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First, consider time and distance. An MLB pitcher’s mound is 60.5 feet from home plate. A ball traveling 100-mph will cover that distance in 375 to 400 milliseconds (ms), less than a half second. A blink is 300 to 400 ms, so if the batter blinks when the pitch is thrown, he may not even see the ball pass him! Next, a flash of light evokes neural activity in the brain with a delay of 30–100 ms, and reaction time to swing the bat is 100-200 ms. Combining the midpoints of those ranges, 65 and 150 respectively, leaves barely a quarter of a second for the batter to determine exactly where the ball is, and that’s if he doesn’t blink. Still, it’s possible to hit 100-mph fastballs. Is it pure luck?
Researchers at the University of Washington School of Medicine may have the answer. The team looked at how motion was processed by cellular circuits in the retina. The circuits the researchers focused on are composed of the light-sensing photoreceptor cones; an intermediate layer of cells, called bipolar cells; and ganglion cells that collect signals from bipolar cells and transmit these signals to the brain. Hundreds of photoreceptor cells connect to dozens of bipolar cells that, in turn, connect to ganglion cells. A single ganglion cell has to extract motion information from these signals and relay that information to brain regions that process motion.
The team analyzed the signals to see if the ganglion cells were generating predictive motion encoding, patterns that reflect information that could be used to predict the future motion of an object. Spikes recorded coming from the ganglion cell in response to a moving object, such as a baseball, enabled researchers to calculate how much information the spikes contain about where the ball is likely to be in the future. To evaluate how effectively the cells were transmitting predictive information, the researchers compared the performance of the ganglion cells to computer programs created to solve this type of problem. They found that the ganglion cells were nearly as effective at transmitting this predictive information as the best performing computer programs.
When a bipolar cell becomes excited by signals from its photoreceptor cells, in addition to sending a signal to the ganglion cell, it stimulates neighboring bipolar cells. If the neighboring cells also receive signals from their photoreceptor cells, they are more likely to send a strong signal to the ganglion cell. In this way, as a moving object passes over the visual field, the information about that movement flows through the network of bipolar cells. The ganglion cell ultimately collects the incoming information from the bipolar cells and encodes it in signals that provide the brain with information about the motion of the object. With information from many thousands of these ganglion cells about the path of the object, the brain can then quickly predict its trajectory.
While you may not be able to keep your eye on a 100-mph fastball, the amazing eye-brain connection can still help you hit it. Just don’t blink!
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