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Dehaene and colleagues proposed that skilled reading involves an adaptation of general object-identification processes in ventral occipitotemporal brain areas to the specific characteristics of printed words

according to the dominant theories of reading, orthographic processing is still primarily considered to be an extension of already established linguistic skills in the domain of spoken language processing

We challenged the hypothesis that learning an orthographic code depends on preexisting linguistic knowledge by investigating whether nonhuman primates can learn this skill.

the word versus nonword discrimination could be made implicitly on the basis of statistical dependencies between letters.

More detailed analyses revealed that baboons were not simply memorizing the word stimuli but had learned to discriminate words from nonwords on the basis of differences in the frequency of letter combinations in the two categories of stimuli (i.e., statistical learning).

words that were seen for the first time triggered significantly fewer “nonword” responses than did the nonword stimuli

Even more striking is the strong linear relation, shown in Fig. 4, between accuracy in response to nonword stimuli and their orthographic similarity to words that the baboons had already learned. The more similar a nonword was to a known word, the more false positive responses it produced.

Our findings have two important theoretical implications. First, they suggest that statistical learning is a powerful universal (i.e., cross-species) mechanism that might well be the basis for learning higher-order (linguistic) categories that facilitate the evolution of natural language (18, 19). Second, our results suggest that orthographic processing may, at least partly, be constrained by general principles of visual object processing shared by monkeys and humans.

Our study may therefore help explain the success of the human cultural choice of visually representing words using combinations of aligned, spatially compact, ordered sequences of symbols. The primate brain might therefore be better prepared than previously thought to process printed words, hence facilitating the initial steps toward mastering one of the most complex of human skills: reading.

Our results indicate that baboons were coding the word and nonword stimuli as a set of letter identities arranged in a particular order. Baboons had learned to discriminate different letters from each other (letter identity) and to associate those letter identities with positional information. Their coding of the statistical dependencies between position-coded letters is reflected in (i) their ability to discriminate novel words from nonwords (i.e., generalization), (ii) the significant correlation between bigram frequency and the accuracy of responses to words, and (iii) the increase in errors in response to nonword stimuli that were orthographically more similar to known words.