Parkour at London's Southbank/Waterloo Bridge.

Parkour at London's Southbank/Waterloo Bridge.


Six ways your body changes your perception

*For our full coverage of AAAS 2016, check out our meeting page.

Can you jump that gap? Will you even try? Your visual system helps you make such decisions by warping and stretching the things you look at according to your physical traits or abilities, says Jessica Witt, a cognitive psychologist at Colorado State University, Fort Collins. Rather than showing us the world as it is, our vision toys with things like slope and distance. The harder a task, the more it seems to magnify before our eyes. These visual biases may have evolved to help us make quick decisions, letting us know at a glance which tasks to tackle. At the annual meeting of AAAS (which publishes Science) in Washington, D.C., Witt described several ways our physical abilities change what we see.

Successful batters see bigger balls

In a 2005 study, Witt and her colleagues snagged softball players after a game and told them to choose—from several circles printed on a poster—the one that was the same size as a softball. Athletes who had a good night at bat overestimated the size of the ball, whereas those who kept missing underestimated the ball’s size. In a similar experiment, Witt found that golfers who sank more putts judged golf holes as larger.

Crappy kicks warp the goal

In the softball experiment, it wasn’t clear whether people really saw things differently or just misremembered them. To find out, Witt turned to field goals in U.S. football, where players must kick a ball over a crossbar that connects two vertical uprights. After several field goal attempts, participants adjusted a small model made of PVC pipe to match the proportions of the goal. People who kicked the ball too low set the model crossbar higher, whereas those who kicked the ball too wide set the model uprights closer together. People could look at the real goal while adjusting the model, so the findings suggest they really saw the goal differently.

Parkour athletes see shorter walls

In parkour—an activity that evolved from obstacle course training—athletes vault, leap, and climb through the urban environment, often launching themselves to the tops of walls. In a 2011 study, Witt and her colleagues asked both parkour experts and novices how well they thought they could climb a given wall and then asked them to estimate its height. Parkour novices saw the walls as taller than they actually were, whereas experienced parkour athletes tended to see walls accurately.

“Reaching” tools can make objects look closer

Even reaching for the remote control could mess with perceived distances. In a 2005 study, Witt and her colleagues asked participants to estimate the distance to a dot on a table. People consistently underestimated the distance to dots that were close enough for them to reach. They also overestimated the distance to dots that were out of their reach. When participants were given a conductor’s baton, their perceptions shifted again: Dots in reach of the baton appeared closer than they actually were. But this shift only happened if people planned to use the baton; when they just held it, the illusion went away. This suggests that our visual system warps reality to help us plan action.

Heavy backpacks make hills look steeper

In a classic earlier study that Witt referenced, researchers asked participants at the base of a hill to estimate the hill’s slope. It looked steeper to people who were tired, elderly, or wearing a heavy backpack

Obese people see things as farther away

Building on the backpack study, Witt found that distances look farther to people when they weigh more. She and her colleagues went to a Wal-Mart and asked shoppers to estimate the distance from where they stood to several cones on the ground. Obese participants saw the cones as farther away than people who fell in the “normal” range or were only moderately overweight. The results were dramatic; an extra 200 pounds of body weight roughly doubled peoples’ estimates. Such visual biases could make it harder for obese people to adopt an active lifestyle, according to Witt.