You have perhaps been sitting in a car at an intersection, spacing out. The car rolls backward - you're driving a stick, and have accidentally let your foot off the break. Whoah! Better drink some coffee.

Then a bus next to you has rolled away, and you can see your surroundings: you're not moving at all. And very suddenly, it doesn't feel like you're moving anymore either. You thought you were moving, actually felt it, because of the visual cues telling you that you were.

I don't know about you, but a little thing like that can freak me out all day. I remember as a kid scraping up my knees in a bicycle spill, and not feeling anything until I noticed I was bleeding, then screaming out in pain. I always thought it was one of those little kid things, magical thinking or whatever. Not so, I don't think. I have a huge cavity in one of my back teeth, right this second, and it was only after I discovered it that I realized I'd been having toothaches.

In a way it is my expectation that is causing this experience.

So let's agree that very realistic motion/sensory hallucinations can happen (to sane & sober people - I was going to say "unaltered," but that makes us into pets that still need to be neutered, and ruins the eerie effect) quite easily, and that pain can actually be prompted, or at least heightened, by the right visual cues. We all know also that some other physical sensations can be provoked solely by visual cues, and the visual cues need not necessarily be realistic ones. Characters in video games will do, allegedly, for some people. I digress.

Still with me?
I have noticed when I manage to keep the same cell phone for awhile, that my ear is trained to pick out its ring amid a barrage of background noise; that I actually sometimes "hear" the phone ringing in the music I'm listening to, when it's not there. I hear something similar, and my mind fills in the gap. Maybe we can call that a sort of auditory hallucination. Whatever we'll call it, when we take all of this stuff into consideration at once we recognize that what our brains feel it necessary to do is gather bits of information from our environment and leap to conclusions about what those clues mean. What's the point of this, if we can so easily be tricked?

As I think the way to understand something is to dive further into the murk, check this out.

Although a little bit of variation occurs within each square (even unshadowed), square A and square B are the same color. Yes. But you can't see it that way, no matter how hard you try, can you? Neither can I, and I'm a painter. There is this toy at The Exploratorium in San Francisco which consists of two colored squares within two other (differently) colored squares. You have a little rollerball, like you use to move yourself around in the arcade game of Centipede (remember Centipede?) that changes the color of one of the inside squares, and your task is to roll it around until the middle squares match. It's supposed to be difficult: the color of the outer square changes your perception of the inner square. I am exceptionally good at it. I was once sent to get a quart of paint without a color chip, and matched the desired shade of lavender by memory. And I still cannot see that those squares are the same color.

This thing has driven me nuts. I spliced a bit of square A in Photoshop, and moved it to square B. Then I took a piece of square B, and moved it to square A. It appeared to change color as I moved it. Crazy. Should we be unable to do both, it is clearly much more important to recognize something as poorly lit than to recognize what it actually looks like.

This illusion was designed by (as you can see) Edward Adelson, who is (or was) a professor of vision science at MIT. (How cool is that job??)

If you want to play for awhile before moving on, here are some fantastic optical illusions:

When I was new to L.A., I ate lunch at a cafe with a raised wooden patio. Everything trembled. I thought it was a tiny earthquake and, à la L.A. Story, everyone was ignoring it. I've been there enough since to ignore the tremors myself: cars driving by cause them; people walking on the patio cause them. It's just a shaky patio. I ate there a few days ago; a girl at a nearby table was compulsively wiggling her foot, making my whole table shake. My coffee was clinking. Crossword puzzle answers leapt out of bounds. But I knew it wasn't an earthquake. How many times do we have to experience something before we're sure we know what it means? Is the first time we see or feel something the only time? After that, does whatever knowledge we acquired recede into the background, to build the framework within which we position the experience when it happens again? Or has the experience been cached? To save time - especially when threatened - do we simply recall what occurred before, without considering new information at all?

I suppose these sorts of dilemmas drive some people to philosophy.

A philosopher / cognitive scientist, on illusions and consciousness:

In German there is a word, katzefrau. It means cat woman. Also: funktionslust. Function desire, or the joy that comes from being very good at something. In English, we have a word for throwing something out of a window.

And there we go. I retire for the night.

Maybe, like a Hemingway story, what I've said will take shape gradually, after you've put it all away.

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