3Refusing to See Anything on Your Left
Pretend you're at a strip club. Directly in front of you are two dancers, Big Juan and Jermaine the Beefmaster, doing their thing. While Juan is butt-thrusting on your right side, Jermaine is bending over and jiggling his booty meat on your left. But you only have eyes for Juan, and Jermaine is dead to you. Not because you're not into black guys, because goodness knows you are, but because you've got a case of hemineglect and your brain won't let you see anything on your left.
People with hemineglect are notoriously bad tippers.
Your brain, as you probably know, is divided into a left and a right hemisphere, with one hemisphere processing sensory information received from the opposite side. So if you stub your left toe, it will be the right part of the brain that tells you to scream "Pissing Cooch Bubbles!" and wet your pants. If your right parietal lobe is damaged by a stroke, injury, a brain tumor or lesions, you're not going to process anything you see on the left side of your body. It's not that your left eye doesn't work, it's that your brain can't make the connection to what you're seeing. The picture below shows what happened when a hemineglect patient was asked to copy a picture:
Via Psychology Today
She had to erase the left half because it was too gruesome to show other humans.
She drew half the house and said, "Done. Looks good to me." And that's not even the crazy part. The crazy part is that when asked to finish the picture, patients come up with insane excuses why they can't do it, like "I'm not good at drawing trees" and "The fence will just blow down in the wind."
And not seeing things is only half of the problem -- patients are also known to neglect the left half of their bodies as well. As in they only wash, groom and dress half of their body.
"It'll be fine. I do all of my surgeries one-handed, anyway -- no need to wash it."
Patients have been known to leave half the food on their plate and ignore voices coming from one side of the room, and of course driving would be completely out of the question. Not to mention avoiding any Two-Face-related Batman movies, The Phantom of the Opera and Mel Gibson's dramatic 1993 film The Man Without a Face, which would probably be the greatest hardship of all.
And here is actually one version of this that's even weirder ...
2Only Seeing One Thing at a Time
At any given moment, you're not really seeing everything that's in front of your eyes. For instance, when you watch TV, you're not really aware of the rest of the room, you're only paying attention to what's going on on screen. When you drive, you see the road, not the bird shit on the windshield, even though it's right in your line of vision. Everything else gets filtered out.
Dorsal simultanagnosia is a condition that's sort of like that, except patients can literally only see one thing at a time. If that one thing happens to be the wart developing on your eyelid flap, we're sorry, that's all they can see. They can't help it. Their brains can't process anything more than that. If you point them toward your lips, they'll see your lips, but your eyes will disappear.
"Oh my God, what do I have to do to get you to notice my balls?"
This is due to a failure in another bit of the mental software behind eyesight that we take for granted -- our ability, on the fly, to decode and prioritize what we're seeing, to piece all of it together to make a meaningful narrative in our heads. The people who suffer from dorsal simultanagnosia don't suffer from tunnel vision -- their eyes work fine. There is nothing wrong with their thinking -- their minds are intact. But show them your desk at work and they'll just see a stapler. That stapler could be in the middle of the desert for all they know. The rest of the room could be packed full of people or completely empty. All they see is the stapler.
And now, all they can think of is how much they want to staple you.
This means that if you took them to a new room, they'd have to slowly piece together what's going on, one clue at a time. "A clock on the wall. Well, every room has one of those. A magazine lying on a table. Are we at the library? There are chairs. A pamphlet from a pharmaceutical company ... ah, it's the waiting room at a doctor's office."
Just like everything else on this list, the condition can come from brain trauma, brain lesions or a stroke, but this time the damage hits the spot where your parietal lobe and occipital lobe meet. Diagnosing the condition involves a technique that looks like it comes from a 30-year-old Highlights magazine. Patients are asked to look at the picture below and explain what they see:
"All I see is blind, boiling rage."
If the viewer says "curtains" or "a plate" instead of "those children have a mother who is stoned out of her mind," they probably have this disorder.