Eye tracking reveals how elite baseball players reach peak visual performance

Research Digest

Doran Amos, Neil M. Thomas, Kai Dierkes

June 1, 2021

Participant wearing experimental equipment. The eye-tracker is equipped with eye cameras (for recording images of eyes) and a scene camera (for recording participants' view). The helmet is attached with reflective markers for motion capture. The helmet is tightly fixed to the participant's head with chin strap and headband.

How baseball pushes elite players to their speed limits

Baseball is one of the fastest sports on earth. In top-level professional games, batters must hit the ball less than half a second after it leaves the pitcher’s hand. It’s a sport that tests the very limits of athletic performance, with the ball pitched so fast in professional games that it’s impossible for the batter to track it during the final part of its flight. Even within elite leagues, most batters are unable to hit more than 30% of pitches.

However, a select few of the very best do beat the 30% threshold—what is the secret to their success? How do these masters of the sport hit a ball that’s travelling too fast to even follow with their eyes or head just before it reaches their bat? Researchers from the lab of Prof. Makio Kashino at the NTT Communication Science Laboratories in Tokyo, Japan collaborated with some of the world’s top baseball players to investigate the secrets behind their batting success.

Tracking eye, head, bat and ball movements simultaneously at high speed

Unlike previous sport studies that compared amateur and elite players, all of the participants chosen for the study were elite players from Japan’s top baseball league, the Nippon Professional Baseball (NPB) league. Of the six participants, three were from top NPB teams, while the other three came from lower-ranking NPB “farm teams”.

To understand the gap in batting performance between top and farm players, the researchers used a high-speed, multi-device recording setup to tease apart differences in batters’ eye and head movements, along with those of the bat and ball, on the order of tens of milliseconds. Players wore a Pupil Core headset to track their eye movements, including rapid point-to-point jumps of eye gaze known as saccades, which have been shown to be key to optimal batting (Figure 1). Simultaneously, an optical motion capture system tracked reflective markers attached to the player’s helmet and bat, and a high-speed camera recorded the flight path of the ball.

Figure 1. The researchers combined high-speed eye tracking, motion capture and camera recordings to simultaneously track elite baseball players’ eye and head movements, along with those of the bat and ball, as they fielded balls from professional pitchers.

Top players optimize the timing and accuracy of their eye movements

The researchers found while both top and farm players tracked the ball smoothly during the first 200 ms or so after it was pitched, there was a crucial difference between the two groups in the moments before bat–ball contact. During this time, players made a saccade to the predicted future location of the bat–ball contact to prepare themselves to hit the ball.

Using the high-speed recording setup, the researchers demonstrated that the saccades made by the top players occurred later (around 120 ms before bat–ball contact) and predicted the position of the bat–ball contact more accurately than those made by the farm players (Figure 2).

How did this improve the top players’ batting performance? The researchers suggest that the top players’ later saccades allowed them to keep the ball in their high-resolution foveal vision for longer, leading to a more accurate estimation of the ball’s flight. Amazingly, the 120-ms timing of the saccade in top players closely matches the “physiological time limit” at which motor behaviors such as batting can be adjusted on-the-fly.

Figure 2. Top players (left) made predictive saccades (rapid point-to-point eye movements) later prior to bat–ball contact (0 ms) than farm players (right). Both top and farm players initially tracked the ball with their head, before making predictive saccades. As well as being initiated later, saccades made by top players more accurately predicted the position of the bat–ball contact than those of farm players.

High-speed eye tracking reveals athletic performance at its peak

By combining Pupil Core eye tracking with high-speed optical motion capture and camera recording under highly dynamic conditions, Prof. Kashino and his team successfully showed the precise sequence of eye and head movements used by the world’s top baseball players to reach the very peak of athletic performance. Their study offers intriguing insights into how visuomotor behaviors support elite sporting performance at the highest level, and we at Pupil Labs are glad that our products could contribute to this achievement.

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Copyright: All figures reproduced from the original research article published in Frontiers in Sports and Active Living under the Commons Attribution License (Attribution 4.0 International CC BY 4.0). Copyright holders: © 2020 Kishita*, Ueda and Kashino. *papap6321@gmail.com. Figures cropped and resized for formatting purposes and captions changed to align with the present article’s content.