Psychology

For many years, researchers have argued that the early phonological processing is responsible for early literacy skills. Rapid automatized naming (RAN) constitutes an additive source of variance to these skills. Recently a meta-analysis has investigated the above correlations in a set of 49 independent samples and has found significant correlations. However, no one knows which genes and environments influence the relation among phonological awareness, serial naming, and reading outcomes. In contrast, the specific loci for reading have been identified and replicated and are in the short arms of Chromosomes 2, 6, and 18.

For all the above reasons, the authors have decided to embark on the testing of 4 different hypotheses. A) genetics are primarily responsible for both the overlap as well as the independence between phonological awareness and rapid naming in predicting reading outcomes, B) genes contribute to a basic set of skills common to phonological awareness and rapid naming, but environmental influences control specificity C) in addition to shared genes, environmental influences control the relation between rapid naming and phonological awareness and last D) genes and environments are important to both overlap and independence.

The study employed participants from an ongoing Western Reserve Reading Project, employing 118 monozygotic (MZ) twin pairs (61 female) and 163 dizygotic (DZ) same-sex twin pairs (56 female), in kindergarten or first grade, living mostly in two parent households and white. Children completed a 90-min battery of cognitive and reading-related outcome measures in a home visit. The study measured two skills associated with reading (phonological awareness and RAN) and three variables (letter knowledge, word knowledge, and phonological decoding).

In the results, sibling similarity was greatest among MZ twins, followed by DZ twins suggesting that sibling similarity is accounted for by both additive genetic and shared environmental variance. Results further suggested a large overlap with specificity between phonological awareness and RAN in the prediction of reading outcomes i.e. naming speed variance and phonological awareness was found to correlate with reading outcomes through an additional shared environmental factor. Although the results suggest that a core genetic factor is accountable for the significant covariance between phonological awareness, rapid naming, and reading outcomes, there was no evidence for independent genetic effects on RAN.

Several shortfalls arise when we cast a closer look on the study sample employed to prove such an important genetic liaison, all of which have been also identified by the authors in the discussion section. First, the study population although heterogeneous in mix concerning the mothers education levels, has not been similar in either ethnicity (91 white), nor family composition. Of course, when studying for gene implications one would want to have as little heterogeneity as possible, but the restriction in the range of the results is a significant bias. Also, the children were not identical in age or school level, both important for the hypothesis tested. In general terms however, the paper is interesting and very well referenced to back up the slightest of doubt in the evidence produced.

In conclusion, the authors state the importance of naming speed on the variance of reading skills, a relation that might constitute a second separate factor in predicting reading outcomes( although this should not be adopted lightly).Further studies should prove if naming speed ability lies outside the phonological processing domain.