I've wondered about this too: Here's a few seconds of downhill biking, including my eye movements. How rich is my control of the bike here? Could I execute 1000 (=2^10) different paths over the next second, a million different ones over the next 2 seconds? - ThreadSky

mameister4.bsky.social • 74 days ago

I've wondered about this too: Here's a few seconds of downhill biking, including my eye movements. How rich is my control of the bike here? Could I execute 1000 (=2^10) different paths over the next second, a million different ones over the next 2 seconds?

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selmaan.bsky.social•70 days ago

Is it that there are 1,000 different bike paths, or that you would be capable of doing 1,000 different things? If the latter it seems possible: each place you could choose to look, all the many actions that would have you fall off the bike, do these all count?

tyrellturing.bsky.social•74 days ago

I bet your control of the bike here is well above 10 bits/s.

You've probably got dozens bits alone on the steering angle every 100 ms or so. Then you've got your speed, balance angle, etc. Add in your planning, eye movements, so on...

I bet this behavious is at least thousands of bits/s.

mameister4.bsky.social•74 days ago

That actually sounds like a tall order, and I don't think that level of control is necessary to keep me from falling into the abyss. Obviously we choose our sports so they fit inside our 10 bits/s limitations.

mameister4.bsky.social•74 days ago

A separate issue is what my nervous system does to just execute the pedal strokes that keep the bike going. Lots of moment-to-moment control using sensory feedback driving millions of muscle fibers. All this high-rate processing happens in the spinal cord and brain stem, part of the "outer brain".

neurostats.org•74 days ago

📌

brittonsauerbrei.bsky.social•70 days ago

I think there's also a danger of overestimating the bandwidth on the motor side: multiple muscle fibers supplied by each motoneuron, size-based recruitment of a MN pool typical (though exceptions a significant open question), muscle synergies, etc.

brittonsauerbrei.bsky.social•70 days ago

There are probably implications for the limitations of myoelectric user interfaces, as well (e.g. Meta's), similar to the issues you point out for BCI in the paper. The number of degrees of freedom controllable by the user is << than the number of motor units you can record.

mameister4.bsky.social•74 days ago

Our engineered devices work like this too. Most of a car's sensory-motor processing happens in its spinal cord, like "when to send a spark to cylinder 3 based on current air flow, temperature, and throttle?" The genius of vehicle engineering is that it requires <10 bits/s of input from the driver.

tyrellturing.bsky.social•74 days ago

I largely agree with this, but would push back against the idea that this is all handled by your brain stem/spinal cord.

For example, do you not think that your forebrain is helping you to decide what angle to take for different parts of the path, identifying which objects can be hit safely, etc.?

andpru.bsky.social•70 days ago

At least for the processing of somatosensory signals in primates, feedback control involves a pretty big chunk of cortex including those parts that are typically implicated in generating 'voluntary' motor commands. Same neurons.

brittonsauerbrei.bsky.social•70 days ago

The cerebellum contains around half the neurons in the brain, and does mostly unconscious processing for low-level control. To the extent one can even make a clean “inner” / “outer” division, most of the brain is “outer.”

tyrellturing.bsky.social•74 days ago

And what if you were running the trail? Then the engineered system the gives you a control bottleneck wouldn't be present, and your body has to start dealing with all sorts of additional variables.

mameister4.bsky.social•70 days ago

I do think that, but doubt that it contributes more than 10 bits/s. Recall that means choosing among 1000 different possible trajectories of the bike over the next second. A second is a very short time in that movie clip.

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