You go to the grocery store to pick up your weekly supply of Red Bull and Febreze, but you quickly realize that something is a little off. Specifically, all of the products you pick up scream and fight back when you try to shove them into your cart. Worse, when you finally get to the register, a potted fern asks if you're paying by cash or charge.
"Hey, asshole, my fronds are up here."
Visual agnosia is caused by a dysfunction in some of the brain's visual processing areas, the result of which is that you're unable to correctly identify things for what they are. And we're not talking about confusing a dog with a cat from a distance; we're talking about looking at your brother and trying to cram bread into his hair because you think he's the toaster.
If you think we made up that example to be funny, the neurologist Oliver Sacks described a patient in the book The Man Who Mistook His Wife for a Hat who, at the end of an interview, grabbed his wife's head and tried to put it on his own head. According to the wife, this was the kind of bullshit she had to put up with every day.
"Sick bastard just walked up and started dry-humpin' my head."
People suffering from visual agnosia are stuck seeing the world kind of the way a space rover on Mars does. When a person with a normally functioning brain looks at something familiar, like a rose, she sees a bunch of shapes and colors and her brain automatically tells her what that thing is. The process is so lightning fast that you aren't even aware of it.
But it is a process and it can break down. Agnosia sufferers are permanently trapped in the shapes-and-colors stage. Sacks' patient looked at a rose and described it literally as "a convoluted red form with a linear green attachment." It's kind of like being blind, except you have some jackass following you around describing things to you and making you figure out what those things are on your own. For the rest of your life.
"Convoluted red form with a linear green attachment ... Rose McGowan?"
Mercifully, visual agnosia is just that -- a visual disorder. Sufferers retain the ability to identify things by using their other senses. Sacks' patient was able to recognize the rose when he smelled it.
Pause here and take a moment to thank your brain for all of the shit it does in the background just so you can get around every day.
"I sure hope none of those convoluted gray shapes are people!"
You sit down in the morning to a cup of coffee, and to work the maze on the back of the Lucky Charms box. Your nose itches, and suddenly somebody else reaches over to scratch it.
Then this person grabs your coffee mug and brings it to your lips. You're starting to wonder who this is and why he's being so helpful, considering that you live alone. It's then that you realize, to your horror, that you've actually had someone else's arm grafted onto your shoulder and the goddamn thing is acting all innocent about it.
And the thing is really good with kids, too!
People with somatoparaphrenia suffer damage to the brain's homunculus region or "body map." That's the part of your brain that catalogs all the parts of your body and keeps track of them so you know where all your limbs are without actually looking at them. If you have a stroke or something that messes with your brain, however, it can actually lose track of one of your limbs. And this really, really messes with your head. It makes it so that you can still move the limb and still register feeling -- you just don't recognize it as yours.
In one documented case, a man denied ownership of an arm and a foot, and while he didn't know where the foot came from (it was a "big foot only suited for work"), he figured for some reason that the arm belonged to a woman he knew named Maria.
She did have some guns, though.
In some cases, the experience of having someone else's body parts attached to you is so stressful that people will actually try to get the foreign limbs chopped off. In 1997, a man approached surgeon Robert Smith and asked him to amputate his left leg, which he believed wasn't his. Apparently shooting for the title of World's Most Unethical Surgeon, Smith granted the request, and was immediately swamped by people wanting him to cut off their alien limbs. He actually made a decent living cutting off people's healthy body parts until the hospital ordered him to stop, for some reason.
"Yeah, that feels much better. Thanks, Doc."