Peacocks, Eye Tracking, and the Brains Behind Decisions

How do male peacocks size up their competition? Not by looking at the brightly colored tail feathers and upper eyespots for which these birds are known, but instead by focusing on their lower feathers and legs. The birds also pay more attention when their competitors shake their tails and move rather than when they are sitting still.

That’s according to new research from Penn Integrates Knowledge professor Michael Platt and Jessica Yorzinski, a former postdoctoral fellow of Platt’s and now an assistant professor at Texas A&M University. They published their findings in the Journal of Experimental Biology.

This is the latest work in a quest to better gauge how animals, such as lemurs, monkeys, and even humans, acquire information about the surrounding world, combine that knowledge with internal decision-making mechanisms, and respond accordingly.

“One of the ways that we go about understanding how we make decisions is to measure precisely what people and other animals use in terms of visual information to guide subsequent decisions,” Platt explains. “So we utilize what are now known as eye-tracking goggles.”

For humans, that essentially equates to a pair of funky-looking eyeglasses. A camera at its outside-facing midpoint offers the view of what the person wearing them sees. On the inside sit an infrared camera and an infrared illuminator, the latter of which shines a light that disappears into the pupil and gets reflected in the cornea’s layers. A computer then decodes, based on the reflective angles, where the eye is looking. 

“It’s a nifty piece of engineering, but it’s basically just geometry,” Platt says.

It’s not quite as simple for animals, since they typically don’t have a head structure on which such headgear could sit. So for this experiment, Platt and Yorzinski employed a different model.

Using moldable plastic, they created a hat shaped to each peacock’s head that held a camera, which they strapped on like a bike helmet. A tiny, lightweight backpack held the transmitter. Because the birds have laterally placed eyes (on the sides of their head, looking out, to detect predatory action in either direction), the researchers covered one with a patch. This acted as a control to hone in on the movements of the other. 

“They looked a little bit like Patrick Stewart in ‘Star Trek’ when he had been taken over by the Borg and he had this headgear on, with this eyepiece looking out,” Platt says. “They were the Borg peahens.”

For 14 male adult peacocks, species Pavo cristatus, the researchers used these eye-tracking devices during mating season to watch where each animal looked when placed in an enclosure with one rival and two females for up to 90 minutes. Each focal male—the one wearing the gear—participated in up to four trials, for a total of 28.

Sorting through 230 clips, Platt and Yorzinski found that these males spent more than a third of their time looking at displaying rivals, particularly at the feathers nearest to the feet. Similarly, it’s where females focus attention with a displaying male.

“Neither male nor female peacocks spend much time looking at all the plumage, which really raises a lot of questions about why in the world male peacocks would invest so much energy in its development,” Platt says. “We think it probably has something to do with signaling from a distance in dense vegetation, and also potentially during competition between males.”

It’s only been in the past decade that animals like peacocks could participate in such research, thanks to technology improvements leading to lighter equipment. (Previously, heavy-duty, non-portable cameras required subjects to sit still, in a lab, with their heads in a chin rest.) Since the technology has become more accessible, researchers have also learned a great deal about information-processing in the animal kingdom, particularly in regard to humans and closely related cousins.

Platt cites the example of ring-tailed lemurs he studied at Duke University. By training these primates to wear headgear cameras, he and colleagues could demonstrate the animals’ social characteristics, noting that unless the lemurs were actively searching for food or climbing a tree, they were typically looking at other lemurs. The researchers also discovered the animals followed one another’s gaze, something that was, until recently, considered a uniquely human behavior.

“If I see you turn and look over there, I’m going to turn and look in the same direction. This is gaze following. It is thought to be a precursor developmentally for theory of mind, which is how we understand the mental states of others,” Platt explains. “It’s a behavior that falls apart during the first two years of life in kids who develop autism, and it seems to presage other problems, social problems, problems in language learning, probably just because of the inability to understand what other people are referring to.”

Comprehending what causes humans’ brains to make decisions could potentially help people with autism, schizophrenia, or other neuro-developmental and neuro-psychiatric disorders. Researchers could better shape and reinforce skills that allow people to understand others, as well as potentially identify those at risk for developing these conditions.

Eye-tracking could also be used in business-related functions, Platt adds.

“This is a great opportunity to take this technology out of the lab and into consumer environments where we can explore the effectiveness of advertising. We can explore product displays. We can look at how people are using information about their environment to guide purchasing decisions, to guide decisions about whether to invest.”

For the peacocks, that investment equates to something along the lines of which partner to pick or whether to fight a rival. Different end goals, unquestionably, but driven perhaps by the same internal decision-making processes. Platt and his team may need to employ some additional eye-tracking goggles to find out.

Photo: Platt and colleagues put trackers, like the one seen here, on peacocks to learn where the birds looked most during the mating process. The trackers included a helmet that held a camera, plus a backpack with a data transmitter.

Peacocks, Eye Tracking, and the Brains Behind Decisions