the fluidity of perception

I always used to think of the brain’s relationship with reality as fairly concrete. If you see a house, I also see a house. Or even if I don’t — if my vision or my brain has some abnormality that prevents me from seeing the same house as you do — I still know, if you tell me, that it’s a house, and what it should look like.

Then, last fall, I took a neuroscience course, and that put paid to that.

Because there are people out there — people with perfectly normal sensory, motor, and analytical abilities — who simply don’t comprehend the same house I do. If you give them a sketch of a house and ask them to copy it, this is what they draw:

These are people with contralateral neglect syndrome, which isn’t a problem with the brain’s input or output mechanisms but rather a problem with the link between them; it’s a deficit in attention, “an inability to attend to objects, or even one’s own body, in a portion of space”. It happens when one side of a patient’s parietal lobe has suffered an injury. Since each side of the brain generally controls the opposite side of the body, someone with an injury to the right parietal lobe wouldn’t be able to pay attention to things to his or her left, as seen above.

The scientist who first described the condition (whose name, incidentally, was Brain) described several other symptoms, including the feeling that one’s limbs on one side are absent or the inability to navigate between rooms in a house due to a propensity to turn right instead of left. (Patients with this difficulty could give perfectly clear directions — they just couldn’t follow them.)

I don’t know about you, but it blows my mind just a little that I could be otherwise fully aware and in possession of my own will and still be unable to turn left.

Image and W.R. Brain quote from Purves et al.’s Neuroscience textbook, fourth edition.