A neurogenerative disorder cost a U.S. man the ability to perceive the digits 2 through 9, researchers say.

The man, whose case is described in a paper recently published in the journal Proceedings of the National Academy of Sciences, was 60 years old and working as an engineering geologist when he suffered an unknown “neurological event,” according to study co-author Teresa Schubert, who is affiliated with the department of psychology at Harvard University.

This caused severe headaches, temporary loss of vision and some speech difficulties, she said.

These symptoms eventually cleared up, but the patient, who the researchers identify by the initials “RFS”, noticed something else: he couldn’t see numbers.

“If you show him any number between two and nine, he can’t see it. He sees this scramble of black lines instead of seeing the eight or the four that’s in front of him,” Schubert said.

As an engineer, “math was a big part of his life,” she said, so no longer seeing numbers was very disruptive, eventually causing him to retire from his job.

That problem was mostly isolated to numbers too, she said. The researchers put him through a series of tests and found that he could still read and write, aside from occasional difficulty telling the difference between the letters M and N, or S and Z.

But numbers appeared “weird,” Schubert said. Not only that, but the “scramble” of lines wasn’t consistent — the digit “4” looked different every time, so he couldn’t re-learn the new image.

“I don’t know, folks, this is too strange for words,” RFS said in a video showing him trying to describe what he saw when he looked at a large foam number 8 he held in his hands. Feeling it, he said, it felt round, but the shape didn’t look round to him.

He struggled to describe what he was seeing when he looked at the number. “It doesn’t have a shape,” he said.

When he was asked to draw what he saw, looking at an orange number 8 on a screen, his drawing was a mess of thick black lines on an orange background.

RFS was eventually diagnosed with a rare brain disorder, corticobasal degeneration, Schubert said, and researchers think this is the source of his number problem. It’s similar to Alzheimer’s, in that it is a degenerative disease of the brain, she said, but unlike Alzheimer’s, it doesn’t usually target the memory. Instead, it usually causes motor abnormalities.

When researchers first encountered RFS in 2011, he was showing few motor symptoms, but since then, they have become severe, Schubert said.

She thinks that his disease is affecting not his ability to see a number, but his ability to process the information, she said.

“His brain is detecting that it is there. But then those signals are in some way, you know, the wires are crossed or something. Something has gone fuzzy to where he then isn’t able to become aware or to actually see that 8 or that 4 his brain has detected.”

It’s not that he’s lost all numeracy either, Schubert said.

“We know that he’s perfectly able to do maths in his head,” she said. “He hasn’t lost any understanding of what numbers mean. He knows that 78 is larger than 77.”

Over the nine years that they worked with RFS, the researchers were actually able to help him with his problem, she said. They came up with new symbols, representing numbers, for him to use instead. So, a vertical line with two horizontal lines coming off it might represent the number “4,” she said.

RFS is able to see and understand these new symbols, Schubert said, and even do math with them. The research team built him a new calculator app for his phone, and a font for his computer, so that he could still calculate figures and read a webpage, without running into confusing digits.

Although she has never heard of a case quite like RFS before, she thinks it can help advance our understanding of how we perceive things.

“This case is really telling us about the way all of our brains work to process things that we see and to turn things that we see and that our brain detects into what we’re aware of.”

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