1.5.2.1. The simple view of reading.
The simple view of reading highlights the importance of reading accuracy and oral language to reading comprehension (Gough & Tunmer, 1986). To look at the contribution of decoding to reading comprehension Fowler et al. (1995) categorised 33 individuals with Down syndrome into four groups on the basis of their decoding skill. This classification predicted performance on tasks of reading accuracy and comprehension but most interestingly reading accuracy was significantly better than comprehension and this gap increased as decoding skill increased, i.e. as reading accuracy improves, comprehension falls further behind, which suggests some other limiting factor. Considering the simple view of reading, it is logical to suggest that this limiting factor may be language.
There have not been many correlational studies with children with Down syndrome that have included a measure of reading comprehension. However in Boudreau (2002), reading comprehension and various measures of spoken language were assessed concurrently. It was found that reading comprehension correlated with measures of receptive vocabulary,
receptive grammar, MLU and narrative skills. When age was controlled for, MLU was the only language measure which remained significantly related to reading comprehension. The typically developing control group were matched on nonverbal ability and had an average age
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of 4;05. Due to their young age, they performed very poorly on the reading comprehension task making it difficult to make any meaningful comparisons between the two groups.
It is informative to investigate whether reading accuracy and oral language are differentially related to reading comprehension in typical development and Down syndrome when children have equivalent levels of reading comprehension. Roch and Levorato (2009) used such a design to investigate the contribution of listening comprehension along with word and nonword reading and speed to reading comprehension. A group of individuals with Down syndrome aged 11-18 years were pairwise matched on reading comprehension to a group of typically developing children aged 6-7 years, although the children with Down syndrome had better reading accuracy skills. For the typically developing children, listening comprehension and word reading speed, used as this is a more sensitive measure than accuracy due to Italian’s regular orthography, explained unique variance in reading comprehension. However for individuals with Down syndrome, only listening comprehension accounted for significant variance in reading comprehension. This suggests that poor listening comprehension, in the presence of good reading accuracy, may limit reading comprehension in Down syndrome. Levorato, Roch and Beltrame (2009) found that the performance of individuals with Down syndrome on this measure of listening comprehension was predicted by receptive vocabulary and receptive syntax. This suggests that these lower-level oral-language skills may constrain reading comprehension indirectly through listening comprehension.
In Roch and Levorato (2009) the scores of the speeded word reading in the group of children with Down syndrome were close to ceiling and had little variance, which may have limited the potential for a relationship with reading comprehension. However Nash & Heath (2011) also found that language, in this study receptive vocabulary, was more highly correlated with reading comprehension in children with Down syndrome than a group of typically
developing children with the same level of reading comprehension. Furthermore vocabulary remained significantly correlated with reading comprehension after reading accuracy had been controlled for. This study also included a group of children at the same reading accuracy level as the children with Down syndrome, and there was also a strong correlation between reading comprehension and vocabulary in this group. Therefore it was argued that the greater
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Down syndrome in Roch and Levorato was the result of higher levels of reading accuracy relative to the typically developing group.
1.5.2.2. Relationship between inference making and reading comprehension.
When reading a text, it is often necessary to go beyond the information explicitly given in the text and make an inference. Very few studies have looked at inference making in
children with Down syndrome, but there is some evidence for difficulty in this domain. Groen et al. (2006) reported the performance of KS, a girl with Down syndrome who had exceptional reading skills, on two tasks of reading comprehension: the Neale Analysis of Reading (NARA II; Neale, 1989) and Wechsler Objective Reading Dimensions Test of Reading Comprehension (WORD; Wechsler, 1990). For both tasks children read passages and answer questions. However, on the WORD the questions tend to be literal, whereas on the NARA more inferences are required (Bowyer-Crane & Snowling, 2005). KS performed worse on the NARA compared to the WORD leading the authors to suggest that she had a particular weakness in generating inferences.
The comparison between questions which require inferences or literal information was explored in a larger group of good readers with Down syndrome by Nash and Heath (2011). Four stories were designed which were followed by an equal number of literal and inferential questions. Children with Down syndrome were compared to typically developing children at the same reading accuracy level, typically developing children at the same reading
comprehension level and poor comprehenders who were also matched for reading
comprehension. The children with Down syndrome performed equivalently to the two groups of children matched on reading comprehension on literal questions, but scored significantly below these two groups on inferential questions. Therefore there is a clear discrepancy
between literal and inferential questions in Down syndrome, which was also present to a lesser degree for the children with reading comprehension impairment. This supports Groen et al.’s (2006) case study and suggests that children with Down syndrome may have a specific problem with inference-making and it is possible that this contributes to their reading comprehension difficulties.
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1.5.2.3. Relationship between working memory and reading comprehension. Verbal working memory is necessary for successful reading comprehension and children with Down syndrome have well documented difficulties with working memory. Therefore it is possible that this could limit their reading comprehension skills. The
contribution of working memory to reading comprehension in children with Down syndrome and how this compares to typically developing children was explored by Levorato, Roch and Florit (2011). The two groups of children were matched on reading comprehension, and also performed similarly on a working memory task. Working memory contributed unique variance to reading comprehension, after sentence comprehension and a short-term memory task were controlled for. Furthermore the relationship between working memory and reading
comprehension was similar in the two groups. In comparison, Nash and Heath (2011) found a stronger relationship between reading comprehension and working memory in children with Down syndrome than a group of typically developing children at the same level of reading comprehension; although this relationship was similar once reading accuracy was controlled for.
1.5.2.4. Longitudinal studies of reading comprehension.
The longitudinal studies with children with Down syndrome tend to either not include reading comprehension or not treat it as an outcome measure. The few studies that have, have noted poor progress, at a slower rate than for reading accuracy (Byrne et al., 2002; Laws & Gunn, 2002).
The only longitudinal study to specifically look at reading comprehension development in children with Down syndrome was carried out by Roch, Florit and Levorato (2011). Ten individuals with Down syndrome aged 11-19 years participated, and their reading
comprehension, listening comprehension and reading accuracy skills were assessed at two time points, 12 months apart. A regression analysis was conducted to investigate which initial skills predicted later reading comprehension. After the autoregressor of reading
comprehension had been entered, reading speed contributed 8% of variance, which was not significant, and listening comprehension contributed 32% of variance, a significant proportion. This confirms the pattern seen in the concurrent study by the same authors (Roch & Levorato,
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2009) of listening comprehension playing a larger role in reading comprehension for children with Down syndrome than reading speed. However due to the three-step regression analysis on data from only 10 participants, these results need replicating with a larger sample size.
1.5.2.5. Summary: Predictors of reading comprehension in Down syndrome. Children with Down syndrome have difficulties with reading comprehension in comparison to their reading accuracy skills. Considering the simple view of reading as a framework and weaknesses in the verbal domain, it is likely that oral language may limit reading comprehension. Indeed for children with Down syndrome who do reach good levels of reading accuracy, this appears to be the case. Higher-level processes, including working memory and inference-making, are also related to reading comprehension in Down syndrome. Again both these domains appear to cause difficulty for children with Down syndrome, which may then limit reading comprehension.
There has thus far only been one longitudinal study to specifically look at the
predictors of reading comprehension in children with Down syndrome. The results confirmed the greater contribution of oral language compared to reading accuracy seen in concurrent studies. However there is a pressing need for longitudinal studies with typically developing control groups, larger sample sizes and a larger test battery of possible predictors to confirm and extend these findings.