Discovering and Treating a New Form of Reading Impairment
We have discovered a previously unknown perceptual deficit that selectively affects the ability to see letters and numbers. Two cases of the impairment (which we are calling Alphanumeric Visual Awareness Disorder, or AVAD) have been identified, and we are actively searching for additional cases, probing the causes and consequences of the disorder, and working to develop treatments.
MTS, a 12-year-old girl, has a large arteriovenous malformation in her brain.
In April 2011 the sixth-grade student suffered a stroke that left her with a restricted but devastating deficit in visual perception. MTS’s vision is normal, with one major exception: When she looks at a letter or digit, she sees only a blur, and as a consequence she is entirely unable to read words or numerals.
Remarkably, MTS perceives shapes other than letters and digits normally, including typographic symbols such as the number (#) and percent (%) signs. In addition she can identify letters or digits when she sees them drawn in the air.
RFS, the second individual identified with AVAD, is a 61-year-old man with a progressive neurological disease. In October 2010 he suddenly found himself unable to perceive Arabic digits, such as 4 or 8. Since that time, he sees digits only as uninterpretable jumbles of lines (which he calls ‘spaghetti’). Unlike MTS, RFS can perceive most letters normally.
For both MTS and RFS the disorder affects the ability to perceive not only the affected digits or letters themselves, but also other visual stimuli in the vicinity. For example, both individuals were completely unable to identify pictures enclosed within or overlaid by affected letters or digits.
We are using behavioral, ERP, and fMRI methods to explore the multitude of scientific questions surrounding AVAD. How can brain damage disrupt the ability not just to identify but even to see letters or digits while visual perception remains otherwise normal? What brain regions are implicated in the deficit? What does the disorder imply about the cognitive and neural processes that underlie our awareness of the visual world? Intriguing preliminary results suggest that even when MTS and RFS are aware only of a blur or jumble of lines, their brains are nevertheless processing the letters, digits, or nearby stimuli in the absence of awareness. See this poster for some of the results from RFS.
Another important set of questions concerns the range of variation within the disorder. The impairments experienced by MTS and RFS are very similar, yet not identical, suggesting that other variants of AVAD may remain to be discovered. Knowledge about the forms of AVAD should lead to better understanding of the causes and consequences of the disorder.
We are also working to develop adaptations for overcoming the effects of the disorder. Initial results have been extremely encouraging. We found that although MTS sees ordinary letters or digits only as blurs, she is able to see and identify letters and digits displayed in a modified font that adds two horizontal lines to each character, essentially a double strikethrough:
With this font installed on her laptop, MTS is now able to read for the first time in more than a year. She is once again able to read her school assignments (as well as email her friends and use Facebook).
For RFS the team devised a new set of digit characters.
He was able to see the new digits normally, and readily learned to use them. With the fonts on his computer modified to display the new digits, and a calculator app that also displays digits in this form, RFS now does all of his numerical work in the new digit format. These adaptations have enabled him to continue working at his number-intensive job.
A central question on our current agenda is, How prevalent is AVAD? Is the disorder very rare, or might it be more common, frequently going un- or mis-diagnosed? Progress in understanding AVAD should have both scientific and practical implications, advancing our knowledge of reading and visual awareness, and improving the lives of those with this disruptive disorder.