Viersen-Bree-2019

Across languages, studies have shown that dyslexia may be persistent, late-emerging, or resolving (Catts, Compton, Tomblin, & Bridges, 2012; Leach, Scarborough, & Rescorla, 2003; Torppa, Eklund, van Bergen, & Lyytinen, 2015). Students’ literacy performance may even continue to float around the clinical threshold throughout development in both late-emerging and resolving cases. Mechanisms behind resolving literacy difficulties remain unknown, however. One explanation is that underlying cognitive deficits associated with dyslexia (phonological awareness [PA], rapid automatized naming [RAN], and verbal short-term memory [VSTM]; Vellutino, Fletcher, Snowling, & Scanlon, 2004) partly resolve during development. An alternative explanation is that cognitive deficits remain present but are compensated during development by strategies or processes associated with cognitive strengths. In this study, we test and compare these explanations for resolving dyslexia.

 

Research on adults with compensated dyslexia, generally high-functioning university students with dyslexia, has focused more explicitly on the combination of cognitive strengths and weaknesses and possible areas of compensation to explain resolved literacy difficulties. These studies showed that, at later ages, resolvers have persistent deficits in phonological and/or orthographic processing (Cavalli, Duncan, Elbro, El hmadi, & Colé, 2017; Law, Wouters, & Ghesquière, 2015; Miller-Shaul, 2005; Parilla, Georgiou, & Corkett, 2007), RAN, verbal memory and speed of processing (Miller-Shaul, 2005; Parilla et al., 2007). Compensation of reading difficulties is linked to strengths in morphological knowledge (Cavalli et al., 2017; Law et al., 2015), vocabulary (Law et al., 2015; Miller-Shaul, 2005), and orthographic knowledge (Bekebrede, van der Leij, Plakas, Share, & Morfidi, 2010; Miller-Shaul, 2005). As a result, literacy skills of students with compensated dyslexia are characterized by continuously low (non)word reading and spelling (MillerShaul, 2005; Parilla et al., 2007), but often with levels above those of students with uncompensated dyslexia (Birch & Chase, 2004; Cavalli et al., 2017), and sometimes with word-reading levels within the normal range (Law et al., 2015). Reading comprehension is generally not or no longer impaired (Birch & Chase, 2004; Miller-Shaul, 2005; Parilla et al., 2007). These findings indicate that underlying deficits remain detectable at later ages despite higher literacy levels and that pronounced cognitive strengths, especially those related to language subskills, are present.

 

 This study is one of the first to indicate some support for the twice-exceptionality view on compensation, across risk and protective factors and both at the group and individual level. Unlike Torppa et al. (2015), we found no indications that a resolving developmental delay in underlying skills was fully responsible for improved literacy levels of the students with resolving dyslexia. In our sample of gifted students, poorer literacy outcomes were associated with more severe deficits to some extent, providing some support for the core-deficit view. However, most students with resolving dyslexia still had persistent PA deficits, and more than half of the students in this group still showed RAN impairments.