How To See A 130 MPH Tennis Serve

For most of us mere mortals, if an object was coming at us at 120-150 mph, we would be lucky to just get out of the way. Players in this week's U.S. Open tennis tournament not only see the ball coming at them with such speed, but plan where they want to place their return shot and swing their racquet in time to make contact. At 125 mph from 78 feet away, that gives them a little less than a half second to accomplish the task.

How do they do it? Well, they're better than you and I, for one. But science has some more specific answers to offer.

Swiss researchers have concluded that expert tennis players, like their own Roger Federer, have an advantage in certain visual perception skills, while UK scientists have shown how trained animals — and presumably humans — can rely on a superior internal model of motion to predict the path of a fast moving object.

For any sport that involves a moving object, athletes must learn the three levels of response for interceptive timing tasks. 

• First, there is a basic reaction, also known as optometric reaction (in other words, see it and get out of the way).

• Next, there is a perceptual reaction, meaning you actually can identify the object coming at you and can put it in some context (for example: That is a tennis ball coming at you and not a bird swooping out of the sky).

• Finally, there is a cognitive reaction, meaning you know what is coming at you and you have a plan of what to do with it (return the ball with top-spin down the right line).

This cognitive skill is usually sport-specific and learned over years of tactical training. Obviously, professional tennis players are at the expert cognitive stage and have a plan for most shots.

But, in order to reach that cognitive stage, they first need to have excellent optometric and perceptual skills.

Leila Overney and her team at the Brain Mind Institute of Ecole Polytechnique Federale de Lausanne (EPFL) studied whether expert tennis players have better visual perception abilities than other athletes and non-tennis players. Typically, motor skill research compares experts to non-experts and tries to deduce what the experts are doing differently to excel.

They carried out seven visual tests, covering a wide range of perceptual functions including motion and temporal processing, object detection and attention, each requiring the participants to push buttons based on their responses to the computer-based tasks and each related to a particular aspect of visual perception.

In this study, which was detailed in the journal PLOS One, Overney wanted to see if the perceptual skills of the tennis players were not only more advanced than non-tennis players but also other athletes of a similar fitness level, (in this case triathletes), to eliminate any benefits of just being in top physical shape.  To eliminate the cognitive knowledge difference between the groups, she used seven non-sport specific visual tests which measured different forms of perception including motion and temporal processing, object detection and attention. The participants watched the objects on computer screens and pushed buttons per the specific test instructions.

The tennis players showed significant advantages in the speed discrimination and motion detection tests, while they were no better in the other categories.

"Our results suggest that speed processing and temporal processing is often faster and more accurate in tennis players," Overney writes. They even scored better then their peers, the triathletes. "This is precisely why we added the group of triathletes as controls because they train as hard as tennis players but have lower visual processing demands in their sport."

Still, are the tennis players really just relying on their visual advantage when given that half second to react? Have their years of practice created an internal cognitive model that anticipates and predicts the path of an object?

Nadia Cerminara worked on that question. Cerminara, of the University of Bristol (UK), designed an experiment that taught household cats to reach with their paw at a moving target. If they successfully touched the target, they received a food reward.

After training the cats to be successful, she recorded their neuronal activity in their lateral cerebellum. Then, she measured the activity again but would block the vision of the cats for 200-300 milliseconds while performing the task. Despite the lapse in visual information, the neuron firing activity remained the same as before. Cerminara concluded that an internal model had been used to bridge the gap and provide a prediction of where the object was headed.

The study was published in the Journal of Physiology.

So, when faced with a blistering serve, science suggests that players like Federer not only rely on their superior perceptual skills, but also have created an even faster internal simulation of a ball's flight that can help position them for a winning return.

Of course, you may want to avoid the world's fastest server, Andy Roddick, especially when he's upset from a bad line call (see video). :-)

Brains Over Brawn In Sports

Sometimes, during my daily browsing of the Web for news and interesting angles on the sport science world, I get lucky and hit a home run.  I stumbled on this great May 2007 Wired article by Jennifer Kahn, Wayne Gretzky-Style 'Field Sense' May Be Teachable.  It ties together the people and themes of my last three posts, focusing on the concept of perception in sports.


Wayne Gretzky is often held up as the ultimate example of an athlete with average physical stature, who used his cognitive and perceptual skills to beat opponents.  Joining Gretzky in the "brains over brawn" Hall of Fame would be pitcher Greg Maddux, NBA guard Steve Nash and quarterback Joe Montana.  They were all told as teenagers that they didn't have the size to succeed in college or the pros, but they countered this by becoming master students of the game, constantly searching for visual cues that would give them the advantage of a fraction of second or the element of surprise.



Kahn's story focuses on two sport scientists that we have met before.  Peter Vint, sport technologist with the US Olympic team, who I highlighted in the post, Winning Olympic Gold With Sport Science,  comments on this, "In any sport, you come across these players.  They're not always the most physically talented, but they're by far the best. The way they see things that nobody else sees — it can seem almost supernatural. But I'm a scientist, so I want to know how the magic works."  So, Vint and his team continue to search not only for the secret to the magic, but how it can be taught.



Vint acknowledges the work of one of his fellow sport scientists, Damian Farrow, of the Australian Institute for Sport, who was part of the discussion roundtable mentioned in my post, Getting Sport Science Out Of The Lab And Onto The Field.


He is also fascinated with the perceptual abilities of elite athletes.  In his own sport, tennis, he wanted to know how expert players could return serves much better than novice players.  Similar to the research we looked at in an earlier post about tennis, Federer and Nadal Can See the Difference, Farrow designed an experiment that would try to identify the cues that players might need to instinctively estimate the speed and direction of a serve.  He had three groups of players, expert, non-expert but coached, and non-expert/non-coaced novices, wear ear plugs to block out the sound of the ball hitting the racquet as well as occlusion glasses that could block vision with the touch of an assistant's button.  

By changing the point of the serve at which the glasses would go black, and the players would be "blind", he could try to isolate the action of the server that the expert players might be tuned into that the novices were not.  The decisive point was immediately before impact between the racquet and the ball.  Arm and racquet position at that point seemed to let the expert players estimate the direction of the serve more accurately than the novices.


But Vint and Farrow are not satisfied just knowing what an expert knows.  They want to understand how to teach this skill to novices.  From his own competitive tennis playing days, Farrow remembers that if he consciously focused his mind on things like arm position, racquet angle, etc., he would be miss the serve as his reaction time would drop.  He understood that players need to not only learn the cues, but learn them to the point of "automaticity" through implicit learning.  

You may remember our discussion of implicit learning from the post, Teaching Tactics and Techniques in Sports.   Malcolm Gladwell, in his best-selling book, Blink, calls this implicit decision-making ability "thin slicing" and gives examples of how we can often make better decisions in the "blink" of an eye, rather than through long analysis.  Obviously, in sports, when only seconds or sub-seconds are allowed for decisions, this blink must be so well-trained that it is at the sub-conscious level.

For Vint and Farrow, the experiments continue, looking at each sport, but beyond the raw physical and technical skills that need to be taught but often times are the only skills that are taught.   

Understanding the cognitive side of the game will provide the edge when all else is equal.

Federer and Nadal Can See the Difference

Watching Roger Federer and Rafael Nadal battle it out in the French Open final and now again in the Wimbledon final, I started thinking more about the interceptive timing task requirements of each of their visuomotor systems... yeah, right. C'mon, I just needed a good opening line for this post.


However, other than a 120 mph tennis serve, take a second to think about all of the different sports that send an object flying at you at very high speeds that you not only have to see, but also estimate the speed of the object, the movement of the object and what you want to do with the object once it gets to you.



Some examples are:
- a hockey puck at a goalie (70-100 mph)
- a baseball pitch at a batter (70-100 mph)
- a soccer ball kicked at a keeper (60-90 mph)


Previously, we took a look at this in baseball and in soccer and also discussed the different types of visual skills in sports. There, we broke it down into three categories:

- Targeting tasks
- Interceptive timing tasks
- Tactical decision making tasks

The second category, interceptive timing tasks, deals with the examples above; stuff coming at you fast and you need to react. There are three levels of response that take an increasing level of brainpower.

First, there is a basic reaction, also known as optometric reaction. In other words, "see it and get out of the way". Next, there is a perceptual reaction, meaning you actually can identify the object coming at you and can put it in some context (i.e. that is a tennis ball coming at you and not a bird swooping out of the sky).

Finally, there is a cognitive reaction, meaning you know what is coming at you and you have a plan of what to do with it (i.e. return the ball with top-spin down the right line). This cognitive skill is usually sport-specific and learned over years of tactical training. Obviously, for professional tennis players, they are at the expert cognitive stage and have a plan for most shots. Federer's problem was that Nadal had better plans.

But, in order to reach that cognitive stage, they first need to have excellent optometric and perceptual skills. Can those skills be trained? Or are the best tennis players born with naturally better abilities? Did their training make them better tennis players or are they better players because of some natural skills?


Leila Overney and her team at the Brain Mind Institute of Ecole Polytechnique Federale de Lausanne (EPFL) recently studied whether expert tennis players have better visual perception abilities than other athletes and non-tennis players. Typically, motor skill research compares experts to non-experts and tries to deduce what the experts are doing differently to excel.

In this study, an additional category was added. Overney wanted to see if the perceptual skills of the tennis players were significantly more advanced than athletes of a similar fitness level, (in this case triathletes), to eliminate the variable of "fitness", and also more advanced than novice tennis players (the typical comparison). To eliminate the cognitive knowledge difference between the groups, she used seven non-sport specific visual tests. Please see the actual study for details of all the tests.

The bottom line of the results was that certain motion detection and speed discrimination skills were better in the tennis players (in other words, being able to track a ball coming at you and its movement side to side).


So, the expert tennis players were better at tracking balls coming at them than triathletes and non-tennis players.... seems pretty obvious(!) But, these results are a first step to answering the question of "can these skills be trained"? We see that there is, indeed, a difference in ability level between expert players and athletes that are in similar shape and competitive spirit. Now, the question becomes, "how did these tennis players acquire a higher level of perception skill"? Was it "nature or nurture", "genetically gifted or trained through practice"?


Source: Overney, L.S., Blanke, O., Herzog, M.H., Burr, D.C. (2008). Enhanced Temporal but Not Attentional Processing in Expert Tennis Players. PLoS ONE, 3(6), e2380. DOI: 10.1371/journal.pone.0002380