In the two ‘four-eyed’ dogs, messengers of Yama
“GB” is a 28 year old man with a curious condition: his optic nerves are in the wrong place.
Most people have an optic chiasm, a crossroads where half of the signals from each eye cross over the midline, in such a way that each half of the brain gets information from one side of space. GB, however, was born with achiasma – the absence of this crossover. It’s an extremely rare disorder in humans, although it’s more common in some breeds of animals, such as Belgian sheepdogs. […]
In the absence of a left-right crossover, all of the signals from GB’s left eye end up in his left visual cortex, and vice versa. But the question was, how does the brain make sense of it? Normally, remember, each half of the cortex corresponds to half our visual field. But in GB’s brain, each half has to cope with the whole visual field – twice as much space (even though it’s getting no more signals than normal.)
