We usually believe that what we see is a true representation of what’s there. The basic model of vision is that the eyes receive sensory information, the brain processes it, and then you're able to act on what you see, like dodging someone in your path, or grabbing for a cookie.
But simple optical illusions (or looking at “The Dress”) quickly reveal that your brain sometimes alters what you perceive based on context. Two lines of the same size can appear to be different, depending on the other lines that frame them. Your brain can fill in visual information that falls into your eye's blind spot. If you look at "The Dress" and your brain thinks it’s cast in shadow, you’ll find it to be a different color than a friend standing next to you—even though you’re both receiving the same sensory information.
“People tend to have this impression, first of all, that they see things accurately, that they see the world as it really is,” says Jessica Witt, a cognitive psychology researcher at Colorado State University. “And there’s a lot of research in vision to show that’s not true.”
Witt started working on visual perception with psychologist Dennis R. Proffitt at the University of Virginia, where Proffitt was finding that people often overestimate how steep hills are—and do so even more if they are tired, elderly, out of shape, or wearing a heavy backpack. He found that if people had just gone for a run, or were positioned at the top of a hill on a skateboard, they were also more likely to report seeing a hill as steeper than it really was. Their findings seemed to be showing that actions, past and potential future ones, could impact what people saw.
Witt has continued, over the past 15 years, to study the effects of actions on perception, turning at first to athletes, who regularly combine the two. For a 2005 study, she went to softball fields with a poster board with different-sized circles on it, asking players to pick the circle that matched the size of the ball. She found that the players with better batting averages reported the ball as bigger, and those who didn’t play as well that day thought the ball was smaller than it really was. In a similar study with golf players, she found that golfers who were playing better judged the size of the holes to be larger.
It’s not always that things look larger, she says—tennis players returning more hits judged the nets to be lower, and the ball to be moving more slowly. Obstacle courses look smaller for those who have more experience with them. When she studied athletes kicking field goals, she found that those who kicked more goals perceived the height of the cross bar to be shorter compared to those who kicked less successfully. At the same time, they perceived the uprights to be farther apart. If a participant kicked the ball too wide, they perceived the uprights as narrower, and if they missed because they couldn’t kick it high enough, they saw the cross guards as taller. Perception, she says, seemed to be link to the specific actions an individual was taking.
She’s applied this finding to non-athletic people as well, showing that giving people a tool to reach for something can decrease a perceived distance, giving flippers to swimmers made underwater targets appear closer, and that chronic pain and being obese can both increase your perception of distance.
Witt thinks that actions provide a filter through which the brain processes visual information. “If you were looking at the world through the context of 'I’m tired, my energies are depleted,' then the brain produces a very different kind of visual, a different perception, than if you feel high energy and you have all those energetic resources available to you," she says. Witt says that in many cases—like for steep hills, and perceived distances—the brain may be trying to conserve that energy. Studies have shown that when stairs are perceived as steeper, people are more likely to find an alternative, like an escalator.
“Another way to think of it, is the visual system is incorporating action to help make its best guess,” she says. “We don’t really know how steep that hill is, but I’m going to make my best guess. And my guess is going to be a lot steeper when I’m tired.”
For balls and goals appearing smaller and narrower, it's almost like “the perceptual system offers us self-serving justifications for bad performance,” wrote neuroscientist Christof Koch in an essay about Witt’s work in Scientific American Mind. “But there is likely some value here, evolutionarily speaking: If people perceive the goal as higher or smaller than it actually is, they will aim more precisely the next time.”
But the idea that what we see is so easily impacted by action hasn’t gone without dispute. Witt’s faced very vocal responses to her research, which she thinks is because she’s upended the typical chronology of “see, think, act,” by finding that “act” can influence that sequence earlier than was thought possible.
Two of her critics, Brian Scholl and Chaz Firestone from the department of psychology at Yale University, have published on the pitfalls they think her research encounters: that the sample sizes are too small, or that it’s hard to discern between perception and judgment—did participants really see the hill as steeper, or just remember it as such? "I think the idea of action changing how we see is fascinating," Scholl says, but also that he considers the findings to be generating more excitement than might be warranted. "The science itself doesn't run nearly as far as it would need to," he says.
One of Scholl and Firestone's most pressing concerns is about response bias: they think that in many perception and action studies, the participants can easily guess the purpose of the study, and as a result, their responses can be skewed. For example, if someone was asked to gauge how steep a hill was, and then given a heavy backpack and asked again—they might infer that the hill is supposed to look steeper, and then perceive it as such.
Witt has performed a new study, recently published online in Psychological Science, to directly address the response bias issue. She used a computer game, similar to Pong, which she says has been their most consistent and robust way to elicit the influence of action on perception. People in the study use a joystick to block a ball with a paddle of varying sizes, which makes the task easier or harder. When asked about the speed of the ball, those with smaller paddles perceived the ball as faster—even though the ball's speed remained the same no matter what paddle size they had.
This time, after the participants played the game, Witt gave them a survey, explicitly asking if they knew the purpose of the study. Only 25 percent guessed correctly, and Witt says that when she compared their results to others who didn’t guess the study’s purpose, they still showed the same effect—that the perception of ball speed was related to paddle size. “It pretty strongly rules out the critics' claim of this being about response biases,” Witt says.
Witt also included another suggestion from Scholl and Firestone into this study: an element of misdirection. She gave some of the Pong games a blue background and some, a red one. “It was totally irrelevant to our purpose,” she says. “But we hoped it would mislead participants. And we did find that several participants said [the goal of the study] was to see if the ball moved faster when the background is red.” Still, even the participants who incorrectly guessed the study’s purpose showed the Pong effect, Witt says.
Scholl still isn't sold. "I don't ultimately find this new study to be convincing, but I am very glad to see this kind of work appearing," Scholl says, "These are exactly the sorts of careful and critical controls that have been sorely missing from this literature since its inception. And we should indeed be holding this sort of work to a high standard. In part, this is for scientific reasons–since this work flies in the face of everything we know about how perception works. And in part, this is for social reasons—because the proponents of such effects argue that they merit possible changes in policy in real-world contexts ranging from gun violence and vehicular safety to athletic performance and medical diagnosis."
Scholl continues to finds many elements of this effect unbelievable, and contradictory to other ways that your brain can distort perception. "Optical visual illusions… persist despite your beliefs and intentions (or what language you speak, or how you're acting, etc.)," he says. " But this work, in contrast, suggests that what you see can change willy-nilly depend on what you're doing– or even just what you intend to do." Scholl says that the survey Witt included is only the first of many steps which would lead to him being convinced.
But there are voices on both sides, says Laura Thomas, an assistant professor of psychology at North Dakota State University who also studies the effects of action on perception. "I actually think that [Witt] is being very careful about trying to address the criticisms that have been posed there," she says. "She’s doing science the way most of us try to, which is you come up with alternative hypotheses and you test those." Thomas's work focuses on the more subtle ways that action can impact how we take in visual information, like how different postures can affect how we receive information from touchscreen devices.
"This modular approach to vision has been an approach that’s been enduring and lasted for a very long time," Thomas says. "I think that challenging that is important in terms of shifting the way we as researchers are thinking about the issue."
There’s so much lingering controversy around this work, that Witt says that most of her recent research has been similar to this new study: designed specifically to address a critique. She has a lot more questions about the specifics of how this effect works. What does it mean that it's experienced differently than a "typical" illusion? Does it also apply to cognitive or artistic efforts, not just physical ones? And what exactly is going on in the brain to produce these changes? She hopes that once the fundamentals of the debate are better resolved, she can go on to study it in more detail.
"I will say that as hard as it is at times, I feel that the critics have really pushed the science in a good way," she says. "I’m an athlete, and I know the way to be my best is to have the best competitors to go against."
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