Is the motion that we see real, or just an illusion?
When you think of the greatest baseball pitchers ever, William Arthur “Candy” Cummings probably doesn’t come to mind, but it should. Cummings, who played for several early major league teams in the 1870s, reportedly was the first to effectively utilize the curveball, a pitch that seems suddenly to drop sharply as it approaches the plate—often leaving the batter swinging at nothing but air. Since then, many generations of curveball pitchers have flummoxed the opposition with their skill and making the ball seem to dance out of reach at the last instant. And for just as long, there’s been a controversy. Does a curveball really curve, or is the movement of the ball just an optical illusion?
Actually, both explanations are true, according to a 2010 article in the scientific journal PLoS ONE by perception researchers Arthur Shapiro of American University and the University of Southern California’s Zhong-Lin Lu. The curveball does curve, but its parabolic path is much more gradual and smooth than the sharp break that the batter thinks he is seeing. The problem is the batter’s eyes. As the ball leaves the pitcher’s hand 60 feet away, the batter tracks
it with his foveal vision—the narrow, high-definition view from a tiny portion of the retina called the fovea. But as the ball arcs and moves toward the edge of the batter's field of view, he switches to using peripheral vision—the fuzzier, but more motion-sensitive, sight produced by the outer retina. Then, as the ball arcs inward toward the plate, at the last moment the batter switches back to using his central vision. The problem: the contrast between the two types of vision creates the illusion that the ball is breaking downward by as much as a foot. As University of Arizona psychologist Rob Gray, who was not involved in the study, explained to the Associated Press: "We tell players to keep their eye on the ball, but you just can't. It is physically impossible to follow a major league baseball all the way to the plate."
The compensatory tactics used by our eyes and brains also mean that they can be tricked into seeing things that aren't really happening. Our brains trick us into thinking that TV
programs and movies—which actually amount to a rapid succession of still images—are actual movement. And we're easily fooled by other illusions, such as the famous "rotating snakes" drawing (see the illusion below!), in which snakes appear to writhe. A recent study, published in Journal of Neuroscience in 2012, suggests that a combination of saccades and eye-blinking tricks our brains. The researchers found a high incidence of those activities while subjects saw the snakes moving. When the subjects' eyes were stable, in contrast, the snakes stopped moving.
One reason it's so easy to fool us is that we can't help but look at anything that's moving. Evolution hard-wired humans to notice rapid movement and pay attention to it, by giving us motion-sensitive neurons called M cells in the retina of the eye. Whenever something moves in our visual field, the M cells start firing impulses along a special pathway to the part of the visual cortex called the MT, which specializes in
processing movement. The urge to look at movement, called the orientating response, probably helped cavemen to hunt while avoiding being eaten by bigger animals. Today, it makes our eyes automatically zoom in on the ballgame or reality show on the TV set when we walk into someone's home. But our ancestors' brains had a simpler job. Back then, "most things moved in simple straight lines at relatively slower speed," Shapiro explains. "It wasn't hard for primitive
man to follow the path of an enemy or prey. Today, society is omni-directional and fast paced."
But even though we're made to pay attention to motion, we're limited in how well we see it. Our eyes move all the time, in tiny fast movements called saccades that occur as often as three times each second. We even have saccades when we're reading a line of text. They last anywhere from 0.02 to 0.2 seconds, and during that time, as our eyes jump and then refocus, our vision blurs. We would find that pretty disorienting, so our brains just edit out the blurs, a phenomenon called saccadic masking. That gives us the illusion that we're looking at a continuous movie of reality, rather than a series of really quick snapshots.
But even with the illusion created by saccadic masking, our brains have to deal with another problem. Every time our gaze shifts slightly, all the details in the next image would need to
be aligned perfectly with the details in the previous image, or else reality would seem hopelessly herky-jerky. In order to avoid all that painstaking work, our brains employ a shortcut called selective attention, in which they only process a small sliver of the visual environment from each snapshot.
Our brains also utilize—and compensate for—other types of eye movement to create the illusory version of reality that we see. Vergence eye movements, in which our gaze rapidly shifts back and forth between distant and close-up objects, enable our eyes to work together and perceive the world in three dimensions. Even when we try to stare at a stationary object for more than a few seconds, an activity called maintained fixation, researchers have discovered that our eyes actually move back and forth slightly. Again, our brains filter out the moments when our eyes slip out of focus, so that we don’t notice it. We also compensate for the eye movement by moving our heads.
When tracking an object moving through space, as baseball hitters have discovered to their frustration, our eyes and brains have an even bigger challenge. When the object is moving in a straight path, they do a pretty good job at what perception researchers call smooth pursuit; our eye movements actually can attain velocities almost equal to that of the moving object that they're watching. But when our visual target is moving in a complex trajectory—think of a
buzzing house fly, for example—our eyes and brains have a lot more trouble, because it takes too much time for them to detect and respond to changes in the object’s path. Our brains ingeniously compensate for the processing delays by making educated guesses about where the object is headed, based upon other information that they pick up from our surroundings. That can work pretty well, especially if you have the fine-tuned oculomotor abilities of NBA star Blake Griffin, who can deftly calculate the angle of a ball caroming off a glass backboard, so that he can catch it and slam it back down into the hoop. But even he probably has a much tougher time swatting a fly, which utilizes random, unpredictable motion patterns as an evasive tactic.
The compensatory tactics used by our eyes and brains also mean that they can be tricked into seeing things that aren't really happening. Our brains trick us into thinking that TV programs and movies—which actually amount to a rapid
succession of still images—are actual movement. And we’re easily fooled by other illusions, such as the famous "rotating snakes" drawing (scroll down the page to see below!), in which snakes appear to writhe. A recent study, published in Journal of Neuroscience in 2012, suggests that a combination of saccades and eye-blinking tricks our brains. The researchers found a high incidence of those activities while subjects saw the snakes moving. When the subjects' eyes were stable, in contrast, the snakes stopped moving.
- Formula Rossa, Abu Dhabi
- Dodonapa, Japan
- Top Thrill Dragster, USA
- Kingda Ka, USA
- Tower of Terror II, Australia
- 1Formula Rossa, Abu Dhabi
- 2Kingda Ka, USA
- 3Top Thrill Dragster, USA
- 4Dodonapa, Japan
- 5Tower of Terror II, Australia
Which of these purple arrows appears to be plummeting
downward at an incredible speed?
Learn to track curveballs like a professional.
As the article above explains, hitting a curveball is one of the most difficult visual feats in sports, because batters are forced to switch back and forth between super-sharp foveal (central) vision and peripheral vision, which is fuzzier but better at detecting motion. The shifting creates the illusion that the ball is breaking downward at the last instant by as much as a foot, which often causes batters to swing at empty air as the ball whizzes by them into the catcher’s mitt. Curveballs are difficult to handle, even for a superstar such as the Los Angeles Angels’ Albert Pujols, one of the most feared hitters in baseball. From 2006 to 2011, according to an article in USA Today, Pujols hit .351 when he was thrown fastball pitches, his average dropped to .275 against
curveballs. He averaged a home run for each 11.9 fastballs he saw, but only hit one out of every 33.3 curveballs out of the park.
But difficult doesn't mean impossible—major leaguers do manage to hit curveball pitching. Baseball and sports vision experts say that training your eyes and brain is an important part of success at the plate. Here are few tips.
1. Know what to look for. You don’t have much time to make a decision at the plate—from the time the ball leaves the pitcher’s hand, you’ve got less than half of a second to decide whether to swing at a pitch and where to swing, experts say. So you’ve got to be able to almost instantly identify a curveball. One way to do this is to train your eyes and brain to focus upon the rotation of the seams on the ball. A curveball has topspin, so it rotates downward.
2. Improve your detail-tracking ability. A 2013 study found that baseball players did about the same as non-players at perceiving moving images, but that they were significantly better at discerning the details of moving objects. That skill, called dynamic visual acuity, helps give a hitter a reference point that makes it easier to track a moving object. Fortunately, it’s a skill that can be improved through practice. One optometry website suggests that you cut out letters, stick them to an old-fashioned record turntable, and try to identify the letters at different speeds.
3. Train yourself to expect the unexpected. Baseball coaches traditionally tell hitters that they need to avoid over-thinking at the plate, because if they’re fixated on the idea that a pitcher will throw a particular pitch in a certain situation, they’re all the more vulnerable to being fooled. Research has shown that the best way to practice hitting is to start with "blocked" practice, in which a batting-practice pitcher
throws a set number of fastballs, followed by a set number of curves, and so on. The repetition enables your brain to forge new pathways between neurons that help you to detect the speed, height, direction, velocity and rate of change in the ball's flight path. Once you develop proficiency, introduce “variable” practice, in which the pitcher throws a random assortment of pitches. That will train your brain to switch gears quickly and adjust to whatever is thrown at you.