You might, Egnor thinks, end up seeing double out of an eye a thousand miles away. If you don’t agree, what do you think would happen?
… let’s assume a science fiction scenario — a thought experiment — in which there is an exchange. Jack gets Mary’s right eye/hemisphere and Mary gets Jack’s right eye/hemisphere. Both parties, who live on different parts of the planet, survive. For simplicity, we will focus on Jack’s right eye/hemisphere, which is now literally inside Mary’s head.
Jack’s right eye/hemisphere is surgically connected to Mary’s blood vessels, etc., so it remains alive. But it’s no longer connected with Jack’s body. It also can’t connect with Mary’s body because central nervous system tissue doesn’t regrow when cut. As a result, Jack’s right eye/hemisphere wouldn’t communicate via neurons with either Jack’s body or Mary’s.
That doesn’t necessarily mean that Jack’s right eye/hemisphere would do nothing. What if it simply does what it is capable of doing — mediating Jack’s visual perception from his right eye?
Jack would see out of his left eye/hemisphere. But he might also see something out of the transplanted right eye in Mary’s skull, even if he and Mary are thousands of miles apart. He would have something like double vision — two superimposed scenes, a thousand miles separated.
But how is this possible, even in a thought experiment? How does the right eye/hemisphere communicate with Jack? By what medium?
We tend to assume that there must be a medium of communication both between our eyes and our whole brain in order to see. But people who have had split brain surgery see quite well even though their hemispheres have been separated (thus there is no direct connection). If the eyes (and hemispheres) are separated by 4000 miles, would the principle be any different? On this view, we see where our eyes are, not matter how far they are apart.
Michael Egnor, “What if only part — not all — of your brain were transplanted?” at Mind Matters News
Our senses don’t actually work quite the way we think.
Note: Posting here a comment under News in the combox, for clarification, in response to a commenter:
“AaronS1978 at 1, it’s a thought experiment. Briefly, hearts pump blood and kidneys process urine. Unless you are getting distress signals, you don’t even know about it – because they are not sensory organs. They’re there to do a job, not to inform you about it.
The question is, if sensory organs were transplanted, whose would the sensations – if any – be? Dr. Egnor’s point is that it isn’t self-evident that there must be a specific kind of connection for sensation – split brain surgery demonstrates that, in his view. So, he asks, what would really happen in an experiment (that we hope will never be done)?”
Dr. Frankenstein has agreed to stay on a few more minutes to take your calls.
See also: Can cryogenics (freezing at death) preserve memories or consciousness? The question cryogenics of the connectome raises is, can we freeze and then recover consciousness itself as opposed to simply saving imprints of a person’s memories? Dr. Frankenstein is now taking your calls.
You may also wish to read: Are human brain transplants even possible? What would be the outcome if one person received transplants from the brains of others? If it’s not possible, there may be a good reason why not. If tiny bits of the brains from all the people in my neighborhood were transplanted into my brain, would there be a neighborhood in my skull? (Michael Egnor)
and
Researchers: our conscious visual perception lies outside our visual cortex. They concluded that the end step of perceiving where objects are occurs in the frontal lobes, a finding they describe as “radical”