[jacobolus]

As a parent of small kids who just watched the video, I would say 2–3 year old seems about right, assuming kids who do a lot of running around. 3-year-olds can move with significantly more grace (the motions are more intentional, fluid, subtle, and steady, and seem less scripted) than these robots, but definitely can't do a jump precisely the same 10 times in a row, so it's not really apples to apples.

Maybe age isn't the right measure. I would say that these robots move like a 3-year-old kid who has been practicing a particular motion sporadically for a month or two, but not like an active 3-year old who has been practicing the same motion for a year.

If you compare to the kids who do martial arts or gymnastics or some serious sport or whatever, by age 6 or 7 the kids are leaving these robots in the dust. (The robots are still amazing though.)

[jfengel]

I think your estimate of 6-7 is closer to right. I'm not a parent but as a ballet dancer I get involved in a lot of Nutcrackers, which are showcases for entire schools at all levels.

The 5-and-under crowd just generally swarms around the stage, with little attempt at "dance". The 6-8 year olds are beginning to dance, at about this level -- though I would say I saw a few movements by the robots that were remarkably expressive.

It's a bell curve, and there is certainly a right tail of kids who are far better than these robots at age 6-8. The median, however, is about on par.

[jacobolus]

Oh, there is no way you could get a typical untrained 5 year old to follow this whole choreographed routine.

I am just talking about how smooth and graceful the individual motions are. By age 3 kids who practice something a lot (say, running around barefoot at the playground) are starting to get pretty fluent at it.

The kids have a lot more sensory input, a much more subtle and refined musculoskeletal system with a whole ton of tiny stabilizer muscles, and a pretty impressive neural architecture for learning and refining motions, compared to these robots.

(Which again, is not to criticize the robots, which are also amazing! It is hard to beat 600 million years of animal evolution.)

[jfengel]

I was really impressed at how graceful the machines were.

It's not the first time I've noticed that; drones can also be quite graceful. But the dynamic motion of that pendulum is such a hard problem, and as you note, the three year olds solve it with unconscious ease.

Never as gracefully, and there of course the machines have a huge advantage. I spend most of my brain power keeping the tense muscles very tense and the loose muscles very loose, for each and every one of those tiny stabilizer muscles. The machines move straight and smooth in a way I never will. I haven't mastered the simple art of standing there in first position, and probably never will.

(I am not, I would note, any kind of expert. I dance at the level of an 11 year old. Maybe a 10 year old. Which took me years to learn, and I'm very proud of it.)

[jacobolus]

I have never done any significant amount of dance, so am in no position to offer informed advice, but I wonder if explicitly thinking about every muscle is really the best way to practice. Focusing on higher-level goals and letting the sensorimotor system deal with the details might be more effective (and then figuring out how to observe yourself and deliberately working on correcting specific defects).

You might find the book The Inner Game of Tennis useful.

[jfengel]

It's how I learn. I start with the focus so that I learn the right thing, and then when I have it in muscle memory, I can forget it. And focus on the next thing, while continually checking back in. (The teachers will be sure to correct you if you don't.)

Ballet isn't something that feels right when you do it correctly. It's actually a deeply unnatural way to move. Not just pointe, but everything. The grace is an illusion layered on top of that.

You definitely do need to reach a point where most of it is handled by the sensorimotor system. But there will always be something you need to keep working on.

[OJFord]

Probably need to be more specific about 'skill as a dancer' too though - I think you're responding mainly about motor control (?) but try choregraphing a bunch of three year olds to actually perform that routine!

[bostonpete]

Evaluating robots on whether they do what they're told and whether their timing is good doesn't seem too useful. That's the easy part. Pretty much any robot is going to be more precise/predictable/consistent in their actions than any human, let along a three year-old.

[OJFord]

True, but they've been well-crafted to make them so. Just as they'll (I assume) continue to be worked for finer motor control.