger than the right.

But what about animals? Can their eyes play tricks on them, too?

The team worked with 17 animals at the Leipzig Zoo in Germany. First, the researchers confirmed that the animals would generally pick a bigger snack over a smaller one. Then, they offered the animals treats arranged in the form of optical illusions.

The woman wearing the purple shirt stands in a field, holding up a piece of cardboard to show a goat. The cardboard has two carrot sticks stuck to it, as described above. The goat is thinking, “A little treat? I’ll take the large, please!” Text (below image): Animals across species picked the carrot between the inward-pointing sticks 77 percent of the time, suggesting they perceived that carrot to be bigger.

The woman wearing the purple shirt stands in a field, holding up a piece of cardboard to show a guanaco. The cardboard has two bunches of veggies stuck to it, as described above. The guanaco is thinking, “A little treat? I’ll take the large, please!” Text (below image): The animals went for treats on the smaller circle 73 percent of the time, hinting they saw that as the bigger snack. “They really perceive [these illusions] in the same way as humans," says team member Alina Schaffer. She studies ungulate cognition at the University of Leipzig.

The blonde boy in the art gallery looking at the Muller-Lyer illusion is joined by a white llama. The boy says, “Are you seeing this?” The llama says, “Dude, right?” Text (below image): “I think [people assume], ‘They’re just dumb animals without any feelings or any cognitive skills,’ but they aren’t,” Schaffer says. “They’re really intelligent…and they are maybe more similar to us than we think.”

Finding out which creatures fall for optical illusions could help pin down when and why this strange phenomenon emerged in the history of animal evolution.

J. Wendel

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