Certain authorities (high-school math teachers, college journalism professors) would have you believe that objective truth is out there. But what might be true for a yardstick – that a yard is always 36 inches – may be less than reliable, in a sense, for human beings.
That can be seen (pun intended) in a study about how lighter and heavier people perceive distances. In a paper published in Acta Psychologica, Purdue University and Colorado State University researchers asked 66 community members – recruited by researchers from outside a superstore – to estimate the distance of cones along a path that were set out at 10, 15, 20, and 25 meters. After making the estimate, participants took a survey in which they reported their height, weight, and how they evaluated their own weight (as “too low, a bit low, good, a bit high, or too high”). As measured by body-mass index, 23 participants had a normal weight, 21 were overweight, and 22 were obese.
The research team – led by Mila Sugovic, now a research manager at EurekaFacts and formerly a researcher at Purdue – found that for every additional hundred pounds of weight, people estimated distances to be 3.4 meters further. This falls in line with what psychologists call the “action-specific theory of perception”: Basically, people perceive their environments relative to their ability to act in it. So you judge distances relative to your ability to cross them. “People who weigh more must transport a larger mass, and it is also energetically more costly, therefore they perceive distances as farther than do those who weigh less,” Sugovic explained in an email. The findings also suggest that your eyeballs don’t work in a vacuum; there are non-optical factors involved in visual perception – in this case, body size. Doubly interesting, those self-ratings of being large or small didn’t match with the distance estimations. Your perception “doesn’t care” about how you evaluate how small or thin or attractive you are, says Jessica K. Witt, a Colorado State psychologist who’s a co-author of the study.
“It’s about the about the physical realities of one’s body and the physical realities of the environment,” Witt tells Science of Us. “The findings are that what you see, in this case distances, isn’t just about what’s really out there. It isn’t the same as measuring a distance with a ruler, it’s not objective in that sense. Instead, what perception is doing is telling its perceiver about the world as that world relates to the perceiver.”
The finding falls in line with the growing fields of embodied cognition and ecological psychology, which contend that your body fundamentally frames your mental life. For example, a 2005 study of Witt’s found that softball players who had higher batting averages literally saw the ball as bigger than it was, and a 1995 study by University of Virginia psychologist Dennis Proffitt found that as people get fatigued, they estimate the slant of hills to be higher. Similarly, fit people will see less of an incline than folks who are out of shape.
The applications of this are as liberating as they are frustrating. An obese person can’t change the way they see their environment, Sugovic says, but if they have the knowledge that their perception that a hill is too steep or a distance too far, they might be more motivated to overcome it. There’s an application for losing weight, too: You might judge that last mile of your run around Prospect Park to be way too far to keep hustling, but that might just be your body telling you that it’s fatigued. But if you remind yourself that you can tolerate discomfort, you really can.