Top down or bottom up target selection with toddlers?

A new paper on the consonant repertoires of toddlers confirms the close relationship between early speech and language development: Sotto, C. D., Redle, E., Bandaranayake, D., Neils-Strunjas, J., & Creaghead, N. A. (2014). Fricatives at 18 months as a measure for predicting vocabulary and grammar at 24 and 30 months. Journal of Communication Disorders, 49, 1-12. Specifically these authors examined the relationship between consonant repertoires at 18 months and performance on the MacArthur-Bates Communicative Development Inventories: Words & Sentences (MBCDI: WS) at 18, 24 and 30 months. Although inventory size was not significantly correlated with vocabulary size and use of grammatical markers at 24 and 30 months, the presence of fricatives in the inventory at 18 months was associated with higher mean scores on the 24 and 30 month language tests in comparison to language test performance for toddlers who did not produce fricatives at the earlier age. The discussion nicely covers the many intervening variables that might account for this relationship. (Clarification added in response to reader questions: the children in the study were normally developing).

I was pleasantly surprised to find that all the raw data is presented in the paper so that the consonant repertoires for each of the 37 toddlers at 18 months could be examined directly. This allowed me to check whether these repertoires conformed to the expectations of the implicational hierarchy as described by Dinnsen et al in an older paper (the hierarchy is derived from earlier work by Jacobson I believe): Dinnsen, D. A., Chin, S. B., Elbert, M., & Powell, T. W. (1990). Some constraints on functionally disordered phonologies: Phonetic inventories and phonotactics. Journal of Speech and Hearing Research, 33(1), 28-37. The hierarchy takes a structural approach assigning the child to different levels on the basis of the phonetic feature “contrasts” that are present in the phonetic repertoire as shown in the table below, keeping in mind that the child does not have to use the phones contrastively; there need be only representatives of the opposing feature classes present in the repertoire. The hierarchy is said to be implicational because if a child produces the feature attributed to one level of the hierarchy it is theoretically impossible for the feature contrasts at any lower level to not be present. Therefore the presence of voiced and voiceless phones (Level B) implies the presence of labial and coronal place as well as obstruent, glide and nasal manner features (Level A). I examined each of the repertoires in the Sotto et al paper and determined the highest level represented for each child and noted any violations of the expectation of the implicational hierarchy. The results are shown in the table below.

Implicational Hierarchy

I find it to be very interesting that one third of the toddlers in this study do not meet the assumptions of the implicational hierarchy. For example if we consider the children who produced a Level C phonetic repertoire, in other words, the 24 22/37 toddlers who produced fricatives and or affricates, we find that 6 of these did so despite lacking glides (4 children) or nasals (2 children) in the inventory. In Dinnsen et al, 40 preschoolers with speech sound disorders were described and the 1 child that failed to meet the implicational assumptions of the hierarchy was assumed to have a “deviant” phonology. However, (as I have suggested for Dodd’s so-called “deviant” categories as well), deviant behaviors have a funny way of showing up in very early language development.

What are the implications of these data and my re-analysis for speech and language therapy? To be honest I am not sure. One thing that I am quite sure of is that the findings do not support the “complexity” approach to target selection – the idea proposed in Dinnsen et al is that treating Level E phone contrasts will cause the lower level contrasts to appear is if by magic because of the internally specified implicational relationship between the contrasts as if they were all linked together like Christmas tree lights. I have shown that this approach does not in fact work (see Rvachew & Bernhard, 2010). This is not to say that one should take the opposite approach by structuring your treatment approach to introduce features in the opposite direction, working your way up the levels from A to B (and contrary to some myths in circulation I have never recommended this). I think that the important thing to keep in mind is that children at this stage of phonological development are developing their phonology and their lexicons so as to enhance lexical contrast  rather than phonological contrasts and therefore one needs to take a language based core vocabulary approach in any case.

The problem that I have is that I have never been comfortable with the idea of picking any words that are “functional” and teaching them even if the child hasn’t a hope of approximating the word (those poor children with speech problems named Clarence are fortunately few!). I prefer to take a systematic approach introducing new phones to maximize the probability of success and the implicational hierarchy shown above is maybe not a bad start if you have a child with no consonant repertoire at all (this does happen sometimes). Another possibility is Daniel Ling’s approach (teach all manner classes at once at one place of articulation and then move to the next place, leaving voice contrasts to the end). On the other hand, given the broad variety of strategies evidenced by the children in the Sotto et al study maybe the notion of taking any words that are important in the child’s environment is both ecologically and theoretically defensible. I will come back with some summaries of Dodd’s work on the core vocabulary approach another time but I think that this is a problem worthy of more rigorous and empirical study with larger samples!