One of the first studies to look at phonological awareness in individuals with Down syndrome was Cossu, Rossini and Marshall (1993). They administered tasks of phoneme segmentation, phoneme blending and onset deletion to 10 children with Down syndrome aged 8-15 years and 10 typically developing children aged 6-7 years who were matched on reading accuracy. The children with Down syndrome performed significantly worse than the typically developing children on all the phonological awareness tasks. From these results, Cossu et al. argued that phonological awareness is not involved in reading for individuals with Down syndrome and thus phonological awareness is not a necessary prerequisite for learning to read. However many flaws with this study have been highlighted, including a large degree of
variability in the phonological awareness scores of the children with Down syndrome, which showed that some of the children had measurable levels of phonological awareness (Byrne, 1993). Furthermore Cardoso-Martins and Frith (2001) argued that some of the tasks used by Cossu et al. were very cognitively demanding. Indeed their phoneme blending task included items with six phonemes; as individuals with Down syndrome have low verbal memory spans, typically lower than six (Kay-Raining Bird & Chapman, 1994), it is perhaps unsurprising they would find this task difficult. Thus the children with Down syndrome may have found these tasks difficult for reasons other than having poor phonological awareness.
It seems that this early research into the phonological awareness skills of children with Down syndrome reached prematurely negative conclusions due to methodological flaws. More
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recent research has illustrated that individuals with Down syndrome can indeed demonstrate measurable levels of phonological awareness, and this will now be discussed.
Kennedy and Flynn (2003) investigated the levels of phonological awareness in a group of nine children with Down syndrome aged 5-8 years. Rime detection, alliteration detection, initial phoneme isolation and phoneme blending were assessed, using tasks which required a multiple-choice nonverbal response. There was a range of abilities within the group; some children did not score above chance on any task whilst some children scored above chance on multiple tasks. Although this study only included nine children, it showed that individuals with Down syndrome can perform above chance on phonological awareness tasks.
Many studies focussing on phonological awareness and reading accuracy have included typically developing control groups and larger sample sizes. Cardoso-Martins and Frith (2001) matched 33 individuals with Down syndrome and 33 typically developing children on reading accuracy and investigated their phonological skills. The typically developing group were aged 6- 9 years, whereas the individuals with Down syndrome ranged from 10-49 years. The typically developing children performed significantly better on an initial phoneme deletion task but both groups performed close to ceiling on an easier task of initial phoneme detection. It appears, therefore, that some elements of phonological awareness are less developed in individuals with Down syndrome in comparison to reading accuracy while others may be in line. However due to the large age range of the individuals with Down syndrome there is likely to be great variation in the type of schooling, and therefore reading instruction, experienced.
Other studies have also utilised reading accuracy matched control groups with different phonological tasks, and the results appear to converge on Cardoso-Martins and Frith’s (2001) findings. Snowling et al. (2002) found that individuals with Down syndrome performed significantly poorer on measures of syllable segmentation and phoneme detection than a reading accuracy matched typically developing control group. However, these
differences were no longer significant when receptive vocabulary, used as an index for general ability, was controlled for. In a second experiment, a phoneme detection task was
administered which targeted both initial and final phonemes. The two groups performed similarly on the initial phoneme detection task but there was a trend for the children with
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Down syndrome to score more poorly than the typically developing children on the final phoneme detection task. However in this second experiment, the group of children with Down syndrome were better readers than the typically developing children. In Roch and Jarrold’s study (2008) there was no difference on a phoneme detection task between individuals with Down syndrome and a reading accuracy matched group of typically developing children, although the typically developing group did perform significantly better on measures of phoneme deletion. Therefore it appears that individuals with Down syndrome do have difficulties with phonological awareness but this is not consistent across studies.
The inconsistency of findings may be due to the different phonological awareness measures used by different studies, as these tasks can vary in their degree of complexity. Individuals with Down syndrome appear to be relatively unimpaired compared to their reading accuracy skill on simple tasks such as phoneme matching (Fletcher & Buckley, 2002, Cardoso- Martins & Frith, 2001; Roch & Jarrold, 2008; Snowling et al., 2002). Performance on tasks requiring a greater degree of manipulation, such as blending and segmentation, is less clear- cut, with conflicting results (Boudreau, 2002; Cossu et al., 1993; Fletcher & Buckley, 2002). However, difficulties with the more complex task of phoneme deletion have been consistently found (Cardoso-Martins & Frith, 2001; Cossu et al., 1993; Roch & Jarrold, 2008). Therefore it appears that individuals with Down syndrome may have lower-level phonological skills commensurate with their reading accuracy, but tasks requiring a greater degree of manipulation prove more challenging.
Phonological awareness tasks can assess different units of sound: whole words, syllables, onsets and rimes or phonemes. Snowling et al. (2002) administered alliteration and rime tasks, designed to have the same format and to have relatively low cognitive demands. The group of children with Down syndrome only scored above chance in the alliteration task, whereas the reading accuracy matched typically developing control group scored above chance in both tasks. This particular deficit in rime has been replicated in other studies (e.g. Cardoso- Martins, Michalick, & Pollo 2002; Gombert, 2002) and raises the possibility that children with Down syndrome may be biased towards the initial sounds of words, especially as relative weaknesses have also been found on tasks focussing on final phonemes (Snowling et al., 2002).
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Children with Down syndrome typically have lower mental ages than reading accuracy matched typically developing control groups, which may result in more difficulty understanding task demands. This can be tested by comparing the phonological awareness skills of individuals with Down syndrome and typically developing children matched on nonverbal ability.
Boudreau (2002) administered a large test battery to 20 children with Down syndrome aged 5- 17 years and 20 typically developing children aged 3-5 years matched on nonverbal ability. It was found that individuals with Down syndrome performed at a similar level as nonverbal ability matched typically developing children on measures of blending and syllable
segmentation, but the typically developing group performed significantly better on tasks of rime judgement and alliteration judgement. This study suggests that the difficulties with phonological awareness typically seen in children with Down syndrome are not wholly due to their lower mental age.