Eliciting dyslexic symptoms in proficient readers by simulating deficits in grapheme-to-phoneme conversion and visuo-magnocellular processing.

Among the cognitive causes of dyslexia, phonological and magnocellular deficits have attracted a substantial amount of research. Their role and their exact impact on reading ability are still a matter of debate, partly also because large samples of dyslexics are hard to recruit. Here, we report a new technique to simulate dyslexic symptoms in normal readers in two ways. Although difficulties in grapheme-to-phoneme conversion were elicited by manipulating the identifiability of written letters, visual-magnocellular processing deficits were generated by presenting letters moving dynamically on the screen. Both factors were embedded into a lexical word-pseudoword decision task with proficient German readers. Although both experimental variations systematically increased lexical decision times, they did not interact. Subjects successfully performed word-pseudoword distinctions at all levels of simulation, with consistently longer reaction times for pseudowords than for words. Interestingly, detecting a pseudoword was more difficult in the grapheme-to-phoneme conversion simulation as indicated by a significant interaction of word type and letter shape. These behavioural effects are consistent with those observed in 'real' dyslexics in the literature. The paradigm is thus a potential means of generating novel hypotheses about dyslexia, which can easily be tested with normal readers before screening and recruiting real dyslexics.