In my ongoing lay interest in questions of sentience, intelligence, and consciousness, I found interesting the following remarks from a conversation between Steven Strogatz and Anil Seth for The Joy of Why podcast.
Strogatz: That last comment makes me think about one of the most fascinating things — I mean, I really do love your book, I have to say — and one of the parts I had not known a thing about before had to do with human patients, who we used to describe as being in a vegetative state. What I was going for was a study where you talked about the use of having people imagine playing tennis, or moving around in their house, and what that has revealed about the conscious experiences of people that we might otherwise tend to deny having consciousness.
Seth: Right. So I think this example underlines that studying consciousness is not just some sort of luxurious indulgent pursuit to satisfy our existential itches. It’s something that has real practical importance. And in neurology, there are people who suffer very severe brain damage: They appear to be unconscious. You know, they don’t respond to any verbal commands or interactions. They don’t seem to display any voluntary behavior. But they still go through sleep and wake cycles. They’ll wake up, their eyes will open. But very informally, it seems like there’s nobody home.
My friend and colleague Adrian Owen, and his colleagues Melanie Boly and others a while ago, now more than 10 years ago, they did this now very famous experiment where they had a patient who was apparently in this vegetative state. And they asked her to do two things at different times. One time, they asked her to imagine playing tennis for about 30 seconds while in the brain scanner, by the way, and at other times, they asked her to imagine walking around the rooms in her house. Of course, there’s no obvious response.
But when you analyze what was going on in her brain, the areas of the brain that we know from other studies are heavily involved in planning smooth movements of the sort that you do when you’re playing tennis, those were highly active. And importantly, it’s not just the auditory cortex, it’s not just an automatic response to sound or language. These are the parts of the brain that light up when somebody understands the content and is actively engaging in imagination — stuff that’s very hard to conceive how it could be done without consciousness. And then when imagining walking around their house, same thing. There’s another set of brain regions, which are quite separate, which are again not just auditory or language areas, which reliably light up when people are imagining moving around in some sort of spatially organized way. And when she was given that instruction, we saw those areas light up.
The reason why this struck me, beyond its inherent interestingness, is because of something else I’d read somewhere that took me a while to track down because I couldn’t figure out the search terms to see if I’d blogged it, read an article about it, or saw it in a book.
As it turns out, I’d read two articles.
We were on the brink of a remarkable discovery. Following on from the findings with Helen, Weiskrantz took a new approach with a human patient, known by the initials DB, who, after surgery to remove a growth affecting the visual cortex on the left side of his brain, was blind across the right-half field of vision. In the blind area, DB himself maintained that he had no visual awareness. Nonetheless, Weiskrantz asked him to guess the location and shape of an object that lay in this area. To everyone’s surprise, he consistently guessed correctly. To DB himself, his success in guessing seemed quite unreasonable. So far as he was concerned, hewasn’t the source of his perceptual judgments, his sight had nothing to do with him. Weiskrantz named this capacity ‘blindsight’: visual perception in the absence of any felt visual sensations.
Blindsight is now a well-established clinical phenomenon. When first discovered, it seemed theoretically shocking. No one had expected there could possibly be any such dissociation between perception and sensation. Yet, as I ruminated on the implications of it for understanding consciousness, I found myself doing a double-take. Perhaps the real puzzle is not so much the absence of sensation in blindsight as its presence in normal sight? If blindsight is seeing and nothingness, normal sight is seeing and somethingness. And surely it’s this something that stands in need of explanation.
Then I’d encountered it again in a review of Humphrey’s book by Nick Romeo for The New Yorker.
As Humphrey tried to understand Helen’s condition, he recalled an influential distinction, made by the eighteenth-century Scottish philosopher Thomas Reid, between perception and sensation. Perception, Reid wrote, registers information about objects in the external world; sensation is the subjective feeling that accompanies perceptions. Because we encounter sensations and perceptions simultaneously, we conflate them. But there’s a difference between perceiving the shape and position of a rose or an ice cube and experiencing redness or coldness. Humphrey suspected that Helen was making use of visual perceptions without having any conscious visual sensations—using her eyes to gather facts about the world without having the experience of seeing. His doctoral supervisor, Larry Weiskrantz, soon made a complementary discovery: he observed a human patient, a partially blind man who was missing half his visual cortex, making consistently accurate guesses about the shape, position, and color of objects in the blind region of his visual field. Weiskrantz named this ability “blindsight.”
I guess what I am wondering, in my thoroughly and entirely lay fashion, is that if there is sightless seeing, effectively seeing without someone in there doing the seeing, is it at all possible that the patient in a vegetative state described by Seth might have been exhibiting a similar thing.
Do we know if “the parts of the brain that light up when somebody understands the content and is actively engaging in imagination” implicated in that situation could be active “merely” in the same way that there can be “visual perception in the absence of any felt visual sensations” in the situation of blindsight?