I suspect if you made a perfectly invisible ball, you'd find people would manage to hit it back quite often. There's a lot of signal from the opponent's body motion.
This doesn't seem to be specific to the human brain. My cat is probably quicker.
It doesn't have anything other than a camera to track the ball.
So in terms of it's control, we have two options: 1: track the ball in 3d, work out the velocity, trajectory, ballistics, etc and then calculate the optimal position and swing to return. 2: use some form of ML that recognises patterns and applies patterned responses.
I'm willing to bet that 2 will significantly outperform 1, for a fraction of the compute power (once the training data is done).
Because that's what humans do. No one is working out equations in real time.
Human brains aren't bad at this, but I'd bet large sums of money that machines will out perform us at this within a decade.
I'm not so sure. Many other spaces where computers outperform us come nowhere close to doing it in the same power budget, and the amount of power it takes isn't reducing quickly.
> Because that's what humans do. No one is working out equations in real time.
I believe we do something in-between-- like have a kinematics and tracking engine that is fuzzy and gets tuned/updated/supplemental training for particular problems we face a lot, but isn't very tennis-motion specific.
The equations may be very strange from the point of view of the underlying physics/kinematics problem. There's a lot of representations of the problem that fit well and may map better to what our perceptions see and the level of precision that our muscles need.
And it's likely very messy--- we don't have some clean, nested set of controllers here, but strange ways that many kinds of feedback are combined.
This, of course, shunts the question one level of abstraction away, but the standard evolutionary arms-race handwaving suffices here. So long as one side does it, by random chance or a side effect of sexual selection or whatever, the other side eventually does, too.
What follows is in addition, not in contradiction.
The complexity of human musculoskeletal coordination is astonishing. Particularly in sport, but also in daily life. Consider: how many ways are there to raise a cup to your mouth? Basically: infinite. And yet you do it without a care, almost reflexively, barely paying attention. In sub-second sporting tasks, the role of the conscious brain is likely to be zero, but the role of anything above the brain stem is also often unclear.
The spine - home to reflex action - doesn't have the processing power to determine how to return a tennis serve, yet this sort of action is far quicker than any deliberate, calculated, conscious action.
When I last spent any time reading around the subject, the literature was full of stuff like how the central nervous system updates its expectations based on feedback when trying to achieve a goal; and hints about how musculoskeletal movement might involve "orchestration" of composable units of coordination.
It's a fascinating area of research.
Overlaps with robotics and ML are obvious, although I suspect those approaches are "inventing" rather than "discovering". Nothing inherently wrong with that, of course.
From my understanding a reflexive move requires some sort of stimulus, and there's no way that your spine can have stimulus of an incoming tennis ball unless the eyes and therefore the brain are involved.
A top-flight tennis player is responding extremely quickly, and extremely accurately. Deliberate, planned action is not happening. It's something else. It's not a spinal reflex, it's something that involves parts of the brain to very rapidly 'orchestrate' a highly complex musculoskeletal dance.
The raw processing necessary to coordinate that dance cannot (in my understanding) be achieved by familiar neurological pathways -- observing, planning, deciding, coordinating. The planning and deciding aspects are bypassed. Only a tiny fraction of the observing aspect is used, such as the moment the other player strikes the ball (because the ball then moves too fast to react to). Some form of prediction happens. Then a number of 'movement primitives' seem to be selected and orchestrated. Ideally, the whole system is tweaked in real-time based on feedback (visual, proprioceptive) regarding whether the goal was achieved -- i.e. did you return the serve well.
It's wild.
It's also possible I'm mis-remembering and mis-interpreting some of this stuff :)
Good place to start reading: https://pubmed.ncbi.nlm.nih.gov/?term=%22motor+primitives%22...
The existence of feints is why I knew people were using the body motions as a strong signal in the first place.
One group trained normally, as in, they would position themselves and throw the ball.
Another group trained the same way, except they had no ball. So they had to position themselves and throw an imaginary ball.
A final group was obviously told not to train at all.
The results of this study showed similar progression between the ball group and no ball group and no progression for the no training group. And the study continued on showing that the exercise of repeating the pattern even without the ball strengthened the neural pathways that are usually activated when doing the action. From brain to arm and that a big part of "learning" is not actually adjusting but reinforcing.
So I imagine the players in tennis would definitely be able to hit the ball if they trained without it. At least to a certain point (adjusting is important as well obviously).