Baboons hang out in the bush, not in bookstores. Yet these avid nonreaders can learn to tell written, real words from nonsense words, a new study finds.
That surprising achievement is not the same as reading, say psychologist Jonathan Grainger of the University of Aix-Marseille in France and his colleagues: Baboons tested in the new study didn’t attach meanings to words. Critically, though, these animals demonstrated that the roots of deciphering alphabetic script lie in brain functions that have nothing to do with language, Grainger’s team reports in the April 13 Science.
“We think our baboons learned to distinguish between specific combinations of letters that mostly appear in words versus combinations of letters that mostly appear in nonwords,” Grainger says.
If so, his investigation challenges the long-standing assumption that knowledge about spoken language informs the earliest stages of reading acquisition. According to that perspective, children get the literary ball rolling by matching written letters to corresponding speech sounds.
Instead, Grainger proposes, reading initially taps into brain regions that recognize different objects by sight and that evolved in all primates. The baboons in the study drew on this capacity to track pairs of letters that distinguish real from bogus words. That knowledge enabled the monkeys to learn dozens of four-letter English words and to tell whether new four-letter sequences qualified as words or not.
“For the first time, we have an animal model of a key component of literacy — the recognition of the visual word form,” comments cognitive neuroscientist Stanislas Dehaene of the INSERM-CEA Cognitive Neuroimaging Unit in Gif-sur-Yvette, France.
For the new investigation, Grainger’s team studied six baboons housed in a research facility with indoor and outdoor areas. Monkeys had free access to touch-screen computers, which they could reach through openings in a partition.
In a series of computer sessions, the baboons learned to recognize English words, such as done and vast, and to distinguish actual words from four-letter nonsense strings, such as dran and virt. Animals received food if they touched a cross on a computer screen after seeing a word, or if they touched an oval shape after seeing a nonword. New words were presented to baboons as the animals’ pool of learned words expanded.
Over a month and a half, individual baboons learned to recognize between 81 and 308 words, which they distinguished from more than 7,000 nonwords with about 75 percent accuracy.
Rather than simply memorizing what specific words looked like after many presentations, monkeys came to realize that certain letter combinations distinguished novel real words from fake ones, Grainger says. Baboons correctly identified novel nonwords as bogus more often than they incorrectly tagged actual words seen for the first time as nonwords. Absent knowledge of letter patterns that characterize genuine words, baboons would have mislabeled many more unfamiliar words as nonwords, Grainger holds.
The results set the stage for future studies examining whether brain areas activated while baboons identify words and nonwords correspond to the area of the human brain that’s stimulated during reading, Dehaene says.
Dehaene and his colleagues have reported that, in people, reading selectively activates a left-brain region that they call the visual word form area. Responses of this neural tissue to written material become stronger as children get older and are related to reading ability.
Reading and writing originated roughly 5,000 years ago, so the visual word form area could not have evolved for those purposes in such a short time, Dehaene says. Neural terrain built for object and face recognition gets recruited for the visual word form area as people learn to discern letters and letter arrangements in words, he says.
The new findings also fit with a proposal by evolutionary neurobiologist Mark Changizi of 2AI Labs in Boise, Idaho, that the shapes of written scripts derive from the contours of objects in natural scenes that primate brains’ visual systems home in on.
By grounding written letters in shapes inherently preferred by the brain, “writing systems could be more easily learned and were thus more likely to survive and spread through a culture,” write neurobiologist Michael Platt and graduate student Geoffrey Adams, both of Duke University in Durham, N.C., in a commentary published in the same issue of Science.
Just as some people labor to read even deftly assembled scripts, two baboons in the new study struggled to learn to tell words from nonwords. “Understanding what determines how well a baboon performs on our discrimination task might offer some insights into a possibly visual component of reading deficits in certain dyslexic children,” Grainger says.
Back Story | Reading on the brain
Written language, and thus the ability to read, evolved relatively recently. So scientists assume that the act of reading must co-opt brain areas that originally evolved for other functions, such as vision and speech. Still, imaging studies suggest that learning to read may tune a chunk of the brain called the visual word form area to recognize the written word. Scans (left, brain viewed from below) have shown that looking at words turns on a spot (red) in the left hemisphere. This patch of cells, in the fusiform gyrus, doesn’t respond as strongly to letters arranged nonsensically and ignores words spoken aloud. “It’s picking up on statistical patterns and playing a huge role in the information processing of visual words,” says neuroscientist Bruce McCandliss of Vanderbilt University. But critics tend to emphasize other activities that turn on this part of the cortex. Naming colors or deciphering Braille can also activate it — suggesting that reading is just one use of this multifunctional area. — Devin Powell
