Clues emerge on how brain reads, spells.

Clues emerge to how brain reads, spells

After suffering extensive stroke-induced damage to the central portion of her brain's left side, a 77-year-old woman had trouble identifying the latter half of words. Her problem, investigated by a pair of researchers in Baltimore, has yielded some intriguing clues to the way the brain ordinarily recognizes a string of letters as a word.

The woman, referred to as N.G., could easily read the left sides of written words, regardless of their lengths. Though her vision and muscle control remained unaffected by the stroke, this woman consistently misidentified the right halves of the same words, even though she could name all their letters. N.G. also misread the right halves of almost all words presented vertically, rather than left-to-right. The same pattern held for forward and backward spelling, whether written or spoken.

Other researchers have observed that patients with damage on the left side of their brain may have difficulty recognizing objects that appear on the right side of the visual field, and vice versa. Neurologists call this disorder "unilateral neglect." But N.G. is the first to show deficits focused on the same end of a word, no matter which side of the visual field that half of the word is presented in, note Alfonso Caramazza of John Hopkins University and Argye E. Hillis of Health-South Rehabilitation Corp., both in Baltimore. For example, when shown the word "common" spelled backwards as "nommoc," N.G. read out "com." However, she made errors on "mon," even though the latter part of the word had been presented to her left side, where normally spelled words were always recognized.

N.G.'s performance suggests reading and spelling rely on representations of words in the brain positioned according to the central point of a string of letters, the researchers assert in the July 19 NATURE. To further illustrate this notion, they observe that when they added letters to the right end of a word, N.G. had an easier time reading it. For instance, she was much better at recognizing "contrast" in the word "contrastiveness" than at simply reading "contrast."

N.G.'s impairment is "unexpected and potentially informative," writes psychologist Stuart Sutherland of the University of Sussex, England, in an accompanying comment. But its true meaning remains baffling, he concludes.

If words are mentally positioned by their center point, Sutherland asks, why are those same words more easily lifted from memory by their first letters? While this tendency may help explain why a person more easily recognizes the left side of a word, he says, it offers no aid in deciphering why a string of letters is easier to recognize as a word if extra letters are added on.