Vocabulary is important for some, but not all reading skills

Although there is evidence for a close link between the development of oral vocabulary and reading comprehension, less clear is whether oral vocabulary skills relate to the development of word-level reading skills. This study investigated vocabulary and literacy in 81 children of 8-10 years. In regression analyses, vocabulary accounted for unique variance in exception word reading and reading comprehension, but not text reading accuracy, decoding and regular word reading. Consistent with these data, children with poor reading comprehension exhibited oral vocabulary weaknesses and read fewer exception words correctly. These findings demonstrate that oral vocabulary is associated with some, but not all reading skills. Results are discussed in terms of current models of reading development. Vocabulary is important for 3 Vocabulary is important for some, but not all reading skills It is well accepted that learning to read is intimately connected to children‟s underlying oral language skills. Most research has focused on the vital role that phonological skills play in the development of reading, while the potential importance of other aspects of oral language skill has been downplayed. In this paper, we consider the role of oral vocabulary in reading development. Specifically, we sought to investigate whether individual differences in vocabulary development relate to some, but not all of the following component reading skills: reading comprehension, text reading accuracy, recognizing words and deciphering nonwords. Oral vocabulary and reading skills It seems difficult to dismiss the idea that vocabulary plays an important role in the development of reading comprehension – the ability to understand connected text. Logically, children will need to know the words that make up a written text to fully understand it. Further, it seems likely that the relationship between vocabulary and reading comprehension will be reciprocal across development, as reading provides an opportunity to learn new word meanings (e.g., Beck, Perfetti, & McKeown, 1982). Consistent with this, children with poor reading comprehension tend to show relatively low levels of vocabulary knowledge (Nation, Clarke, Marshall, & Durand, 2004) and they are poor at using textual support to infer the meanings of new words (Cain, Oakhill, & Lemmon, 2004). It is less clear, however, whether oral vocabulary skills play an important role in the development of word recognition and reading accuracy. The Lexical Restructuring Model proposed by Metsala, Walley and colleagues specifies a relationship between vocabulary and word reading development, albeit an indirect one (e.g., Walley, Metsala, & Garlock, 2003). According to this account, oral vocabulary growth leads to the development of increasingly Vocabulary is important for 4 well-specified phonological representations, and it is these more fine grained phonological representations that promote reading development. A more direct role for oral language skills is conferred by connectionist models of reading development. The triangle model (e.g., Harm & Seidenberg, 2004; Plaut, McClelland, Seidenberg, & Patterson, 1996; see Figure 1) and approaches built upon it (e.g., Bishop & Snowling, 2004) provide a theoretical framework for considering the contribution of language skills other than phonology to word reading development. Early versions of the model focused exclusively on connections between orthography and phonology (Seidenberg & McClelland, 1989). However, more recent incarnations have emphasized the contribution of semantic knowledge knowledge of word meanings to word recognition and its development. To understand why this is the case, it is necessary to describe the model in some detail. It comprises a phonological pathway consisting of connections between representations of phonological and orthographic information. The other (semantic) pathway consists of mappings between semantic, phonological and orthographic representations. Although in the triangle model both pathways and all types of representation are involved in the computation of all words, Plaut et al. and Harm and Seidenberg found, as the model learned to recognize a corpus of printed words, that the balance between the two pathways changed – a process they termed division of labor. Early in training, the models‟ resources were devoted to establishing direct connections between orthography and phonology (the phonological pathway), akin to the early stages of learning to read. However, later in training, the computational model came to depend increasingly on mappings from orthography to phonology via semantics (the semantic pathway). This was particularly the case for those words with inconsistent orthographic-phonological mappings, exception words such as break and foot. Vocabulary is important for 5 Why should this be the case? In the early phases of reading development, children must establish a system of mappings between letters and sounds and it is well-accepted that this alphabetic or decoding system is underpinned by phonological skills in the oral domain (e.g., Brady & Shankweiler, 1991; Byrne, 1998; Goswami & Bryant, 1990). To become an accurate and efficient reader of the English language, however, a child must acquire a flexible word recognition system that embodies knowledge of both the regularities and the irregularities of the English orthography. A child must be able to read words for which decoding skills are not sufficient, such as exception words, wherein the mappings between spelling and sound patterns are inconsistent. For example, the word break could potentially be pronounced to rhyme with steak or freak; and a direct spelling-sound translation of the word yacht, would lead to a mispronunciation. In the triangle model all types of representation are involved in the computation of all words regardless of their consistency. However, simulations have shown that with training the semantic pathway becomes more important i.e., shows a greater behavioral effect for the computation of words with inconsistent orthographic-phonological mappings (Harm & Seidenberg, 2004; Plaut et al., 1996). Thus, a clear prediction stemming from the triangle model is that individual differences in the semantic pathway should relate to individual differences in word reading proficiency, more strongly so for words with less consistent spelling-sound mappings. The nature of semantic representation is not well-specified in current versions of the triangle model although it is reasonable to suppose that a child‟s oral vocabulary knowledge is a suitable index of semantic knowledge. Consistent with this prediction from the triangle model, Keenan and Betjemann (in press) suggested that semantic knowledge could provide compensatory support for exception word reading because in this case phonologicalVocabulary is important for 6 orthographic representations are weak. Some preliminary evidence for a relationship between semantic knowledge (vocabulary) and exception words was provided by Bowey (2001). Nation and Snowling (2004) provided additional support for the prediction that oral vocabulary skills are related to exception word reading. They assessed the reading and language abilities of a group of typically-developing children in a longitudinal study. Nation and Snowling found that performance on an expressive vocabulary task at age 8 years accounted for variance in exception word reading at age 13 years, even after controlling for individual differences in decoding (nonword reading). Although these findings are consistent with the predictions of the triangle model, they are difficult to interpret for a number of reasons. First, vocabulary was assessed at 8 years, and exception word reading was assessed at 13 years. Because exception word reading was not assessed at 8 years, there was no control for earlier exception word reading. Therefore, it was not clear whether vocabulary contributed to later exception word reading because of an earlier association with exception word reading, or whether the variance it explained was independent of this autoregression effect. A finding that vocabulary can still account for variance in later exception word reading after controlling for earlier exception word reading would provide strong evidence for an independent role of vocabulary in word recognition skills. Second, although there was a relationship between semantic skills and exception word reading, the specificity of this relationship is impossible to assess as they failed to measure reading of words that have more consistent spelling-sound mappings. As the triangle model posits a particular role for semantics when reading exception words, it is important to test this behaviorally by assessing how vocabulary relates to the reading of both exception words and non-exception words using parallel regression analyses. Vocabulary is important for 7 Children with poor reading comprehension Another source of evidence supporting the view that vocabulary plays a role in reading development comes from studies of children with reading comprehension impairments. Poor comprehenders make up approximately 10% of 7-11 year olds (e.g., Nation, 2005) and are defined as children who have at least age-appropriate reading accuracy skills, but have specific difficulty with reading comprehension. In terms of oral language, poor comprehenders have strong phonological skills but show weaknesses in other areas of language such as listening comprehension and vocabulary (Catts, Adlof, & Weismer, 2006; Nation et al., 2004). In addition to their problems with reading comprehension and associated problems with vocabulary (Cain, Oakhill, & Bryant, 2004), there is evidence to suggest that poor comprehenders have subtle weaknesses in reading words that have inconsistent spellingsound patterns. For example, Nation and Snowling (1998) found that despite poor comprehenders being tightly matched to skilled