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Processing speed in the blink of an eye

By Lee Bowman

How the heck does any slugger make contact with a fastball going 90 miles per hour? Or a pedestrian not make contact with an oncoming car doing 50 mph?

Some new research suggests the skill of tracking fast-moving objects may lie as much in the visual processing center of the brain as it does in the center of the eye.

The human eye is only so-so at tracking movement. The retina at the back of the eye captures light and transfers images to the optic nerve. Only the center of this structure, an area called the fovea, gives us our sharpest vision and is best able to track moving objects.

But this part of the eye can only focus on about 2 percent of our visual field (think smaller than a fingernail seen at arm’s length). The remaining field of peripheral vision mostly detects motion, but can’t track how something is moving.

That’s why a pitched baseball seems to move so much that it rises or curves — it’s actually moving into the less-capable field of vision. The same thing can happen when judging the path and speed of cars, tennis balls or a charging lion.

Of course, many athletes train hard to keep their central vision in focus, their “eye on the ball.” Vision-training tools — ranging from strings and colored balls to strobe glasses to special videos — are part of locker rooms and equipment rooms around the world.

But it may be that vision training also tunes up a section of the brain’s visual cortex called V5. This region acts as a booster that allows the brain to register what we’re seeing more quickly, helping to overcome a one-tenth-of-a-second lag between sight and recognition.

Looking at that 90 mph fastball, thrown from 60 feet, 6 inches away, a batter only has about 0.4 seconds to react, so a 0.1-second boost is huge.

Researchers at UC Berkeley have been studying the V5 region for more than year, first using a magnetic stimulation technique to disrupt the motion-prediction process.

Then, they conducted brain imaging on six volunteers as they viewed a two-part visual illusion — a series of flashes shifting against different backgrounds. The V5 region fired up as the subjects tracked and interpreted where the flashes were headed. Results of their study were published in the journal Neuron last month.

The research should help not just with understanding batting averages, but also in diagnosing and treating a variety of brain disorders related to impaired motion perception. It also adds to the overall understanding of brain circuitry, the scientists said.

Still more research suggests that fatigue may affect this process. Back at the plate, another new study indicates that major league players’ judgment of the strike zone worsens for many as the season goes on. Batters who play a full season typically have 600 to 700 plate appearances over 162 games.

Researchers at Vanderbilt University Medical Center in Nashville looked at the frequency at which batters swung at pitches out of the strike zone during the 2012 season, sorting the data by month for all 30 Major League Baseball teams. They found that batters were more likely to swing at bad pitches in September than in April on 24 of 30 teams, and on average, all teams were more free-swinging near the end of the season.

The team also analyzed data from the 2006 through 2011 seasons, finding a pattern of decline that could be predicted from start to finish in each one.

Dr. Scott Kushner, an assistant professor of sleep and neurology and leader of the study, said the decline is likely due to fatigue that develops over the course of a season through frequent travel and few days off. He presented the study during a meeting of the Associated Professional Sleep Societies in Baltimore.

He said it may be possible for teams to improve late-season strike zone judgment by using fatigue management practices, such as more days off for players in the middle and latter parts of the season.

A second fatigue-related study, presented at the same conference by researchers from Martha Jefferson Hospital Sleep Medicine Center in Charlottesville, Va., showed that professional baseball players who self-reported higher daytime sleepiness scores were much less likely to still be in the league three years later than those who did not.

— Contact Scripps health and science writer Lee Bowman at [email protected]

Scripps Howard News Service

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