5 ms·

> For example, a professional tennis player can follow the trajectory of a tennis ball after it is served at a speed as high as 160 miles per hour, move to the

> For example, a professional tennis player can follow the trajectory of a tennis ball after it is served at a speed as high as 160 miles per hour, move to the optimal spot on the court, position his or her arm, and swing the racket to return the ball in the opponent’s court, all within a few hundred milliseconds. 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.

nh23423fefe 4y ago
I disagree, and think it would nearly never be hit. Servers use false movement to disguise the serve.
- nitwit005 4y ago
  They do, but within limits. You can't make any random movement and hit the ball somewhere useful. The existence of feints is why I knew people were using the body motions as a strong signal in the first place.
  - okwubodu 4y ago
    This is most obvious in soccer and basketball where you’ll see two similarly skilled players almost get stuck in place trying to predict the other’s next move.
- mulvya 4y ago
  Well, Ronaldo could hit a soccer ball after lights are cut. https://www.youtube.com/watch?v=aoScYO2osb0 https://www.youtube.com/watch?v=aoScYO2osb0
  - nh23423fefe 4y ago
    close but not really. the lights were on at the kick. he couldn't make contact with an invisible ball
- jerojero 4y ago
  There was an experiment done on training for basketball players where a group was told to train for a couple of weeks 3 point shoots. 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).
mseepgood 4y ago
> For example, a professional tennis player can follow the trajectory of a tennis ball after it is served at a speed as high as 160 miles per hour, move to the optimal spot on the court, position his or her arm, and swing the racket to return the ball in the opponent’s court, all within a few hundred milliseconds. This doesn't seem to be specific to the human brain. My cat is probably quicker.
- mlyle 4y ago
  Sure. The point is, biological brains are quite good at this compared to machines, despite it being a composition of trivial mechanics and kinematics problems, and a vision problem that is similar to ones that computers are pretty good at. We seem to do better at it and in a fraction of the power budget of computing.
  - cgrealy 4y ago
    Let's say you're building a robot tennis player. Ignoring the physical engineering for a second, let's assume it can move around and swing a racket with roughly the same speed as a human. 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.
    - mlyle 4y ago
      > 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.
alephxyz 4y ago
That doesn't make it any less impressive
austinjp 4y ago
Agreed! 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.
- Teever 4y ago
  I don't think that returning a tennis serve is a literal reflex as you're claiming. 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.
  - austinjp 4y ago
    My post isn't clear, in that case. I'm not claiming it's a literal reflex :) 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+human+sport https://pubmed.ncbi.nlm.nih.gov/?term=%22motor+primitives%22...

nh23423fefe 4y ago

I disagree, and think it would nearly never be hit. Servers use false movement to disguise the serve.

nitwit005 4y ago
They do, but within limits. You can't make any random movement and hit the ball somewhere useful. The existence of feints is why I knew people were using the body motions as a strong signal in the first place.
- okwubodu 4y ago
  This is most obvious in soccer and basketball where you’ll see two similarly skilled players almost get stuck in place trying to predict the other’s next move.
mulvya 4y ago
Well, Ronaldo could hit a soccer ball after lights are cut. https://www.youtube.com/watch?v=aoScYO2osb0 https://www.youtube.com/watch?v=aoScYO2osb0
- nh23423fefe 4y ago
  close but not really. the lights were on at the kick. he couldn't make contact with an invisible ball
jerojero 4y ago
There was an experiment done on training for basketball players where a group was told to train for a couple of weeks 3 point shoots. 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).

mseepgood 4y ago

> For example, a professional tennis player can follow the trajectory of a tennis ball after it is served at a speed as high as 160 miles per hour, move to the optimal spot on the court, position his or her arm, and swing the racket to return the ball in the opponent’s court, all within a few hundred milliseconds. This doesn't seem to be specific to the human brain. My cat is probably quicker.

mlyle 4y ago
Sure. The point is, biological brains are quite good at this compared to machines, despite it being a composition of trivial mechanics and kinematics problems, and a vision problem that is similar to ones that computers are pretty good at. We seem to do better at it and in a fraction of the power budget of computing.
- cgrealy 4y ago
  Let's say you're building a robot tennis player. Ignoring the physical engineering for a second, let's assume it can move around and swing a racket with roughly the same speed as a human. 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.
  - mlyle 4y ago
    > 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.

alephxyz 4y ago

That doesn't make it any less impressive

austinjp 4y ago

Agreed! 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.

Teever 4y ago
I don't think that returning a tennis serve is a literal reflex as you're claiming. 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.
- austinjp 4y ago
  My post isn't clear, in that case. I'm not claiming it's a literal reflex :) 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+human+sport https://pubmed.ncbi.nlm.nih.gov/?term=%22motor+primitives%22...