May 8, 2013
Throwing a baseball is hard. As xkcd pointed out just yesterday, accurately throwing a strike requires that a pitcher release the ball at an extremely precise moment—doing so more than half a millisecond too early or too late causes it to miss the strike zone entirely. Because it takes far longer (a full five milliseconds) just for our nerve impulses to cover the distance of our arm, this feat requires the brain to send a signal to to the hand to release the ball well before the arm has reached its proper throwing position.
The one feat even more difficult than throwing a fastball, though, might be hitting one. There’s a 100 millisecond delay between the moment your eyes see an object and the moment your brain registers it. As a result, when a batter sees a fastball flying by at 100 mph, it’s already moved an additional 12.5 feet by the time his or her brain has actually registered its location.
How, then, do batters ever manage to make contact with 100 mph fastballs—or, for that matter, 75 mph change-ups?
In a study published today in the journal Neuron, UC Berkeley researchers used fMRI (functional magnetic resonance imaging) to pinpoint the prediction mechanisms in the brain that enable hitters to track pitches (and enable all sorts of people to envision the paths of moving objects in general). They found that the brain is capable of effectively “pushing” forward objects along in their trajectory from the moment it first sees them, simulating their path based on their direction and speed and allowing us to unconsciously project where they’ll be a moment later.
The research team put participants in an fMRI machine (which measures blood flow to various parts of the brain in real time) and had them watch a screen showing the “flash-drag effect” (below), a visual illusion in which a moving background causes the brain to mistakenly interpret briefly flashed stationary objects as moving. “The brain interprets the flashes as part of the moving background, and therefore engages its prediction mechanism to compensate for processing delays,” said Gerrit Maus, the paper’s lead author, in a press statement.
Because the participants’ brains thought these briefly flashing boxes were moving, the researchers hypothesized, the area of their brain responsible for predicting the motion of objects would show increased activity. Similarly, when shown a video where the background didn’t move but the flashing objects actually did, the same motion-prediction mechanism would cause similar neuron activity to occur. In both cases, the V5 region of their visual cortex showed distinctive activity, suggesting this area is home to the motion-prediction capabilities that allow us to track fast-moving objects.
Previously, in another study, the same team had zeroed in on the V5 region by using transcranial magnetic stimulation (which interferes with brain activity) to disrupt the area and found that participants were less effective at predicting the movement of objects. “Now not only can we see the outcome of prediction in area V5, but we can also show that it is causally involved in enabling us to see objects accurately in predicted positions,” Maus said.
It’s not much of a leap to suppose that this prediction mechanism is more sophisticated in some people than others—which is why most of us would whiff when trying to hit the fastball of a major league pitcher.
A failure in this mechanism might be at work, the researchers say, in people who have motion perception disorders such as akinetopsia, which leaves the ability to see stationary objects completely intact but renders a person essentially blind to anything in motion. Better understanding how neurological activity in the V5 region—along with other areas of the brain—allows us to track and predict movement could, in the long-term, help us develop treatments for these sorts of disorders.
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