MENTAL ROTATON OF LETTERS IN DYSLEXICS AND IMPLICATIONS FOR DIAGNOSIS AND EDUCATIONAL TREATMENT Patrycja Rusiak 1, 2 , Thomas Lachmann 2, 3 & Piotr Jaskowski 1,4 1 University of Casimirus the Great, Bydgoszcz, Poland, 2 University of Leipzig, Germany, 3 Brain Science Institute, RIKEN, Wako-shi, Japan, 4 Medical University of Lübeck, Germany r.pat@interia.pl Abstract A classical mental rotation task (Cooper & Shepard, 1975) was performed with dyslexics and non-dyslexics. Group differences were found for mean reaction time but there was no difference in mental rotation effects between the groups. The results were interpreted within the framework of the Functional Coordination Deficit model (Lachmann, 2002). It was concluded that dyslexics rotate the letters mentally just as good as non-dyslexics but have a problem to finally decide, whether the letter is normal or mirrored. This problem occurred because of a failure in suppression of symmetry in the representation of graphemes. Dyslexics represent letter like objects. Therefore, they fail to discriminate between orientational alternatives and for the same reason fail to establish unambiguous relation between grapheme and phoneme representations. According to the International Classification of Diseases, developmental dyslexia is a specific disability in learning to read and to spell adequately despite of at least normal intelligence, adequate instruction and socio-cultural opportunities. Furthermore, sensory defects in vision and hearing should be excluded as to be responsible for the problems in reading and writing. One of the major symptoms of dyslexia are reversal errors, that is, the children confuse letters which are horizontally or vertically symmetrical to each other or rotated (e.g., p / q; b / d; p / d). These errors are normal in beginning readers but become very rare after practice. In dyslexics, however, they still occur even after years of reading experience. Orton (1925, 1928) postulated that these problems reflect the cardinal symptom of developmental dyslexia. He assumed that these confusion errors (strephosymbolia) are caused by a faulty development of cerebral dominance and interhemispheric communication. Later on, phonological skills were considered as to be more relevant to explain dyslexia (e.g., Bradley & Bryant, 1978; Liberman et al., 1971). In this context, it was often argued that Orton believed that dyslexics have a perceptual deficit and actually see letters in a wrong orientation (Vellutino, 1977). However, as argued by others (Corballis & Beale, 1993; Lachmann, 2002; Lachmann & Geyer, 2003), Orton assumed reversals to be the result of labeling problems in memory and not of problems in visual perception. There are a couple of alternative models which try to connect the original ideas of Orton with more recent neurological theories (Corballis & Beale, 1993) and experimental results (Lachmann & Geyer, 2003; Brendler & Lachmann, 2001). One is the multicausal Functional Coordination Deficit