It is tempting to think of our eyes as video cameras that take in information about the world and try to give us a reasonably accurate picture of what is going on in the outside world.

Key arguments against this way of thinking about vision were made by JJ Gibson, who developed an ecological theory of how we perceive the world starting in the 1950s.  His approach focused on asking what vision is for.  He pointed out that the main function of vision is to help us perform actions in the world, and so our visual system should give us information that will help us to act effectively.

That means that our goals can influence what we see.  In a classic study, Bruner and Goodman found that poor children judged the sizes of coins as larger than well-off children.  The idea is that if you really need a coin, then you will actually think it is larger than it is. 

More recently, Dennis Proffitt and his colleagues have found that people looking at hills they will have to climb judge the slopes to be steeper when they are wearing a heavy backpack than when they are not.  The judged slope is an indicator of the amount of effort it will take to climb the slope, so when it feels like it will be hard to climb, the slope appears steeper.

Jessica Witt has explored a similar issue in sports.  Her work finds that baseball batters see the ball as larger when they are hitting well than when they are not.  Similarly, putters tend to see the hole as larger when they make a putt.  In some way, confidence in these sports skills influences success.

A paper in the April 2012 issue of Psychological Science by Jessica Witt, Sally Linkenauger, and Dennis Proffitt suggests that changing the way people see something can also influence their skill.  In their study, they had people make a series of 10-foot golf putts.  To influence people’s perception of the size of the hole, they made use of a classic visual illusion called the Ebbinghaus illusion.  In the Ebbinghaus illusion, a circle in the center is surrounded by other circles.  When the surrounding circles are large, then the circle in the center looks smaller than when the surrounding circles are small.

Ebbinghaus Illusion

The Ebbinghaus Illusion. A circle appears smaller when it is surrounded by large circles than by small ones.

 To create the Ebbinghaus illusion with the golf hole, circles of light were projected on the putting surface.  When the circles were small, the golf hole appeared larger than when the circles were large.  When the golf hole appeared large, participants in the study made more putts than when it appeared small.  The effect was not huge.  Participants made about 10% of the putts when the hole appeared small and about 17% when it appeared large.  But it was statistically reliable. 

This effect is interesting, because most studies show that goals and performance influence perception.  For example, the heavy backpack makes the hill harder to climb, which makes the slope appear steeper.  This study goes the opposite way.  It shows that influencing the way people perceive the world can influence how they act on it.

Of course, more work needs to be done to understand why this effect occurs.  In putting, for example, it is possible that when the hole appears larger, people are more confident and so they are willing to hit the ball a little harder, and so they are less likely to miss putts by being short of the hole.    

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