Ronaldo kicking golf balls
Monday, December 15, 2014
Cristiano Ronaldo (Real Madrid) is currently soccer’s best penalty kicker in La Liga with 35 goals in 37 penalties, which translates to a stunning 94.6% success rate. But really, how hard can it be? With a goal standing eight feet high and eight yards wide just 12 yards away from these professional soccer players, how could one fail to fire the ball past the goalkeeper?
Perhaps surprisingly, 29.2% of penalties missed the goal in shootouts since their introduction to the World Cup in 1978. It seems that hitting a soccer ball correctly to score a goal is not that easy after all.
Perception and action are tightly coupled. The way we act influences how we perceive the world. "Perception is not something that happens to us, or in us," writes Alva Noë in his book Action in Perception. "It is something we do."
Evidence for an action-specific account of perception, according to which people perceive the environment in terms of their ability to act in it, has been found across many different activities including throwing darts, golfing, and kicking field goals.
One consistent finding from this research is that when you are better at a task, you judge the action’s target as being bigger.
What might be more interesting for Ronaldo in terms of increasing his penalty kick success rate to 100% is the reciprocal relationship: namely that the way we perceive the world will influence how we act in it.
Good news for Ronaldo: Visual illusions that made a hole seem bigger did indeed result in better putting performance. There seem to be ways to improve action performance by tricking your perceptual system.
While the basic interplay of action and perception remains undisputed, the exact relationship does not seem to be as clear-cut as one might think. In their recent paper published in Attention, Perception, & Psychophysics, Kirsch, Königstein, and Kunde expected to replicate the positive relationship between movement performance and size estimates. What they found, however, was exactly the opposite: “The target was judged as smaller when it was easy, rather than difficult, to hit before as well as after the movement.” According to these findings, Ronaldo would perceive the soccer ball as being much smaller than any of us would.
In order to understand the results, we need to take a closer look at the details of the experiment by Kirsch and colleagues. The figure below shows the important features of the procedure. In three experiments, participants were asked to hit a visual target presented on a screen by moving a stylus. Trials were initiated by moving the stylus to the start position upon which the target — a gray filled circle — was displayed. After half of the distance to the target was covered, visual feedback of the stylus position was removed. Participants had to press the stylus button after finishing the movement.
Once the movement was completed, participants received feedback on whether or not they successfully hit the target and were then asked to reproduce the size of the target by adjusting the size of a stimulus by pressing “+” or “-“ on the keyboard. This design allowed the authors to examine “relations between motor performance and perceptual judgments on a trial-by-trial basis.”
Both target size and movement distances were varied. To investigate the dependency of size judgments and motor performance, the spatial deviations of movement end points from the center of the targets were computed for each trial feeding into an index of motor variability (IMV) for each condition and participant.
As mentioned earlier, the direction of the observed effect was exactly the opposite of the predicted direction showing that participants estimated the target size to be larger after target hits than misses. However peculiar the outcome, it does seem robust. The negative relationship between hitting ability and perceived target size replicated across all three experiments, even when judgments were made before each pointing movement rather than after. That is, the mere preparation of a movement caused perceptual perturbations.
While unpredicted, this outcome could be due to at least two factors: One, when the task seems rather easy, the target position might appear closer than when the task seems more difficult. As in the Ponzo Illusion, an object that seems closer will be perceived as being smaller. Second, different degrees of task difficulty might be associated with changes in the degree to which you attend to the target. Directing more attention to a target could increase the effective spatial resolution of the visual system, which in turn might make an object look bigger than it actually is thus enhancing chances for a hit.
So why did other studies find different results? When I contacted the lead-author, Wladimir Kirsch, to ask about possible reasons for the discrepancy between the results of this study and previous findings, he pointed out that a major difference lies in the experimental design: While in other studies perceptual estimations were often first made after a series of motor responses, participants in this study were asked to make size judgments after every motor response.
According to Kirsch, the positive relationship between motor performance and size judgment reported previously might reflect more of a response bias. “I hit the target several times now, therefore it has to be big”. Such heuristics would be less common when making size estimates after every movement. While this might explain some of the differences observed, there is probably more to it. Stay tuned, Kirsch and colleagues are now looking more closely at the mediating effects of attention allocation and distance estimates.
In the meantime, Ronaldo might be advised to spend less time on strengthening his muscles, and more time on focusing his attention. Former England striker Alan Shearer says with regard to penalty pressure: “Your mind starts to play tricks on you. That walk is a long walk and a million things go through your mind. Your heart beats faster but you've got to believe in what you've trained to do.” Another real-world demonstration for the important and inevitable interplay of attention, perception, and (psycho-)physics.