Jon Aquino's Mental Garden

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Sunday, April 18, 2010

It is interesting to watch one's pupils dilate and contract

Have you ever seen your pupils expand and contract? It's pretty neat. Go to a mirror and look at your eyes. If you've never looked at your eyes closely, have a look - they're amazing equipment. Anyway, that quarter-inch black dot in the middle is your pupil - it's where light enters your eye. The colored part around it is your iris - it controls the size of the pupil. I have brown eyes, so my iris is brown.

If you cover or partly cover your eyes with your hands, the black dot that is your pupil will get bigger, to allow more light into your eye (since you've made things dark). When you take your hands away, the pupil will shrink back down. This is an automatic response to the amount of light available - I find that I can't control the diameter of my pupils by any kind of mental effort.

It's a pretty sophisticated mechanism.


  • Note that it's also linked to our emotions (or drug use) and that people may interpret it (even unconsciously) as an increased attention.

    On a side note, the slower effect of the rhodopsin is also interesting. It's what allow us to better see in dark after 10 min. A useful trick to use when light level changes, is to close one eye to keep its adaptation to dark.

    By Anonymous Alink, at 4/20/2010 2:50 PM  

  • Interesting - thanks Alink.

    By Blogger Jonathan, at 4/20/2010 4:10 PM  

  • Jonathan you're mad bonkerz. But I'l tell you a little secret, all the best people are. :)

    -Lola Greeneyes

    By Anonymous Anonymous, at 5/05/2010 10:59 PM  

  • Here's something fun to do with a cat and some bubble gum and a light room. Chew the gum. Get the cat to look at you. Make sure the room is light, so the cat's irises are contracted. Blow a bubble. My cat's eyes dilate to nearly full-open instantly when I do this. "Far out!"

    By Anonymous Anonymous, at 7/04/2010 7:16 PM  

  • Ha!

    By Blogger Jonathan, at 7/21/2011 8:26 PM  

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