Conversations with SLPs: Nonword Practice Stimuli

I often answer queries from speech-language pathologists about their patients or more abstract matters of theory or clinical practice and sometimes the conversations are general enough to turn into blog topics. On this occasion I was asked my opinion about a specific paper with the question being generally about the credibility of the results and applicability of the findings to clinical practice:

Gierut, J., Morrisette, M. L., & Ziemer, S. M. (2010). Nonwords and generalization in children with phonological disorders. American Journal of Speech-Language Pathology, 19, 167-177.

In this paper the authors conduct a retrospective review of post treatment results obtained from 60 children with a moderate-to-severe phonological delay who had been treated in the context of research projects gathered under the umbrella of the “learnability project”. Half of these children had been taught nonwords and the remainder real words, representing phonemes for which the children demonstrated no productive phonological knowledge. The words (both the nonword targets and the real word targets) were taught in association with pictured referents, first in imitation and then in spontaneous production tasks. Generalization to real word targets was probed post-treatment. Note that the phonemes probed included those that were treated and any others that the child did not produce accurately at baseline. The results show an advantage to treated over untreated phonemes that is maintained over a 55 day follow-up interval. Greater generalization was observed for children who received treatment for nonwords compared to those children who received treatment for real words, but only for treated phonemes and only immediately post treatment because over time the children who received treatment for real words caught up to the other group.

OK, so what do I think about this paper. Overall, I think that it provides evidence that it is not harmful to use nonwords in treatment which is a really nice result for researchers. As Gierut et al explain, nonwords are handy because “they have been incorporated into research as a way of ensuring experimental control within and across children and studies.” They can be designed to target the specific phonological strengths and needs of each child and it is very unlikely that the family or school personnel will practice them outside of clinic and therefore it is possible to conclude that change is due to the experimental manipulation. Gierut et al go one step further however and conclude that nonword stimuli might offer an advantage for generalization learning because “the newness of the treated items might reduce interference from known words.” Here I think that the evidence is weaker simply because this is a nonexperimental study. The retrospective nature of the study and the fact that children were not assigned with blind random assignment in one cohort to be taught with one set of stimuli vs the other while holding other aspects of the design constant limits the conclusions that one can draw. For example, the authors point out that the children who were treated with nonwords received more treatment sessions than those treated with real words. Therefore, in terms of clinical implications, the study does not offer much guidance to the SLP beyond suggesting that there may be no harm in using nonword stimuli if the SLP has specific reasons for doing so.

We can offer experimental prospective evidence on this topic from my lab however. It is also limited in that it involves only two children but they were both treated with a single subject randomization design that provides excellent internal validity. This study was conducted by my former student Dr. Tanya Matthews with support from Marla Folden, M.Sc., S-LP(C). The interventions were provided by McGill students in speech-language pathology who were completing their final internship. The two children presented with very different profiles: TASC02 had childhood apraxia of speech with an accompanying cognitive delay and ADHD. TASC33 presented with a mild articulation delay and verbal and  nonverbal IQ within normal limits.

Both children were treated according to the same protocol: they received 18 treatment sessions, provided 3 per week for 6 weeks. Each week they experience three different treatment conditions, randomly assigned to one of the 3 sessions and a unique target as shown in the table below for the two children. Each session consisted of a preprepractice portion and a practice portion. The prepractice was either Mixed Procedures (auditory bombardment, error detection tasks, phonetic placement, segmentation and chaining of segments with the words) or Control (no prepractice). In all three conditions practice was high intensity practice employing principles of motor learning.

realword vs nonword conditions

Random assignment of condition/target pairs to sessions within weeks permits the use of resampling tests to determine if there are statistically significant differences in outcomes as a function of treatment condition. Outcomes were assessed via imitation probes that were administered at the end of each treatment session to measure generalization to untreated items (same day probes) and probes that were administered approximately 2 days later (at the beginning of the next treatment session) to measure maintenance of those learning gains (next day probes). The next table shows the mean probe scores by condition and child, the test statistic (squared mean differences across conditions) and the associated p value for the treatment effect for each child.

realword vs nonword outcomes

The data shown in this table reveal no significant results for either child for same day or next day probe scores. In other words there was no advantage to the prepractice versus no prepractice condition and there was no advantage to nonword practice over real word practice.

We hope to publish some data soon that suggests that the specific type of prepractice might make a difference for certain children. But overall the most important driver of outcomes for children with speech sound disorders seems to be practice and lots of it.

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