Even in the dark, brain “sees” its own body’s movement | Hacker News Reader

Even in the dark, brain “sees” its own body’s movement

news.vanderbilt.edu

29 pointsd4vlx7 comments

I've seen this doing the rounds, and I'm a bit surprised by the publicity it's getting. The interpretation of the results is fanciful. The results merely show that a person's report of an event will be biased by their expectations. This can be done with anything. There are more rigorous studies of "efference copy" which are actual signals that are sent out to different parts of the brain indicating that a movement is about to be made. Such efference copies are important for actions involving timing where the proprioceptive feedback from the limbs would arrive too late to be useful (so some brain regions get a predictive signal that allows them to plan further action in time).

They aren't relying strictly on subjective reports, though. They are also doing eye tracking. It'd be more solid if it was backed up by MRI or EEG or some other kind of brain function measurement, but that's something, at least.

I've experienced this effect numerous times (for my whole body, not just my hands), and I always figured it was due to proprioception cross-talking with the geometry-extracting part of visual processing. The result that synaesthetes report more vivid images seems to support something like that. Definitely worth doing neurological studies on to see exactly how it works, but I never realized it was the sort of thing that anybody would be surprised by.

A few years ago, I took a tour of this underground cavern in Northern California. About 50 stories (this may be incorrect) underground with absolutely no natural light coming in.

The tour guide took us to the deepest part, turned of all the lights and told us that this was what being in absolute darkness was like. The tour guide also told us to wave our hands in front of our faces. I thought I saw my own hand in front of me and before I had a chance to comment about that, the tour guide mentioned how if you think you see your hand, you're not.

Glad I came across this. Really helps shine some light (I'm sorry) on what I saw.

I thought there was a word for this: proprioception. The fact that this could bleed into visual perception does not seem surprising. Your brain has a sense of your body's position in space.

I've noticed this effect (based on the title) when I close my eyes in a very dark room. I can sometimes "see" a very faint silhouette of my arms, and sometimes the object they're holding, roughly where they should be if the lights were on, slightly darker than the eigengrau[0]. I've wondered whether part of my brain is generating an "expectance mask" (my made up term) in my visual system.

[0] https://en.wikipedia.org/wiki/Eigengrau

Eigengrau is the color of my Moleskin.

I don't get the difference between 'seeing' my hand, and looking in the direction of where I know my hand to be.

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