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Visual bias in soccer fouls.

The views expressed are those of the author and are not necessarily those of Scientific American.


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It's okay, Hope. I still adore you. (Image credit Wikipedia)

While I wouldn’t say that I am a soccer fan, I do find it hard to turn down watching large international sporting events, especially when the USA is doing well in the playoffs. I set a personal record for soccer-viewing last year during the men’s World Cup, so I would have been remiss to not watch the USA Women’s National Team in the quarter-, semi-, and finals this year (also, let’s face it, Hope Solo is dreamy). I’m sad that they didn’t win, but it was fun to watch, cheer, and hide from my boyfriend’s occasionally schizophrenic outbursts (he’s much more into soccer than I am). Congratulations are due to Japan and their excellent team. After watching the final match yesterday evening, I was reminded of a post I wrote last year after the USA men’s team was eliminated. Sports in general aren’t my usual beat, but I’m reposting it here because the paper was fun to read and the post was fun to write.

Originally posted on Jul 9, 2010.

There are many Americans like myself who only watch soccer during World Cup years, and because we aren’t as familiar with the nuances of the game as the die hard fans, the subjective refereeing is a foreign concept to us. We are a nation of people accustomed to instant replays, call challenges, and overturns. We simply don’t understand it when controversial calls are made and not challenged, or important calls are not made upon further review. In a soccer match, the referees only get to see a play once, but we can see what really happened over and over and over again (such is the gift and the curse of instant replay); thus, we demand to know why bad calls are allowed to stand.

FIFA’s stance on this subject has historically been that human error adds to the drama and pathos of their sport. FIFA general secretary Urs Linsi had this to say on the subject in 2005: “Players, coaches and referees all make mistakes. It’s part of the game. It’s what I would call the “first match”. What you see after the fact on video simply doesn’t come into it; that’s the “second match”, if you like. Video evidence is useful for disciplinary sanctions, but that’s all. As we’ve always emphasised at FIFA, football’s human element must be retained. It mirrors life itself and we have to protect it.”

More recently, in response to the American outrage at referee Koman Coulibaly’s decision to disallow a USA goal during the USA vs. Slovenia match in the 2010 World Cup, FIFA’s head of refereeing Jose-Marcia Garcia-Aranda said, “Some of them are not good decisions on the field of play and this for human beings, is natural. [...] We have excellent decisions on the field of play. Later, maybe with 32 cameras, thousands of people assessing this kind of situation, we realize these decisions were not fully correct.”

It is my understanding that FIFA is reluctant to bring in the technology necessary for video review because they do not want areas of the world that are too poor to afford that technology to be at a disadvantage. If this is the case, then perhaps we can think of ways to eliminate error without the use of additional technology that would sully the ‘humanity’ of the sport. To this effect, Kranjec and colleagues devised an experiment to test if the subconscious visual bias associated with left-to-right reading patterns causes a disparity in the likelihood of a foul being called on the exact same play when viewed from opposite directions.

English language cultures (along with many others) read from left-to-right on the page, which may instill a sense of preference and naturalness to left-right motion. Motion from right-left can be subtly and subconsciously jarring or uncomfortable for the viewer, a phenomenon which the authors cite is often exploited by the cinema industry (i.e., having heroes enter from stage left but antagonists enter from stage right). The authors hypothesize:

Given this bias for representing prototypical events from left-to-right, English speakers should be more likely to call a foul when the direction of play moves leftward. Below awareness, left-moving events should seem atypical and relatively debased compared to right-moving events. For soccer-knowledgeable participants making refereeing judgments in ambiguous situations, this perceptual-motor bias may serve to lower the threshold for calling a foul.

To test this, they recruited members of their university soccer team to examine photographs where two athletes were engaged in a confrontation that had a clear direction of movement (either left-right or right-left), where one player clearly had possession of the ball and the other player was clearly the challenger. The participants were forced to make snap judgements as to whether or not a foul was being committed. What the participants did not know was that they actually viewed each of the 100+ images twice: once in its original orientation, and once again as a mirror image to change the direction of play (numbers and letters were removed so that this would not be apparent). The authors found that on average, their participants called about 3 more fouls on right-left moving pictures than left-right moving pictures. While this is a small difference, it was found to be statistically significant. Given that they viewed the exact same images twice, once from each angle, and were more likely to call fouls on those images when they were moving from right-left, this would support the authors’ hypothesis that there is an inherent bias in favor of left-right movement and that the threshold of judgement for calling a foul is lowered when the referee is watching events unfold from right-left.

What does this mean for the game? As anyone who has ever watched a soccer game will know, fouls are very important to the outcome of the game. Fouls can result in free kicks or penalty kicks, which can often result in a goal, and the margin of winning scores is notoriously low. A bad call in a soccer game can much more easily influence the outcome of that game than in other sports, and if referees are naturally and subconsciously biased towards calling fouls during right-left motion, this can put one or the other team at an immediate disadvantage.

Soccer referees generally patrol the field using a diagonal system of control, meaning that they view one end of the pitch from left-right and the other end from right-left (there is an excellent diagram in the paper that illustrates this concept, which is free online since it is in PloS ONE). Because the teams switch ends of the field at halftime, the bias tends to equal itself out as long as the referee doesn’t switch diagonals, however there is currently no rule in place to stop the referee from doing so. FIFA may want to take this visual bias under consideration when advising their referees. However, recent news seems to indicate that after the events of the 2010 World Cup, they are open to reexamining their stance on instant replays. FIFA president Sepp Blatter said, “It’s obvious that after the experiences so far at [the 2010] World Cup it would be nonsense not to reopen the file. [...] Something has to be changed.”

Is it possible that the bias observed in this study was at play when referee Coulibaly made the call last year to disallow a USA goal during the USA vs. Slovenia match? Well… probably not, but it is possible. If you look at the screencap to the left, Coulibaly is circled in yellow and the general path of the ball is traced in red. From his vantage point, he would be viewing the play from right-left. Coulibaly is from Mali, where both the official language (French) and the lingua franca (Bambara) are read left-right, so it is not entirely unreasonable to assume that he would have the same left-right visual bias. It is possible that his threshold for foul-calling was lowered because of his vantage point and inherent bias, but we’ll never really know.


Alexander Kranjec, Matthew Lehet, Bianca Bromberger, Anjan Chatterjee (2010). A Sinister Bias for Calling Fouls in Soccer PLoS ONE, 5 (7) : doi:10.1371/journal.pone.0011667Site Meter

Michelle Clement About the Author: Michelle Clement has a B.Sc. in zoology and a M.Sc. in organismal biology, both from The Ohio State University. Her thesis research was on the ecophysiology of epidermal lipids and water homeostasis in house sparrows. She now works as a technical editor for The American Chemical Society. Like this blog on Facebook. Follow on Twitter @physilology.

The views expressed are those of the author and are not necessarily those of Scientific American.






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