Keeping Your Eyes on the Ball May Be Essential

Originally Published: May 14, 2014 – 12:45pm, Inside Science News Service
By: Jessica Orwig, ISNS Contributor

(ISNS) – For the last 50 years scientists have conducted numerous studies to understand how baseball players can run, track and catch a fly ball. Many of those studies settle on an explanation that more or less stipulates what every coach will tell you: “Keep your eye on the ball.”

Without visual contact of the ball, a player is more likely to let his team down and miss the catch. But up until recently, no study had been able to prove this was the case in a real, ball-catching scenario.

Eye-tracking rig confirms that players must watch the ball to catch it.
Credit: chipgriffin via flick, 

For the first time, scientists have documented the eye movement of athletes running at full speed to catch fly balls. The results are the most convincing yet to support past notions that constant eye contact is essential to a successful catch.

In the past, scientists have attempted to study the eye movement of athletes by observing their gaze as they ran, or tracking their eye movements as they caught virtual balls in a confined, enclosed space. None of these studies, however, could say with absolute certainty that the catchers were always watching the ball.

Using headset technology capable of tracking pupil movement, Frank Zaal, a professor of medical science at the University of Groningen in the Netherlands, and two of his colleagues at the same university saw exactly what subjects saw as they ran to catch fly ball and reported the results earlier this spring in a paper in the journal PLOS ONE.

They discovered that participants, who each had at least 2 years of experience in ball sports, followed the ball with their eyes 95 percent of the time that the ball was in the air. They did this even when they were running at top speed.

Zaal and the team fired balls from behind a wall in the direction of the participants. This was so subjects could not anticipate where the ball would travel by looking at the direction the machine pointed before launching the ball. Participants would sometimes have to run forward and sometimes backwards to catch the ball.

“I think the main finding is that people keep looking at the ball, which tells me that they need continuous [visual] contact,” Zaal said.

The volunteers completed a total of 54 trials. Some balls were deliberately made uncatchable to test eye movement in those cases. Still, in those cases, the scientists found that subjects followed the ball more than 90 percent of the time it was airborne, until realizing they could not catch it.

Many scientists have studied the eye movements of people attempting to catch a ball, in order to better understand how the brain predicts changes in the environment.

“We’re always anticipating what’s going to happen next,” said William Warren, a professor for the Department of Cognitive, Linguistic and Psychological Sciences at Brown University in Rhode Island. Warren was not involved with the research.

How the brain solicits information so that it can anticipate an action, such as a ball’s direction of motion, is not well understood. Some, like Warren and Zaal, argue that the brain processes visual cues and then responds accordingly.

Another theory is that the brain is more like a computer that stores information over time and then extracts it when needed. According to this theory, fielders would not need to keep their eyes on the ball at all times. Once they developed a basic understanding of projectile motion, they could simply calculate where the ball would land from a quick glance and then run to that spot.

Such was the case during the 1954 World Series when Willie Mays turned his back to a fly ball and ran to the edge of the field before miraculously catching it.

Mays’ catch later spawned the flurry of studies that have since tried to understand whether that success was the norm or an exception.

“The fact that his catch is so famous is because it’s so rare,” said Warren. “People don’t ordinarily do that.”

But does the brain work from learned information or by reacting to updated information?

Perhaps it acts like both depending on the situations.

“That’s the hot debate,” Warren said. “There’s certainly a growing interest that we’re making predictions all the time and the school of thought is that that is what our brains are good at.”

Ultimately, Zaal is trying to understand how humans conduct general interceptive movements whether it’s catching a ball, picking up a cup of coffee or avoiding a moving vehicle. People are continuously updating their movements in response to their environment and this behavior could be passed down, Zaal said.

“At some point it would help things like robotics,” Zaal said. “One thing people are really good at is behaving in challenging environments where things are changing all the time and that’s something robots have trouble with.”

Inside Science News Service is supported by the American Institute of Physics. Jessica Orwig is a contributing writer to Inside Science News Service.

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