When Serena Williams returns a lightning-quick tennis serve—most of us marvel at her skill and speed. Considering what the human brain overcomes to make it happen, these kinds of feats are nothing short of miraculous.
When we watch a moving object, such as a fly, we experience it in the present. But delays in how the brain processes the image from the eye means our awareness of visual events lags behind their occurrence.
So to make it possible to swat a fly or catch a moving ball, the brain has developed a way to overcome this lag. This means we are unaware of this delay and can interact with even rapidly moving objects extremely efficiently.
Researchers investigated this phenomenon and found that the delay with which people make eye movements to a target predicts where they perceive the target, and some people do this better than others.
Hinze Hogendoorn, senior research fellow in the School of Psychological Science at the University of Melbourne, says the brain then works out what the target will do next.
“The cool thing about that is that the brain apparently ‘knows’ how long the eye movement is going to take, uses that to calculate in which direction to send the eye movement, and also uses that same signal to tell awareness where the object is in the first place,” Hogendoorn explains.
“So, it’s a reversal of the intuitive notion that we make eye movements to the place where we see the target. Instead, the eye movement that we are going to make determines where we see the target to which we are making the eye movement,” he says.
“When objects such as flies move unpredictably and we still extrapolate their locations, we end up seeing them in places where they never were.”
‘Predicting the present’
The paper, which appears in the Journal of Neuroscience, looks at transmission delays in the nervous system that pose challenges for pinpointing moving objects due to the brain’s reliance on outdated information to determine their position.
“Acting effectively in the present requires that the brain compensates not only for the time lost in the transmission and processing of sensory information, but also for the expected time that will be spent preparing and executing motor programs,” the authors write. “Failure to account for these delays will result in the mis-localization and mistargeting of moving objects.”
Participants in the study had to indicate the perceived position of a moving ring-shaped target with a computer mouse. Black and white segments continued moving but changed gradually to uniform dark grey.
Researchers asked the observers to start moving the mouse as soon as the target was fully grey.
Researchers found that the visual system uses the spatial and temporal characteristics of an upcoming rapid-eye movement to localize visual objects for action and perception.
“This counterintuitive finding is important because it not only shows that motion extrapolation mechanisms work to reduce the behavioral impact of neural transmission delays in the human brain, but also that these mechanisms are closely matched in the perceptual and oculomotor systems—these are interconnected regions throughout the central nervous system that interact to control various eye movements,” says Hogendoorn.
“One explanation is that the brain overcomes its own delays through prediction. By using what it knows about how objects move in the world, the brain can work ahead to compensate for known delays, essentially predicting the present,” he explains.
In visual motion, the future position of a moving object can be extrapolated based on previous samples. The team recently demonstrated that these neural mechanisms do indeed reduce the lag with which the brain represents the position of a moving object.
“A rapidly moving ball, which you would miss if the brain did not compensate for processing delays, can be caught because its future location can be extrapolated given enough information about its past trajectory,” Hogendoorn says.
“Accurately catching the moving ball further requires that the brain compensates, not only for the delays inherent in the processing of the incoming visual information, but also for the additional delays incurred by the planning and execution of the hand and arm movement,” he explains.
“Effectively functioning in the present requires a predictive mechanism that accurately works out the time lost in transmission and processing of that sensory information,” says Hogendoorn. “As well as the expected time that will be lost in preparing for the next motor program, transmitting the associated motor commands, and actually moving the corresponding effectors—all of that can take up to around half a second.”
“In that time, a fast cricket or tennis ball will have moved more than ten meters. That a person can hit it or catch it—that is pretty amazing.”
‘From perception to action’
Hogendoorn says the findings align with and extend previous research, by showing that motion extrapolation mechanisms are linked to smooth and rapid eye movements.
As for elite sportspeople, he says they could have an inherent ability to process all this information faster and more accurately than others, or develop it through practice. Or maybe both.
“The fact that people are able to do that means that they are very good at extrapolating and predicting where things will be and when,” Hogendoorn says.
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“As an entire system from perception to action, you need to know how long the delay will be along the way.”
So, even though you may not be a world-class athlete, you can still marvel at the sheer computing power of your own brain, the next time you’re trying to catch a ball.
Cheryl Critchey is a freelance writer with a strong interest in psychology, based on Melbourne, Australia. Follow her on Twitter @CherylCritchley
This article originally appeared at Futurity as How our brains predict where speedy objects will go and has been republished here with permission.