different span measurements other than the ones on which they were selected.
A second explanation would involve the acquisition by the three improved subjects of more sophisticated mnemonic strategies as an aid to performance on span tasks. Whereas it is clear that such strategies can improve performance on span tasks, it is not clear that they would be useful as a a memory support during reading ( Torgesen, Kistner, & Morgan, 1988). Thus, this explanation could not account for the comparable reading scores between the improved LD-S and the LD-N group. The last explanation, of course, is that these three (or at least two of them) subjects simply underwent marked improvement in their phonological coding skills over the past 9 years; that is, they may have been suffering a severe developmental lag in maturation of the brain systems that support phonological processing at age 10, but between ages 10 and 19, the particular brain system in question attained a more normal level of development.
In focusing on the three subjects who showed improvement in span performance over the past 9 years, we should not overlook the fact that approximately 60% of the LD-S children showed striking continuities in their span performance over a very long period of time. Further, these continued difficulties in coding the phonological features of verbal stimuli were associated with virtually no improvement in basic reading skills over the same period of time. Although these findings are admittedly preliminary, they suggest that the difficulties in phonological processing identified by poor performance on span tasks meet at least some of the requirements for explaining the intransigent nature of many reading difficulties. As such an explanation, they may not only account for difficulties in learning to read, but difficulties in attaining normal levels of awareness of the phonological features of language.
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