Letter Reversals in Dyslexia: Is the Case Really Closed? A Critical Review and Conclusions

Abstract

Summary Reading is an automated desymbolization involving parallel operating subfunctions from which the major ones belong to the visual or the language comprehension domain, coordinated by guiding cognitive subfunctions. In this review, theories on dyslexia are subdivided according to what subfunction(s) is (are) primarily assumed to be impaired, to the level of processing on which the deficit is assumed to be affective, and to whether the theory is a mono- or multicausal one. The heterogeneity of theories and empirical results are explained by the inconsistency of methodological approaches, the differing definitions of dyslexia, and shortcomings in the interpretation of experimental results attained after functional fragmentation of the reading process. Empirical studies on reversal errors are critically reviewed and re-interpreted on the basis of the Functional Coordination Deficit Model. Within this multicausal model, reversals are assumed to be a symptom of a deficit in the coordination of visual and phonological decoding in a subgroup of reading disabled children. It is argued that in order to learn to read, it is important to treat graphemes as symbols instead of objects. Whereas symmetrically related objects are learned to be represented by similar patterns of neural activity in visual object recognition, such a symmetry-generalization in reading is a hindrance. A failure in suppression of visually symmetrical information in the representation of visual symbols produces ambiguous relations between visual and phonological information, disturbs the functional coordination, and may cause problems in learning to read. It is emphasized that reversals do not reflect a visual deficit or an incomplete hemispheric dominance, and that they are not the one and only symptom of dyslexia. Key words: reading, dyslexia, reversals, symmetry generalization, functional coordination deficit Theories on reading disability Systematic research on reading disability has a history of more than 100 years. However, there is still no consistency about the etiology of reading disability. In fact, theories on reading disability are very inconsistent and sometimes even contradicting. This may be due to the inconsistency in (1) the understanding of the reading process as such (cf., Rayner, 1993), (2) the point the phenomenon is viewed from, that is, symptomatically, etiologically, or from intervention/teaching (cf., Tonnessen, 1995) and (3) methodological approaches (cf., Lachmann, 2002). To bring light into this heterogeneous field, it may be useful to classify models of reading disability according to various aspects. Reading (including silent reading) may be thought of as comprising two major processes: (1) visual decoding of the message presented in a written form, including configurational (feature) and orthographic (word form) analyses; and (2) language comprehension of this message, including phonological, semantic and syntactic decoding (Friederici & Lachmann, 2002; Lachmann, 2002). However, reading cannot be defined as simply the sum, but rather as an interaction of these two major components. Firstly, the visual processes involved in reading are not identical to those in visual object recognition. Instead, the visual subfunction has to be considered as a highly specialized, fast and accurate desymbolization of visual icons (e.g., van Leeuwen & Lachmann, 2002). The same holds for the phonological processing which cannot simply be seen as a higher stage of auditory processing (Mann & Liberman, 1983). As for instance argued by Liberman (1998), speech consists not of acoustic sounds, but rather of distinctly phonetic gestures of the articulatory organs. Secondly, it seems unquestionable that the subfunctions involved in reading do not operate in serial. Even though it may be clear that reading starts in fact with a visual analysis of the configuration of the written form of a message. …

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