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Comment by justinclift | Hacker News Reader

Yeah. I've been able to do this for years. Not immediately, but with some concentration and focus when standing in front of a mirror. Works probably 75-80% of the time.

So, "impossible feat"... how would they even think that?

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If it takes time and is not wholly reliable, it sounds like you might be using one of the "indirect methods" they mentioned in the article.

I can change the focal point of my eyes on command to a far away point or a close one, and I have noticed that this reliably makes my pupil get slightly larger or smaller.

Yeah, the article mentions that as the early way the man learned to do it, before being able to directly control the muscle.

That's neat. I wonder if the pupil is actually changing size, or if it's the changing shape of the lens that is making it appear so. If you look into a camera lens as the focus is changed, the inner parts of the camera do appear to change size.

The eye's lens is behind the iris (unlike a camera which is typically the other way around), so the optics shouldn't affect the apparent pupil size.

Whoa. I had no idea. Thanks for informing me! That's so weird. I had always assumed that the curved front surface of the eye was the lens.

You're not wrong - the cornea (front of the eye) has about 3x the refractive power of the lens. Both function as converging lenses, and the only difference is that the refractive power of the lens can be changed.

...until age 45 to 50ish, when the lens hardens into a focus close to infinity and you start to need reading glasses. (presbyopia)

It's the accommodation reflex [0] at work here - pupillary constriction goes hand in hand with a shortening of the focal length of the lens, and the eyes also converge together. This is a brainstem level response, so I doubt there'd be any easy way to dissociate these movements consciously.

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

Interesting, this makes sense. Thanks for figuring it out

This guy can “tremble” his pupil. It’s not the same at all.

I knew a dozen kids in middle school who would do that. I got to the point I can do it sometimes.

I recently discovered / figured this out as well, while practicing meditation. I have found it's a great way to relax my eyes periodically while staring at a screen.

Still can't move my eyebrows independently though.

It sounds similar to how I learned to move my toes independently. It's harder than you'd think and takes a lot of focus. I don't think it's indirect control.

Nope. They only thing I focus on when doing that is changing the pupil size.

Similarly, I can stop hiccups mentally. It's just a little trick of concentration while focusing on the right thing.

I hadn’t heard of this being an impossible feat before and I likewise don’t see why it would be. I remember from Kahneman’s work on human biases and fast/slow thinking that they used pupil dilation as a great proxy for how much conscious concentration someone is using. So I don’t see why controlling it would be such an impossible thing.

First line of the paper:

> Direct control of the pupillary musculature is deemed impossible (Loewenfeld, 1993).

Also, from the abstract, they tested to rule out "increases in arousal by increased mental effort". This is a different phenomenon than what you are discussing.

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