Inside Rensselaer
* Left or Right? Early Detection of Penalty Kicks Revealed
In the split second before foot meets ball, a soccer player’s body betrays whether a penalty kick will go left or right, according to recent research in cognitive science.
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Left or Right? Early Detection of Penalty Kicks Revealed
In the split second before foot meets ball, a soccer player’s body betrays whether a penalty kick will go left or right, according to recent research in cognitive science. That could explain how some top goalkeepers are able to head off a penalty kick, diving in the correct direction in advance of the kick.

Gabriel Diaz, who completed his doctorate in cognitive science this summer, used motion capture technology — similar to that used in computer-generated graphics — and computer analysis to identify five early reliable indicators of which direction a ball will ultimately be kicked. His work also suggests that successful goal-keepers may be picking up on four of those five early reliable indicators.

“When goalkeepers are in a penalty situation, they can’t wait until the ball is in the air before choosing whether to jump left or right — a well-placed penalty kick will get past them.” — Gabriel Diaz

“When goalkeepers are in a penalty situation, they can’t wait until the ball is in the air before choosing whether to jump left or right — a well-placed penalty kick will get past them,” Diaz says. “As a consequence, you see goalkeepers jumping before the foot hits the ball. My question is: Are they making a choice better than chance (50/50), and if so, what kind of information might they be using to make their choice?”

Diaz’s work took advantage of Associate Professor Brett Fajen’s Perception and Action (PandA) motion capture lab. The lab uses behavior and action to draw insights into how our minds work. Diaz gathered data on college-level penalty kickers using more than 40 sensors placed on 19 major joints of the body.

Diaz tested 27 potential tells — 12 drawn from sports literature and 15 from a computer analysis of data drawn from actual kicks. Of the five indicators Diaz identified, two were specific movements — the angle at which the non-kicking foot is planted on the ground, and the angle of the hips as the kicking foot swings forward—while the other three are more complicated patterns of coordinated movement that were identified with the aid of computer analysis of the player’s body movements throughout the kick.

A distributed movement is complex, but, as Diaz’s work indicates, some people may be using it — however unconsciously — to inform their judgment as to which direction the ball will go. In the second part of his work, Diaz asked subjects to view motion capture animations of the kicks — which appear as dot figures — and pick which direction they thought the ball would go. An analysis of the subjects’ responses showed that successful “goalkeepers” may be picking up on four of the five indicators he identified.

To read more, go to http://news.rpi.edu/update.do?artcenterkey=2745.

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Inside Rensselaer
Volume 4, Number 14, September 24, 2010
©2010 Rensselaer Polytechnic Institute
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