Savill-Thierry-2011
Authors: Nicola J. Savill, Guillaume Thierry.
Publication: Brain Research Volume 1385, Pages 192-205 2011 | DOI: 10.1016/j.brainres.2011.02.012
Deteriorated phonological representations are widely assumed to be the underlying cause of reading difficulties in developmental dyslexia; however, existing evidence also implicates degraded orthographic processing. Here, we used event-related potentials whilst dyslexic and control adults performed a pseudoword-word priming task requiring deep phonological analysis to examine phonological and orthographic priming, respectively. Pseudowords were manipulated to be homophonic or non-homophonic to a target word and more or less orthographically similar. Since previous ERP research with normal readers has established phonologically driven differences as early as 250 ms from word presentation, degraded phonological representations were expected to reveal reduced phonological priming in dyslexic readers from 250 ms after target word onset. However, phonological priming main effects in both the N2 and P3 ranges were indistinguishable in amplitude between groups. Critically, we found group differences in the N1 range, such that orthographic modulations observed in controls were absent in the dyslexic group. Furthermore, early group differences in phonological priming transpired as interactions with orthographic priming (in P2, N2 and P3 ranges). A group difference in phonological priming did not emerge until the P600 range, in which the dyslexic group showed significantly attenuated priming. As the P600 is classically associated with online monitoring and reanalysis, this pattern of results suggest that during deliberate phonological processing, the phonological deficit in reading may relate more to inefficient monitoring rather than deficient detection. Meanwhile, early differences in perceptual processing of phonological information may be driven by the strength of engagement with orthographic information.
Research highlights
► Orthographic and phonological priming compared in dyslexic adults (DYS) using ERPs. ► Absence of N1 orthographic priming in the DYS group relative to controls. ► Interactions in P2–P3 range driven by reduced orthographic effects in the DYS group. ► Main group differences in phonological reprocessing in the P600 range.
Savill, N. J., & Thierry, G. (2011). Reading for sound with dyslexia: evidence for early orthographic and late phonological integration deficits. Brain research, 1385, 192–205. https://doi.org/10.1016/j.brainres.2011.02.012
Conclusions:
This study provides electrophysiological evidence for early sensitivity to subtle phonological manipulations of visual pseudoword stimuli, but reduced sensitivity to whole from orthographic information during phonological analysis in dyslexic readers. A failure in stimulus integration and reprocessing, indexed by a significantly less discriminative P600, may account for the weaker performance of dyslexic participant in homophonic judgement. The phonological deficit, in pseudoword reading at least, might thus be better conceived in line with Ramus and Szenkovits’ (2008) conclusion regarding the recruitment of controlled, metacognitive processes in phonological analysis. Further research should determine the specificity of reduced orthographic effects in dyslexia and clarify the role of phonology in deliberate and implicit word recognition. Tasks which selectively manipulate the focus on phonological and orthographic information and the degree of attentional demand required should help to clarify the relative perceptual and executive aspects of reading deficits in dyslexia.
