The man who can't see numbers

30 June 2020

Interview with 

Teresa Schubert, Harvard University

what_RFS_sees

Patient RFS can't see the numbers two through nine - instead, he just sees this scramble of lines.

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In Oliver Sacks' 1985 book 'The Man Who Mistook His Wife for a Hat', he documented some of the most unusual cases he’d encountered over his career as a neurologist, including - famously - his patient who couldn’t see faces. Sacks died 5 years ago, but he would have been absolutely fascinated by a report published this week on a man known only as RFS. Owing to a degenerative brain condition, RFS can’t consciously see any of the numbers between 2 and 9! Katie Haylor spoke to Teresa Schubert, who’s been studying the RFS' symptoms and what they can tell us about how consciousness works...

Teresa - RFS has difficulty seeing numbers. So if he looks at the number two or the number eight, instead of seeing that normally the way you or I would, he sees what he describes as "this tangle of black spaghetti". He also can't see anything that's in the same location. If you take a really big eight and you put a face in the centre of it, for you or I, we could see the eight and the small face in the centre; for RFS, that whole thing becomes this mess of scrambled stuff, he can't see that face. We were able to record his brain activity, and we found that his brain is actually detecting that face, even though he can't see it. So that suggests that not everything your brain is detecting actually becomes what you see. You are not necessarily aware of everything that your eyes take in and that your brain is processing. It's a very unique case. I had never heard of anything like this. And if you scour the published scientific literature, there's nothing quite like this that's been reported. And it tells us something really interesting. I think about the way what we see is being constructed by our brain. You don't just open your eyes and then see everything like it's a video recording. There's a lot of work that your brain is doing to process things and to show things to you.

Katie - Just to make sure I've got this right: this gentlemen can see letters normally, but he can't see the numbers two to nine. In fact, he can see zeroes and ones, but not the numbers two to nine. Is that right?

Teresa - That's right. Which is a really, I think, striking and surprising finding; it's very specific. And we do know that your brain has specialised areas for processing categories of things that we have a lot of experience with. There's a specialised brain area for processing faces, for processing letters, and for processing numbers. So it's not out of the realm of possibility that one of those areas could be disrupted in this way.

Katie - Why is the brain discriminating between different numbers?

Teresa - There are a couple of possible reasons for that. Zero and one are very simple shapes, so it may be that because those shapes have another interpretation, they're not necessarily being treated as a digit by his brain and being subject to this disruption. But zero and one also have special status, giving you information about place value: whether something's in the hundreds place or the ones place. And they also have a different role in number words, so the difference between 3 and 13 and 30 is about whether there's a one or a zero and what side it's on. Those are possible reasons why zero and one might be okay, even though the rest of the digits are so disrupted.

Katie - Do you think it's got anything to do with the nature of the image? Say if these numbers were in Roman numerals, or say you had four images rather than the number or the concept four; would that help?

Teresa - Yeah, so his ability to process numbers more generally is completely fine. He was an engineering geologist, so he was the guy who's responsible for making sure that your bridge is going to be strong enough to span the river, or your tower is going to still be standing in 20 years. And this deficit is really specific to the shapes of those digits, so Roman numerals are fine. If you write a number out in words, it's also fine.

Katie - In my head something's just hiding behind a wall or there's some sort of blockade. Do you know what it looks like what's happening?

Teresa - Our best guess is that the numbers are getting detected. And we know that because if they weren't getting detected as numbers at some level, then there would be no reason for only numbers to look weird to him. Everything would look weird. So we know numbers are getting detected as a digit. And then something goes wrong past that in the way that information gets passed on to what he actually becomes aware of, and what he sees in the world. And we don't know specifics about what that thing is that's going wrong. So this is a really clear case of seeing that something has gone wrong, but it's going to require a lot of additional study to see exactly how that next process works.

Katie - How does this study add to what we understand about conscious awareness?

Teresa - I think our study makes a small but important contribution into showing that we have many different steps and layers of processing that allow awareness to be generated. It really complicates the picture of what it means to be conscious and to be aware of something.

Katie - It is only one person's experience though. What can one person's experience tell us of how the brain works in general? There's a long history of using these individual case studies, as we call them, to learn about the way brains work in general. So we assume that before RFS developed this condition he had a normal brain, and what's happened is one part that's constructing this little corner of awareness for him has now been damaged and disrupted. And so by looking at what's gone wrong there, we can kind of work backwards and see like, "okay, here's what's not happening correctly for RFS. That means there's a part of the brain that's doing that for everyone."

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