Imagine waking up one morning to discover that you could no longer see letters or numbers. Instead, anything made up of Arabic numerals or the characters of the Latin alphabet—a telephone number, your own name—looked like a blur or a jumble of squiggly lines.
Michael McCloskey, a professor in the Department of Cognitive Science, recently identified just such a reading impairment: alphanumeric visual awareness disorder, or AVAD.
McCloskey first encountered the disorder in 2011, when James Brandt, director of medical psychology at Johns Hopkins Medicine, introduced him to an engineering geologist (called Thomas here) who had lost the ability to see most Arabic numerals.
“I was reading the mail, and it was blurred,” says Thomas, recalling the onset of his condition. “At first, I thought I was having some kind of eye issue.”
He wasn’t. Thomas has no trouble seeing most letters clearly. But digits are a different story. “I can see 0 and 1,” he says. “But I can’t see 2 through 9.” In their place, Thomas perceives a spaghetti-like tangle of lines and curves. He can no longer remember what those Arabic numerals look like, nor can he describe them—a serious problem for a man who spends his days reading and writing technical reports filled with numbers. “I don’t know what a 6 or 7 is,” he says. “I can’t tell you what it looks like, and I can’t write it or recognize it.”
Thomas suffers from a degenerative neurological condition, and it isn’t unusual for people with certain kinds of brain damage to experience difficulty with numbers. But those people can usually see the shapes of the digits clearly; they simply can’t remember what they represent. This was different.
The distortion that Thomas experiences with Arabic numerals was something new. But there were more surprises to come. When McCloskey and two of his graduate students, David Rothlein and Teresa Schubert, hooked Thomas up to an EEG machine and showed him sequences of images containing Arabic numerals along with other visual stimuli, Thomas’ brain produced telltale electrical signals indicating that it was apprehending everything he saw; Thomas just didn’t know it.
“We first thought that the information about the shape of the digits was getting scrambled up in Thomas’ brain, and that was why he wasn’t able to see them,” McCloskey says. “But it looks like his brain is processing the shapes of those digits and identifying them. What’s getting disrupted is his awareness of what he’s seeing.”
Not long afterward, McCloskey and his students encountered a 12-year-old stroke victim (identified here as Audrey) with a similar problem. Where most people see letters and digits, Audrey sees only blurs; yet her brain does appear to be recognizing the words and numbers she looks at, even if it won’t let her see them.
“In both cases, there is a dissociation between our conscious experience of things and our ability to process things,” says Rothlein. “They’re definitely aware of something,” adds Schubert. “They’re just not aware of what the rest of us are aware of, and what they used to be aware of.”
McCloskey can’t say exactly which areas of Thomas’ and Audrey’s brains are affected, nor can he say why their shared condition has only now come to light, though he suspects it could easily be mistaken for more commonly diagnosed reading disabilities. Nonetheless, he has been able to help Thomas and Audrey cope with its impact.
For Thomas, the answer lay in devising a brand-new set of shapes for the numerals 2 through 9. For Audrey, it involved drawing a double line through otherwise standard characters, modifying them just enough so that she could see them again. Equipped with iPads and laptops tricked out with customized fonts and reading apps developed by former lab member Satyam Ghodasara, Thomas and Audrey can once again read what their brains had rendered incomprehensible, so long as it appears onscreen.
The specificity of the impairment—Audrey can still see symbols like “%” and “$,” while Thomas has no trouble with Roman numerals—raises tantalizing questions about how the brain organizes visual information, while the gap between experience and unconscious processing raises equally tantalizing ones about the nature of consciousness itself. McCloskey hopes that future research will answer those questions, while providing help for people like Thomas and Audrey. The research might also eventually lead to better treatments for other perceptual and language deficits resulting from brain damage.
“You need to have some understanding of what’s gone wrong,” McCloskey says, “in order to do something about it.”