How do kids acquire new vocabulary? This process is poorly understood.
An influential theory has been that the phonological loop in working memory provides essential support. The phonological loop is like a little tape loop lasting perhaps two seconds; it allows you to keep active a sound you hear.
The idea is that a new unfamiliar word can be placed on the loop for practice and to keep it around while the surrounding context helps you figure out the meaning.
If so, you'd predict that the larger the capacity of the phonological loop and the greater the fidelity with which it "records" the better children will be able to learn new vocabulary.
The efficacy of the phonological loop is measured by having kids repeat nonsense words. Initially they are short--tozzy--but they increase in length to pose greater challenge to the phonological loop--liddynappish.
Several studies have shown correlations between phonological loop capacity and vocabulary size in children (for a review, see Melby-Lervag & Lervag, 2012).
The problem: it could be that having a big vocabulary makes the phonological loop test easier, because it makes it more likely that some of the nonsense words remind you of a word you already know. (And so you have the semantics of that word helping you remember the to-be-remembered word.) Indeed, even proponents of the hypothesis argue that's what happens when kids get older.
What you really need is a study that measures phonological loop capacity at time 1, and finds that it predicts vocabulary size at time 2. There is one such study (Gathercole et al, 1992) but it used a statistical analysis (cross-lagged correlation) that is now considered less than ideal.
A new study (Melby-Lervag et al, 2012) used probably the best methodology of any used to date. It was a longitudinal study that tested nonword repetition ability and vocabulary once each year between the ages of 3 and 7.
They used a different statistical technique--simplex models--to assess causal relationships. They found that both nonword repetition and vocabulary show growth, both show stability across children, and both are moderately correlated, but there was no evidence that one influenced the growth of the other over time.
The group then reanalyzed the Gathercole et al (1992) data and found the same pattern.
This is one depressing paper. Something we thought we knew--the phonological loop contributes to vocabulary learning--may well be wrong.
If anyone is working on a remediation program for young children that centers on improving the working of the phonological loop, it's probably time to rethink that idea.
Gathercole, S. E., Willis, C., Emslie, H., & Baddeley, A. (1992). Phonological memory and vocabulary development during the early school years: A longitudinal study. Developmental Psychology, 28, 887–898.
Melby-Lervåg, M., & Lervåg, A. (2012). Oral language skills mod-erate nonword repetition skills in children with dyslexia: A meta-analysis of the role of nonword repetition skills in dyslexia. Scientific Studies of Reading, 16, 1–34.
Melby-Lervåg, M., & Lervåg, A., Lyster, S-A H., Klem, M., Hagtvet, B., & Hulme, C. (in press). Nonword-repetition ability does not appear to be a causal influence on children's vocabulary development. Psychological Science.