Science Brief

Action and visual perception

What we see is biased by what we can do.

By Jessica K. Witt, PhD

Jessica WittJessica Witt is an associate professor at Colorado State University. She earned her PhD from the University of Virginia in 2007, and her BA in psychology and computer science from Smith College. Witt won the Janet Taylor Spence Award for Transformative Early Career Contributions from the Association for Psychological Science in 2015 and the Steve Yantis Early Career Award from the Psychonomic Society in 2014. An athlete herself, having won a gold medal on Team USA at the World Games Ultimate Frisbee Championships in 2005, Witt studies spatial perception in athletes and in all people as they perform actions such as walking, running, jumping and throwing. Her research is funded by the National Science Foundation. Author website.



Athletic experiences and anecdotes challenge several fundamental assumptions about how vision works. According to vision scientists, what we see is a direct reflection of the optical information that enters the eye. But according to athletes, balls can appear larger or to be moving slower on days in which they are playing well or are “in the zone.” Given that the optical information is the same, the claim that the perceptual experience differs depending on the athlete’s physical abilities suggests that what we see is more than meets the eye. Through rigorous empirical testing in my lab and in the labs of others, we have explored whether these athletic anecdotes reflect psychological reality.

Effects of action on spatial perception

Figure 1. Posterboard shown to participants in the softball study.
Figure 1. Posterboard shown to participants in the softball study.
As part of our initial investigation, we ditched the traditional laboratory setting and went out to the ballpark. Following a city-league softball game, I lured the players to my booth with promises of Gatorade and asked them the size of the softball. Specifically, I showed them a posterboard with different sized circles and asked which circle was the same size as the softball (Figure 1). I then collected information to calculate their batting performance for the game played that night. The data showed that perceived ball size was related to performance: those who hit better than others saw the ball as bigger (Witt & Proffitt, 2005).


We then did a similar study on amateur golfers. Again, we showed the athletes a posterboard with different sized circles and asked which circle was the same size as the hole. Golfers who were playing better than others selected a larger circle, which indicates that they saw the hole as bigger (Witt, Linkenauger, Bakdash & Proffitt, 2008).

This research has generated a lot of controversy because vision is supposedly determined by optical information received by the eye, not by the action of the perceiver. However, in our studies, even though the optical information was the same, people did not necessarily perceive the world as it was. These studies suggest that people see the world in terms of action and performance outcomes. That is, people see the world in terms of the actions that they can perform, and they see the world in terms of the actions that they cannot perform. Vision scientists who doubted whether action could influence vision sought alternative explanations to account for our data. For example, they questioned whether softball or golf performance impacted vision, or if those who saw the ball as bigger therefore performed better. The correlational data we had collected could not speak to this issue, so we ran another study.

We brought in 23 collegiate athletes who had no experience kicking field goals in American football and asked them to estimate the size of the goal (Witt & Dorsch, 2009). We then gave them 10 tries to kick field goals from the 10-yard line, and we recorded their kicking performance. At the end, we asked them to estimate goal size again. Prior to kicking, there were no differences in perceived goal size across those who kicked well and those who kicked poorly. But after kicking, there were large differences in perceived goal size (Figure 2). Those who kicked well perceived the goal to be bigger, and those who kicked poorly perceived the goal to be smaller compared with their prekicking perceptions. The data shows that performance can influence perception. In addition, the way a kicker missed impacted perception. Those who missed because they did not kick the ball high enough perceived the cross bar as taller, and those who missed because they kicked the ball too wide perceived the uprights as narrower. Vision is sensitive not just to performance in general but also to how a person succeeds or fails.

Perceived size is plotted as a function of whether perceptual judgment was made before kicking (left) or after kicking (right).
Figure 2. Perceived size is plotted as a function of whether perceptual judgment was made before kicking (left) or after kicking (right) and as a function of the number of successful kicks (out of 10). Each point represents data from one participant, and lines represent linear regression. Higher values of aspect ratio reflect perceiving the goal as bigger.

We and others have conducted similar studies across a wide range of sports. More skilled swimmers perceive underwater targets as closer compared with less skilled swimmers (Witt, Schuck & Taylor, 2011). In addition, swimmers wearing fins or flippers see underwater targets as closer compared with swimmers who had taken off the fins. Tennis players see the ball as moving slower when they successfully return the ball than when they missed the return (Witt & Sugovic, 2010). And tennis players returning better than others saw the net as lower. Skilled archers who are shooting better than others see the target as bigger (Lee, Lee, Carello & Turvey, 2012). People playing a video game similar to Pong perceive the ball as moving faster when it is more difficult to hit than when the ball was easier to hit (Witt & Sugovic, 2010). For people trained in the sport of parkour (or urban climbing), walls don’t look nearly as tall (Taylor, Witt & Sugovic, 2011).

These effects of performance on vision are not limited to athletes. They happen in all of us. Hills appear steeper and distances appear farther to a person who is fatigued, hungry or carrying a heavy backpack (Bhalla & Proffitt, 1999; Sugovic, Turk & Witt, 2016; Taylor-Covill & Eves, 2013, 2014, 2016). Objects look closer and smaller when they are easier to reach and grasp (Linkenauger, Bulthoff & Mohler, 2015; Linkenauger, Leyrer, Buelthoff & Mohler, 2013; Linkenauger, Witt & Proffitt, 2011; Linkenauger, Witt, Stefanucci, Bakdash & Proffitt, 2009; Osiurak, Morgado & Palluel-Germain, 2012; Witt, Proffitt & Epstein, 2005). The world is perceived, not in terms of an objective reality, but in terms of the perceiver’s ability to act, including whether or not the action is possible as well as level of performance. Spatial vision is biased by action.

Because of these biases, vision is dynamic and tells you what you can do and what you cannot do.  When an object appears farther away, that bias tells you the object cannot be reached. When a hill appears steeper, that bias tells you the hill cannot be climbed, at least not without expending an enormous amount of energy. When the ball appears faster, that bias tells the perceiver not to expect to hit the ball.

Extending the findings

Why might vision be set-up to work in this way?  Why doesn’t vision provide an objective image of the true environmental layout?  Perhaps these biases of action on vision are useful for planning and selecting future actions. Vision tells us what we can and cannot do so that we don’t have to think about it.  Vision saves us the trouble of having to figure it out.

We do not have to think about whether or not we can reach; vision tells us that we can, or vision tells us that we cannot. The process is so automatic that we take it for granted. We are not aware of the impact that our vision has on our decisions and actions. For the most part, this is ok. Vision keeps us safe. Seeing the edge of the cliff as closer, or the distance to the bottom as farther, helps keep us a safe distance from the edge of the cliff. Seeing a staircase as steeper keeps us from overly-exerting ourselves to exhaustion by helping us choose to take a nearby escalator instead (Eves et al., 2014). But sometimes vision sends us astray. Sometimes we have to fight what we see to accomplish the change we desire.

For example, vision in people with obesity reveals a bias due to body weight. Distances appear farther and hills appear steeper to people who weigh more than others and would therefore have to exert more effort to traverse the space (Sugovic et al., 2016; Taylor-Covill & Eves, 2016). This means that for people who weigh more, perception is biased to lead them away from making active lifestyle decisions. A hill that looks moderately difficult to ascend for one person might look impossibly steep to ascend for someone with obesity. And if perception makes it look impossible, one may be less likely to attempt to ascend the hill, or ascend the staircase. It is reasonable to suggest that these visual biases can create a vicious cycle by which active lifestyle choices are discouraged.

Someone with obesity who wants to lead a more active lifestyle will have to fight the biases within their vision. They will have to choose to take actions for which their vision is telling them not to do it. These biases in vision mean that inactive people with obesity may be up against greater barriers to making these healthy and active decisions.

Let’s take another example of when these action-based visual biases might create obstacles. I was thinking about the idea that when you hold a hammer, everything looks like a nail. If that was true, what did it mean if you were holding a gun? Does everything look like a shootable target? In an experiment we conducted to address this question, participants viewed images of a masked person holding either a gun or a gym shoe (Figure 3). The participants’ task was simple. If they saw a gun, they were to raise their arm and point to the masked person, and if they saw a shoe, they were to lower their arm and point to the ground. Work like this had been done before (e.g. Correll et al., 2002), but no one had ever manipulated the perceiver’s potential for action. An undergraduate student researcher, who created these images, asked participants to complete the same task but while holding a gun or a squishy rubber ball. Participants completed over 100 trials, and we looked at their perceptual accuracy. Specifically, we looked at the kinds of errors that they made. We looked at whether their perceptions were biased when holding the gun. And we found something alarming. When our participants held a gun, they were more biased to perceive the person in the images as also holding a gun (Witt & Brockmole, 2012). The act of wielding the gun created a bias in their vision to see guns.

Example of stimuli used in studies on visual biases created by wielding a gun.
Figure 3. Example of stimuli used in studies on visual biases created by wielding a gun.

Again, the perceiver’s ability to act, in this case, due to wielding a gun, generated biases in their vision. When they had the ability to shoot, their vision was biased to see guns even when a gun was not present.  Action biases vision.

Sometimes the biases that action creates in vision are useful. They can keep you a safe distance from the edge of a cliff. The biases can help you regulate your energy expenditure and keep you from exhaustion. They can help you decide which path to navigate, or which object to grasp, or which walls to attempt to climb over. They can help you decide which teammates to throw to and which teammates are too far away. But sometimes the biases that action creates in vision are harmful. They can prevent you from making active lifestyle decisions, and they can make you see dangers that don’t exist. Vision is not an objective picture of the physical world, but rather is a window into your own abilities, and your own potential for action. Vision is as much about you as it is about the external world.

Acknowledgements

Witt would like to thank her wonderful collaborators and students over the years, and the National Science Foundation for supporting this research (BCS-0957051, BCS-1314162, BSC-1348916, and BCS- 1632222).

References

Bhalla, M., & Proffitt, D.R. (1999). Visual-motor recalibration in geographical slant perception. Journal of Experimental Psychology: Human Perception and Performance, 25(4), 1076-1096.

Correll, J., Park, B., Judd, C.M., & Winttenbrink, B. (2002). The police officers's dilemma: Using ethnicity to disambiguate potentially threatening individuals. Journal of Personality and Social Psychology, 83, 1314-1329. 

Eves, F.F., Thorpe, S.K.S., Lewis, A., & Taylor-Covill, G.A.H. (2014). Does perceived steepness deter stair climbing when an alternative is available? Psychonomic Bulletin & Review, 21(3), 637-644. 

Lee, Y., Lee, S., Carello, C., & Turvey, M.T. (2012). An archer's perceived form scales the "hitableness" of archery targets. Journal of Experimental Psychology: Human Perception and Performance, 38(5), 1125-1131.

Linkenauger, S.A., Bulthoff, H.H., & Mohler, B.J. (2015). Virtual arm's reach influences perceived distance but only after experience reaching. Neuropsychologia, 70, 393-401.

Linkenauger, S.A., Leyrer, M., Buelthoff, H.H., & Mohler, B.J. (2013). Welcome to wonderland: The influence of the size and shape of a virtual hand on the perceived size and shape of virtual objects. PLoS ONE, 8(7), e68594.

Linkenauger, S.A., Witt, J.K., & Proffitt, D.R. (2011). Taking a hands-on approach: apparent grasping ability scales the perception of object size. Journal of Experimental Psychology: Human Perception and Performance, 37(5), 1432-1441.

Linkenauger, S.A., Witt, J.K., Stefanucci, J.K., Bakdash, J.Z., & Proffitt, D.R. (2009). The effects of handedness and reachability on perceived distance. Journal of Experimental Psychology: Human Perception and Performance, 35(6), 1649-1660.

Osiurak, F., Morgado, N., & Palluel-Germain, R. (2012). Tool use and perceived distance: When unreachable becomes spontaneously reachable. Experimental Brain Research, 218(2), 331-339.

Sugovic, M., Turk, P., & Witt, J.K. (2016). Perceived distance and obesity: It's what you weigh, not what you think. Acta Psychologica, 165, 1-8.

Taylor-Covill, G.A.H., & Eves, F.F. (2013). Slant perception for stairs and screens: Effects of sex and fatigue in a laboratory environment. Perception, 42(4), 459-469. 

Taylor-Covill, G.A.H., & Eves, F.F. (2014). When what we need influences what we see: Choice of energetic replenishment is linked with perceived steepness. Journal of Experimental Psychology: Human Perception and Performance, 40(3), 915-919.

Taylor-Covill, G.A.H., & Eves, F.F. (2016). Carrying a biological "backpack": Quasi-experimental effects of weight status and body fat change on perceived steepness. Journal of Experimental Psychology: Human Perception and Performance, 42(3), 331-338.

Taylor, J.E.T., Witt, J.K., & Sugovic, M. (2011). When walls are no longer barriers: Perception of wall height in parkour. Perception, 40(6), 757-760.

Witt, J.K., & Brockmole, J.R. (2012). Action alters object identification: wielding a gun increases the bias to see guns. Journal of Experimental Psychology: Human Perception and Performance, 38(5), 1159-1167.

Witt, J.K., & Dorsch, T.E. (2009). Kicking to bigger uprights: Field goal kicking performance influences perceived size. Perception, 38(9), 1328-1340.

Witt, J.K., Linkenauger, S.A., Bakdash, J.Z., & Proffitt, D.R. (2008). Putting to a bigger hole: Golf performance relates to perceived size. Psychonomic Bulletin & Review, 15(3), 581-585.

Witt, J.K., & Proffitt, D.R. (2005). See the ball, hit the ball — Apparent ball size is correlated with batting average. Psychological Science, 16(12), 937-938.

Witt, J.K., Proffitt, D.R., & Epstein, W. (2005). Tool use affects perceived distance, but only when you intend to use it. Journal of Experimental Psychology: Human Perception and Performance, 31(5), 880-888.

Witt, J.K., Schuck, D.M., & Taylor, J.E.T. (2011). Action-specific effects underwater. Perception, 40(5), 530-537.

(10), 1341-1353.Perception, 39Witt, J.K., & Sugovic, M. (2010). Performance and ease influence perceived speed.

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