Beauty is not the only thing in the eye of the beholder.

Height. Distance. Effort.

As you try to gauge these things by eye, the answers depend on how short, or how tired, or how healthy you are.

In Dennis Proffitt’s Cognitive Science Laboratory, in the department of psychology, researchers and students study how people think about the spaces around them. Proffitt is a perceptual psychologist, with much of his research over the years focused on visual perception. How do we see the world around us? How does our individual view influence our decisions?

To demonstrate, he takes an observer to the top of the hill behind Newcomb Hall, where many of his early studies were conducted. Looking down the grassy bank toward Emmet Street, he asks how steep the hill looks.

The average person will say it’s about 50 degrees, Proffitt says. The hill is actually angled at 28 degrees, but it looks much steeper when looking down between the tips of one’s shoes.

Too steep to climb up or down? Not worth the energy to take it on? Unsafe? The brain makes all those calculations, with an eye toward protecting itself.

“Perception has a purpose to it,” Proffitt explains. We control the use of only 20 percent of the calories we eat or drink; the rest is used in basic metabolism. Of the amount we can control, 80 percent is spent on walking, he says. Our decisions on how best to use those calories are based on perception of our environment.

Over the years, Proffitt and his students have conducted studies all over Grounds, asking participants to calculate distance or incline in several ways, including the use of virtual reality headsets or blind walking—asking blindfolded participants to walk a distance equal to what they perceived. The basic estimate of distance or incline is complicated by the addition of bodies in motion and energy expenditure—for example, a heavy backpack.

“What you’re seeing is the way you fit into the world,” Proffitt says. “That is what perception is. This hill looks steeper if you’re encumbered, if you’re tired. The steepness is related to your physical fitness, it’s related to your age and to declining health. You’re seeing it as geometry scaled to your body.”

Vision is one of the most difficult tasks the brain performs, he says. Assessing what the eye sees, then making split-second decisions and taking action are complex mathematical problems the brain does countless times a day.

Pain is another factor in visual perception. Those in chronic pain see distances as longer and hills as steeper, he says. Even mental fatigue can affect the way people perceive.

The Cognitive Science Lab, known informally as the Perception Lab, began in 1979. Research has been funded by the federal Defense Department and NASA, by foundations such as the National Science Foundation, and by private industry such as Google, Intel and Disney. He and his students are working now with virtual reality headsets, tracking head and body movements in response to a virtual environment.

“We assume we experience the world as it is,” he says. But that’s not the case. Seeing is believing. And learning to see the world through someone else’s eyes should make people more sensitive to others, Proffitt says.

“Everybody lives in their own world,” he says. “That’s why it’s important to get everyone’s perspective.”