elementary school years. Being able to understand written texts does not only enable students to gain knowledge in almost all school domains, it is also a prerequisite to be able to participate in our modern literate society (Spörer & Brunstein, 2009). Comprehending written text is a complex process, involving various bottom-up and top-down processes. These processes are influenced by the quantity and quality of the lexical representations stored in the mental lexicon. The general aim of the present dissertation was to gain more insight in the role of lexical quality in reading comprehension and the development of such in the intermediate elementary grades (Grade 4 and 5). In the first part of this dissertation (Chapters 2 and 3), the relation between lexical quality and reading comprehension was examined. Two studies were conducted, one using an experimental design and one using a more naturalistic correlational design. In the second part (Chapter 4), we adopted a developmental perspective to examine causal relationships. In a longitudinal study, we examined the relation between lexical quality (i.e., decoding and vocabulary) and reading comprehension and how cognitive precursors influence this relation in students in the intermediate elementary grades. These grades mark a critical transition point in development, as students go from learning to read to reading for learning. In the third and final part (Chapter 5), we focused on changing reading behaviors and improving lexical quality and reading comprehension skills. In an intervention study, it was examined to what extent lexical quality and reading comprehension benefit from a reading comprehension intervention aimed at enhancing word-to-text integration skills. This final chapter gives a summary of the main findings and provides answers to the three research questions addressed in the introduction of the present dissertation. In addition, theoretical implications, limitations, and suggestions for future research and educational implications will be discussed.
6.1 LEXICAL QUALITY EFFECTS IN READING COMPREHENSION
In the first part of the present dissertation, we have demonstrated that there is a strong relation between lexical quality (i.e., decoding and vocabulary) and reading comprehension, which is in line with other studies examining this relation (e.g., Ouellette & Beers, 2010). As set out throughout this dissertation, lexical quality is dependent on the number of representations stored in the mental lexicon and the quality of these stored representations. Throughout the present dissertation lexical quality was measured using decoding and vocabulary tasks. Decoding tasks were used to assess the grapheme and phoneme constituents and their interconnections; Various vocabulary measures were used to assess the complexity of the mental lexicon and to account for the phoneme and semantic constituents and their interconnections (oral vocabulary) and the grapheme, phoneme, and semantic constituents
comprehension generally have accounted for individual differences in decoding, the complex structure of the mental lexicon has been largely ignored, underexposing the relation between lexical quality and reading comprehension. In the first part of the present dissertation we have shown that both decoding skills and various aspects of the lexicon uniquely contribute to explaining individual differences in reading comprehension skill. Moreover, we have shown that lexical semantic network knowledge (as one aspect of the mental lexicon) is also indirectly related to reading comprehension via its impact on word identification skills, one of the core skills in reading comprehension.
In Chapter 2, fourth-grade students completed an experimental visual primed lexical decision task. Results of this experimental study indicated that students were faster in identifying a word when it was preceded by a related word as compared to when it was preceded by an unrelated word. These results are in line with other studies examining lexical semantic network knowledge in students (e.g., Assink, Van Bergen, Van Teeseling, & Knuijt, 2004; Holcomb & Neville, 1990). This priming effect was found for categorically, functionally, and part-whole related words indicating that the nature of these priming effects is universal across tasks. In addition, it was shown that priming effects were not related to reading abilities (both decoding and reading comprehension), suggesting that children varying in reading ability all benefit from residual co-activation of related words in reading and understanding written text. Together the results indicate that priming effects are robust and universal across tasks and children varying in reading ability.
In Chapter 3, we adopted a multicomponent approach in order to account for the complex structure of the mental lexicon. Together a variety of operators to measure vocabulary explained up to 30% of the variance in reading comprehension. This amount is substantially larger as compared to other studies examining this relation using only one vocabulary measure. Ouellette (2006), for example, indicated that in Grade 4 only 15% of the variance in reading comprehension could be explained by individual differences in vocabulary. In addition to more conventional breadth and depth measures, students in our study also completed an offline word association task to measure lexical semantic network knowledge. Performance on this task uniquely explained individual differences in reading comprehension, after accounting for individual differences in decoding and other aspects of the mental lexicon. This result indicates that students with stronger and more meaningful connections between words, were more likely to have better developed reading comprehension skills as compared to students with weaker and less meaningful connections between words.
Based on the studies presented in the first part of this dissertation, it can be concluded that lexical quality is a complex construct, involving various aspects and that research should consider this complex nature. In Chapter 3 we have evidenced that various vocabulary measures