“Watch the ball” isn’t as simple as it sounds.
When an object’s motion is sufficiently fast, it’s actually impossible for the eye to smoothly track that object throughout its entire flight path. Instead, the brain must employ a different visual tracking tool – saccades, quick jumps of focus from one fixation to another – in order to track it.
Many of the balls you hit in tennis are just like this – they cross your field of vision too quickly for your eye to follow them with smooth pursuit tracking. As a result, they must be tracked with saccades instead.
In order to hit these balls consistently, you must be content to fixate on the ball only at certain, critical points during its flight. Your eyes need to jump to these fixation points before the ball actually gets to them, thereby giving the image time to stabilize before the ball arrives. Then, as the ball crosses your field of vision, you pick up information about its flight.
Multiple times throughout a fast moving ball’s flight, you’ll execute the same visual pattern:
- Predict a future location of the ball.
- Perform a saccade, fixating there before the ball arrives.
- Hold your gaze on said point until the ball arrives.
- Track the ball briefly through your focus.
Hold your gaze briefly at each fixation, to give the image on your retina time to stabilize. Allow the ball to come into clear focus and then begin crossing your foveal vision, thereby revealing its future flight. You can track the ball for a few degrees, through your focus, without performing another saccade.
Once you have enough information, jump to the next point of interest, and repeat.
This entire tracking loop happens extremely quickly, and it happens multiple times per shot, with each iteration following immediately after the last. You aren’t going to be conscious of every step, and your brain certainly isn’t going to interpret every step with the same words I’ve used to describe the step here. Ultimately, you want this process to become automatic.
Your predictions will get better and better as you track more and more tennis balls. The process might seem complicated when written out in text, but your brain already tracks like this this all the time, without you even noticing. Any time you’ve successfully returned a fast serve, you’ve performed at least one successful predictive saccade, even if you weren’t aware of it.
The Tracking Accuracy Cascade
While tracking a ball, the accuracy (or inaccuracy) of your predictions will cascade: if you saw the ball crystal clearly at your last fixation, you’re more likely to catch it crystal clearly again at the next, and vice versa. Tracking well early in the ball’s flight helps you track better late in the ball’s flight, and perfect tracking late in the ball’s flight all but ensures a clean strike.
Often, you’ll miss a fixation – you try to see the ball crystal clearly as it bounces, and you fail to. Typically, this indicates a deficiency in the previous fixation. Let’s use this common situation – not seeing the ball bounce – as an example of how tracking accuracy cascades.
When you miss the bounce, it means your predictive saccade to the bounce area was inaccurate – either your eyes jumped to the wrong spot, or they got to the right spot, but too late (saccadic masking blocked your view). This likely happened because your previous fixations gathered insufficient visual information to correctly guess the bounce location and time.
Now, because you’ve missed the bounce, you’re also likely to mispredict your contact point’s location and time. You won’t see that well either, and you’ll probably miss your shot.
Tracking Position and Velocity
Good tracking cascades positively. Precise early tracking provides two major benefits later in the tracking process, the first of which we’ve already touched on.
- It allows the brain to accurately predict the location of future points of interest, like the bounce.
- It provides extra position and velocity information which your brain will integrate with later information.
If you feel like you’re seeing the ball clearly, but you’re still mishitting it, chances are you observing the ball’s position correctly, but not its velocity. In order to hit the ball cleanly, we need to know both.
Position: Where is it?
Velocity: Where is it moving? How fast?
Often, a single fixation isn’t enough to answer all of these questions; we need information gathered from multiple fixations, integrated together.
A player might always see the ball clearly just before they hit it, and yet still have severe timing issues. This occurs because, while they always know the ball’s position, insufficient early tracking information leaves them unaware of the ball’s velocity. Once their upstream fixations improve, they will be well aware of both position and velocity at contact, and their timing issues will abate.
Many players have contact mistakes in their game that frequently occur with no apparent cause. Sometimes, it’s clear the player was out of position, or took a wild swing, but other times, everything feels fine and then… the ball just hits the frame.
Almost certainly, it’s because the player missed seeing the ball clearly at one or more critical points along its flight path, and it’s their saccadic tracking that needs to improve. The player either:
a.) predicted the future location of the ball incorrectly, jumping their eyes to the wrong place,
b.) predicted too slowly, getting there, but not in time for the image to stabilize before the ball arrived, or
c.) pulled their gaze away from their fixation before sufficient information was gathered for the next prediction.
These are all issues that take time to practice. Intention is everything with vision. You are trying to see the ball, crystal clearly, at various points along its flight, such that, after the shot, you can remember visual snapshots of those points.
Even though, on a fast ball, you’ll only be able to catch it on the fovea a few times before we have to hit it, by choosing those fixations intelligently, you’ll have plenty of visual information about its position and velocity by the time it arrives in order to strike it consistently.
If, multiple times throughout the ball’s flight, it comes into crystal clear focus, that indicates your predictive saccades are accurate. When this is the case, you will have confidence when you go to strike the ball. You’ll time it well, and you’ll feel free to select from many different shots as you initiate your swing.
This is how players like Roger Federer are able to occasionally strike ridiculous service return winners, on serves that have no business being punished like that. With some good (you could call it lucky) anticipation, Federer is able to catch the ball in perfect focus at many points throughout its flight. As a result, by the time he gets to contact, his brain has an extremely precise idea of where it is, and how its moving, causing him to time it perfectly, and successfully execute even the most difficult of shots.