Thursday, April 02, 2009

More on rapid naming (RAN, phonemic awareness (PA) and reading: Genetic evidence

The importance of RAN (rapid automatic naming) and PA (phonemic awareness) for reading (and Dx of dyslexia) has been blogged and logged at this blog previously.

Toady I skimmed a nice bit of behavioral genetic research (Naples et al., 2009) in the journal Biological Psychology that reports on the unique and shared genetic variance of the constructs/traits of RAN and PA. Although a lengthy, and at times, complex article, the bottom line is that behavioral genetic evidence suggests that RAN (placed under Glr in CHC taxonomy) and PA (under Ga in CHC taxonomy) are different constructs, although they do have some shared genetic variance.

As articulated by the late John Horn, evidence for differences in constructs comes from multiple sources--structural (factor analytic), behavioral genetic, developmental, criterion-outcome, and neurocognitive. This study provides construct validity evidence in the form of behavioral genetic evidence.

This work’s objective was to offer additional insights into the psychological and genetic bases of reading ability and disability, and to evaluate the plausibility of a variety of psychological models of reading involving phonological awareness (PA) and rapid naming (RN), both hypothesized to be principal components in such models. In Study 1, 488 unselected families were assessed with measures of PA and RN to investigate familial aggregation and to obtain estimates of both the number and effect-magnitude of genetic loci involved in these traits’ transmission. The results of the analyses from Study 1 indicated the presence of genetic effects in the etiology of individual differences for PA and RN and pointed to both the shared and unique sources of this genetic variance,which appeared to be exerted by multiple (3–6 for PA and 3–5 for RN) genes. These results were used in Study 2 to parameterize a simulation of 3000 families with quantitatively distributed PA and RN, so that the robustness and generalizability of the Study 1 findings could be evaluated. The findings of both studies were interpreted according to established theories of reading and our own understanding of the etiology of complex developmental disorders.
Technorati Tags: , , , , , , , , , , , , , , , , , , ,

No comments: