Authors: Fabio Richlan.
Publication: Frontiers in Human Neuroscience (Frontiers). Volume 8, Article 347 2014 | DOI: 10.3389/fnhum.2014.00347
Orthographic depth (OD) (i.e., the complexity, consistency, or transparency of grapheme-phoneme correspondences in written alphabetic language) plays an important role in the acquisition of reading skills. Correspondingly, developmental dyslexia is characterized by different behavioral manifestations across languages varying in OD. This review focuses on the question of whether these different behavioral manifestations are associated with different functional neuroanatomical manifestations. It provides a review and critique of cross-linguistic brain imaging studies of developmental dyslexia. In addition, it includes an analysis of state-of-the-art functional neuroanatomical models of developmental dyslexia together with orthography-speciﬁc predictions derived from these models. These predictions should be tested in future brain imaging studies of typical and atypical reading in order to reﬁne the current neurobiological understanding of developmental dyslexia, especially with respect to orthography-speciﬁc and universal aspects.
Richlan F (2014) Functional neuroanatomy of developmental dyslexia: the role of orthographic depth. Front. Hum. Neurosci. 8:347. doi: 10.3389/fnhum.2014.00347
Summary and Conclusion
To sum up, dyslexia-related differences between deep and shallow orthographies can be expected in a variety of left hemisphere brain regions, depending on task and stimulus demands and age of participants. The two models (Pugh et al., 2000; Richlan, 2012) differ in many respects as for how they predict the degree and extent of engagement in these regions. In addition, differences between deep and shallow orthographies are likely to be reflected in the dynamic interactions between brain regions.
Evidence from cross-linguistic brain imaging studies on developmental dyslexia is scarce. The different approaches of classical between-subjects designs, within-subjects designs (in the case of bilingual participants), and artificial orthography learning paradigms should be continued and expanded in the future. In addition, meta-analysis might provide a valuable tool to synthesize and compare a high number of original studies, which were conducted within a single language. A comparable strategy was already successfully applied in the investigation of child and adult studies of developmental dyslexia (Richlan et al., 2011).
The investigation of typical and atypical reading processes in different orthographies yields important implications for the neurobiological understanding of developmental dyslexia. The given variations in OD and the role of English as an “outlier” orthography (Share, 2008) should be considered as an opportunity to test the current neurocognitive models and to refine them. The present review article contributes to this endeavor by providing orthography-specific predictions derived from two distinct conceptions of the functional neuroanatomy of non-impaired and dyslexic reading. These predictions should be tested in future brain imaging studies of reading.