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Tracking Fastballs

Tracking Fastballs Photo Credit: Clipart.com

To hit a fastball, a batter’s brain has to predict when it’ll come across the plate.


Transcript

The brain’s fastball trick. I’m Bob Hirshon and this is Science Update.

(Announcer: “And the pitch is swung on a miss. 95 mile-an-hour fastball, 0 and 1.”)

Major league pitches are too fast for batter's eyes to track directly. Signals from the eye take about a tenth of a second to reach the brain, and a fastball can travel over ten feet in that time. So how do batters ever hit ‘em? As psychologist Gerrit Maus of the University of California at Berkeley explains, the brain actually stays one step ahead of the eyes, by predicting where the ball really should be at any given time.

Maus:
So it’s analyzing the motion and then calculating where things should be by the time that this information is actually perceived.

In other words, what we perceive in any given moment is the result of that prediction, and not the moving object itself. It’s the same way we all track pesky flies or oncoming cars. I’m Bob Hirshon for AAAS, the Science Society.


Making Sense of the Research

Pro baseball pitchers routinely throw faster than 90 miles per hour. Obviously it's hard for even a major league slugger to hit such a fast-moving target. But sometimes they do. And they do it by using a phenomenon that happens in all of our brains every day.

It takes a tenth of a second for a nerve impulse from your eyes to reach your brain. That may seem very fast, and it is. Still, for any relatively fast-moving target—whether a car coming around a corner, a vase falling off a table, or hot coffee pouring from a pot—it's not fast enough to coordinate responsive movements, like stepping out of the way, catching the vase, or tipping the coffee pot back up before the mug overflows.

In other words, if a batter swung with that tenth-of-a-second lag between his eyes and his brain, a batter wouldn't swing until after the ball hit the catcher's glove. And we'd all run into that problem throughout the day. Even someone walking toward you at a typical speed can cover about six inches in a tenth of a second. That's enough of a difference to cause collisions, or turn a handshake or high-five into an awkward miss.

The brain compensates for the delay by adjusting what you actually see. (By “see,” here, we mean experience as a visual image, which is what people usually mean when they talk about seeing.) Instead of perceiving a moving target where it was when your eye detected it, you perceive it as being where it should be, based on an on-the-spot analysis of its speed and direction. Since our brains are very good at this, where the batter percieves the ball is usually, in fact, where the ball actually is. As a result, it's as if he's seeing everything and reacting in real time.

This is a difficult concept, because it implies that everything you experience through your senses is basically an illusion created by your brain. And it is. It's just that our brains and sensory organs have evolved to make that illusion as true to reality as possible, or at least as necessary for our purposes: We are always in the presence of colors we can't see, sounds we can't hear, and odors we can't smell—all of which some other animals perceive naturally, as clearly as we can see red, hear a piano note, or smell chocolate.

Going back to motion, scientists can study the difference between our brain's perception and reality with something called the “flash-drag illusion.” In this illusion, colored dots flash on a rapidly rotating background, and they appear to move back and forth. When the video is slowed down, however, we can see that the dots actually stay in the same place. Our brain (incorrectly) uses the background as a clue that the entire image is moving, and predicts the location of the dots in the wrong place. Dr. Maus' team has used this illusion to identify areas of the brain in which a moving object is processed as it comes in from the eyes, and another area where it's already been corrected to predict where it ought to be.

Now try and answer these questions:

  1. Why can't we track motion accurately by just using the signal from the eye to the brain?
  2. How does the brain correct this so that we can judge a moving object's position accurately?
  3. What would happen if our brains didn't make this correction?
  4. Can you think of other everyday tasks that involve tracking fast-moving objects?

You may want to check out the October 18, 2013, Science Update Podcast to hear further information about this Science Update and the other programs for that week. This podcast's topics include: literary fiction's influence on social astuteness, why some people still fall for email spam, and how cell phones are transforming rural medicine.

For an example of the flash-drag illusion, see this short video from Berkeley Labs.

In the Science Update Curve Balls, hear how scientists are using math to model the motion of curveball pitches.

The Science Update Mona Lisa's Smile explains what one of the world's most famous paintings reveals about our visual perception.


Going Further


For Educators

For an example of the flash-drag illusion, see this short video from Berkeley Labs.

In the Science Update lesson Curve Balls, hear how scientists are using math to model the motion of curveball pitches.

The Science Update Mona Lisa's Smile explains what one of the world's most famous paintings reveals about our visual perception.


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