on September 14th, 2011 No Comments
Odds are you haven’t put too much thought into it, but a small region of your ventral occipitotemporal cortex is activating like mad as you read this sentence. First discovered a decade ago, the Visual Word Form Area, or VWFA, is an area of the visual cortex that appears to be devoted specifically to recognizing words.
It’s a skill you really shouldn’t take for granted. In a small segment of the population, the VWFA doesn’t work the way it should. Sufferers of pure alexia, or word blindness, can write, speak, and understand words – they just can’t read them. The condition is typically caused by a lesion that disrupts the visual system’s input to the VWFA, ensuring that the area never even has a chance to interpret visual information.
Unfortunately for alexia sufferers, repairing these sorts of connections is, for the moment, out of the question. And so, asked Andreas Rauschecker, an MD/PhD candidate in Stanford’s Medical Scientist Training Program, why not go around them?
Instead of being “luminance-defined,” [defined by contrasting shades] words can be “motion-defined” – distinguishable from their background not by color or contrast, but by their apparent direction of movement. Against a field of dots moving one way, words made up of dots moving in the other direction will “pop out” to most viewers, even if the word and background dots are the same shade.
…Participants in the study were asked to read while their brains were scanned by a functional MRI (fMRI) machine. The researchers presented the participants with various types of words – defined by either motion or luminance contrast – and watched for activation of the VWFA.
The researchers reasoned that, if the VWFA were only looking for a basic visual feature, such as the shapes of black-on-white letters, it shouldn’t activate in the presence of motion-defined words. But scans showed that the VWFA responded equally to all legible words.
Through a combination of fMRI scans and targeted disruption of brain activity, Rauschecker demonstrated that this was because the human MT complex, or hMT+ – a region of the visual cortex normally responsible for motion perception – was acting as an alternate pathway to the VWFA.
“How exactly the information ends up in the VWFA depends on the specific visual features,” Rauschecker told me. “There’s very flexible routing.”
For pure alexia sufferers who can’t distinguish typical, black-on-white words, the researchers suggest using electronic fonts that incorporate movement – effectively detouring visual information around the damaged area.
Photo by Artotem
Guest blogger Max McClure is an intern at the Stanford News Service. He recently graduated from Stanford with a degree in biology.