Phonological Memory and Phonological Planning

I have been writing about the children in our intervention study for children with Childhood Apraxia of Speech (CAS). So far about half of the children referred to us appear to have difficulties in the domain of phonological memory with their overt phenotype corresponding to the subtype described by Dorothy Bishop Dodd as Inconsistent Deviant Disorder. Shriberg et al. (2012) have developed the Syllable Repetition Task as one means of identifying deficits in “memory processes that store and retrieve [phonemic, sublexical, and lexical] representations. We have been using this SRT test to differentiate children who have deficits in phonological planning versus motor planning. I described the profile that corresponds to difficulties with motor planning (transcoding) in a previous post. Today I will discuss the phonological memory or phonological planning profile that we see in approximately half of the children that are referred to us with suspected CAS.

These children can be identified by a qualitative analysis of their SRT performance and by their performance on the Inconsistency Test of the DEAP. Starting with the SRT, one child in our study for example was able to achieve 12/18 consonants correct when imitating 2-syllable items but only 5/18 consonants correct when imitating 3-syllable items, thus exemplifying the classic profile of a child with phonological memory difficulties – better nonword repetition performance for short versus long items. Qualitatively he tended toward consonant harmony errors even with some 2-syllable items, /bama/=[mama],  /maba/=[mama],  and then more frequently with the 3-syllable items, /nabada/=[mamada]. Addition of syllables and vowel errors also occurred, /manaba/ = [mamadada],  /manabada/=[mimadama]. Poor maintenance of phonotactic structure and vowel errors were also observed on the Inconsistency Test, “helicopter” = [hokopapɚ], “elephant”= [ɛmpɩnt], which yielded an overall inconsistency score of 78% as many words were produced with multiple variants, e.g., “butterfly”= [bʌtfaɩ], [bʌtwaɩ], [bʌtətwaɩ].

The most striking illustration of the difficulties these children have with the storage and retrieval of phonological representations comes during our treatment sessions however. In this research program we are teaching the children nonsense words in meaningful contexts. For example in one scenario we teach the children the names of “alien flowers” and in one of the treatment conditions we use graphic stimuli, paired with gestural cues if necessary, to represent the syllables and phonemes in the words and phrases that we are teaching. Many of the children in our study learn all of the nonsense words without difficulty (5 words per goal/condition introduced over 6 45-minute sessions). However children with the phonological memory difficulties have great difficulty learning the words (SLP: This is a speet. Say speet. Child: speet. That’s right, speet. What is it? Child: I don’t know. SLP: Yes, you do it’s speet, the purple one, the purple one is speet, remember, say speet. Child: ‘speet’. SLP, you’ve got it, the purple flower is speet, it’s a speet, what is it, it’s a … Child: um, I don’t know, and so on).

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The most effective intervention to use with these children closely mirrors the procedures described by Barbara Dodd as the “core vocabulary” approach and demonstrated by Sharon Crosbie in the video that accompanies their chapter in the Williams, McLeod and McCauley (2010) book. The video is lovely and shows how to use graphic stimuli and a chaining procedure to teach the child to produce a word consistently – the idea is to encourage the child to develop and implement their own phonological/motor plan rather than relying on an imitative model. The children respond to this technique really well and will learn to say the new words such as “speet” and “stoon” quickly and accurately. The trouble begins when our student SLPs want the children to use the new words spontaneously in phrases (e.g., “water the speet”). They have great difficulty remembering the word or even the carrier phrase without the imitative model and I have to work really hard to teach the student clinicians to withhold the imitative model in favour of using other cues to stimulate spontaneous production of the target words and phrases (SLP: What is it? Let’s start with the snake sound here…).

We have wonderful video of student SLPs learning these techniques as well as children achieving their goals. Tanya Matthews and I will be presenting them at ASHA 2014. The difference in the way that you implement therapy with these children is subtle but important. I am pretty sure that Case Study 8-4 in our book had a phonological planning deficit rather than the motor planning disorder that he was treated for. I can’t help but think that if he was treated with these techniques he might have made some progress in the three years that we followed his case (whereas he made literally no progress at all until he was treated with a synthetic phonics approach in second grade). I’d love to hear from you if you have any other ideas about how best to treat children with phonological memory problems and inconsistent deviant disorder.

 

 

 

Single Subject Randomization Design for CAS Intervention Research

I have recently returned from the very excellent Childhood Apraxia of Speech Symposium sponsored by the Childhood Apraxia of Speech Association of North America and held in Atlanta last month. The scientific presentations were wonderful and I hope to have posts related to many of them over the next few months. I begin by highlighting Larry Shriberg’s presentation as it relates to my current CASANA funded intervention study and I am, with some excitement, analyzing the data from the first cohort of participants this week since it is our winter break from teaching.

Dr. Shriberg presented data recently published in Clinical Linguistics and Phonetics (Shriberg, Lohmeier, Strand & Jakielski, 2012). In this paper the authors describe the use of the Syllable Repetition Task (SRT) for the identification of CAS. The paper, the test, and all the information you need for scoring and interpreting the test data is available for download at The Phonology Project website. The SRT consists of 18 items comprised of two to four syllables made up of the consonants /m, n, b, d/ and the vowel /ɑ/ and thus it is designed explicitly for children with speech delay. The task was administered to 4 quite large samples of children: Group 1, Typical Speech, Typical language; Group 2, Speech Delay, Typical Language; Group 3, Speech Delay, Language Impairment; and Group 4, CAS with this last group subdivided into idiopathic and neurogenetic etiological subtypes for some analyses. The test results were presented in the form of four scores: Competence, total percentage of correctly repeated consonants overall; Encoding Processes, percentage of within-class manner substitutions; Memorial Processes, ratio of sounds correct in 3-syllable-versus-2-syllable items; Transcoding processes, percentage of items containing one or more addition errors, subtracted from 100 for directional clarity. Most interestingly, the latter three scores were not correlated with each other within any of the groups although they were all moderately correlated with the competence score. The CAS group showed worse performance than the other three groups on all of these measures although their performance on the Transcoding processes measure was most distinctive. The diagnostic usefulness of the Transcoding score is much enhanced by also considering aspects of the children’s prosody in connected speech (inappropriate pauses, slow rate, lexical or phrasal stress errors). In conclusion, these findings were taken as evidence that CAS is a multiple domain disorder with low encoding scores reflecting incomplete or poorly formed phonological representations, low memorial scores reflecting difficulties with phonological memory, and low transcoding scores reflecting a motor planning/programming deficit. Given that the paper presents group data, and that the encoding, memorial and transcoding scores are not correlated with each other, it is not clear however that all children with CAS will show difficulties in all of these areas. It seems possible if not likely that there will be considerable heterogeneity within this population with different children showing variant profiles across these three speech processes. The purpose of our study is to consider this heterogeneity by examining response to three interventions in individual subjects.

In a previous post I mentioned an alternative to traditional single subject designs that does not require a stable baseline while allowing for statistical analysis. We are using one form of this design in this study, the single subject randomization design, more specifically set up as a randomized block experiment as described in my paper on the application of these designs to communication disorders research (Rvachew, 1988). We have six children participating in the study this winter and 3 more enrolled for the spring. I provide partial data for one child in this post simply as a way of demonstrating the usefulness of this design for research with low incidence disorders. The child is school age with borderline verbal and nonverbal IQ, speech delay, and ADHD. Apraxia of speech was confirmed by administration of the Kaufman Speech Praxis Test and maximum performance tasks revealing normal single syllable repetition rates but an inability to sequence three syllables consistently and at a normal rate. The results of the Syllable Repetition Task indicated an extremely low competence score despite encoding and memorial processing within the average range for his age. He did have difficulties with transcoding however as indicated by the characteristic addition of nasal consonants.

Three speech targets were selected for this boy: word internal codas, word-initial /l/ clusters, and word initial velar stops (with baseline performance in single word naming being 50, 29, and 33 percent correct respectively). All targets were addressed via pseudowords linked to nonsense referents in a functional context. All targets received 20 minutes of concentrated practice per week using the integral stimulation hierarchy as described by Christine Gildersleeve-Neuman. However, the prepractice condition (which was implemented for 20 minutes prior to the practice session) varied for each target. The three prepractice conditions being compared in this study were randomly assigned to the targets with the following result: word internal codas were treated using input oriented prepractice procedures, word-internal /l/ clusters were associated with sham prepractice procedures (control condition) and velar stops were treated with output oriented prepractice conditions. The input oriented prepractice conditions included auditory bombardment and error detection tasks as described by Rvachew and Brosseau-Lapre (see also Chapter 9 of our book, http://www.pluralpublishing.com/publication_dpd.htm). The output oriented procedures are described by Dodd and colleagues for improving the child’s ability to independently build a phonological plan for the word by linking syllables and phonemes to graphical cues and then chaining the subword units. Phonetic placement was also incorporated into this condition as needed.

Raw Session and Next Day Probe Scores for One Child By Treatment Condition

Raw Session and Next Day Probe Scores for One Child By Treatment Condition

In-keeping with the randomized block design, the child received three treatment sessions per week, with each treatment condition/treatment target pair assigned at random to one of the three days on a week by week basis. Two outcome measures were recorded: the child’s responses to imitative phrase probes that were administered at the end of the session to assess learning during a given intervention session, and the child’s responses to imitative phrase probes that were administered at the beginning of the next session to assess maintenance of learning. The child’s performance on these probes is shown on the figure below: pastel bars are the session probes indexing session performance and solid bars are the next day probes indexing maintenance of learning to the next session. Different colours represent different prepractice conditions. These probe scores were submitted to a nonparametric randomization test as described in Rvachew (1988) with the results indicating that there was no difference in probe performance at the end of each session as a function of prepractice condition, F(2,5) = 1.19, p = .392. However, there is a significant effect of prepractice condition when considering next day probe performance, F(2,5) = 23.01, p = .002. Now, I am going to make you crazy by not revealing which prepractice condition is associated with each colour! The reason is that this is just one child and I want to see the results for the other children –  I have observed the responses of the other children and have reason to believe that in fact there are differences in actual learning as a function of prepractice condition but we will feel more confident after having blinded transcriptions of probe data from more children. It should be obvious with this design that there are many other variables that can influence the outcome such as intrinsic differences in the difficulty of the targets, differences associated with the days of the week, and differences in clinician (although some of the same people were in the room during every session, the treating clinician was not the same during every session). Therefore we need to replicate the result many times before we feel confident interpreting these results. However, I wanted to introduce readers to the SRT, the notion of CAS as a multiple domain disorder, and the single subject randomization design as a way of looking at the relationship between response to intervention and underlying psycholinguistic profile. I hope that you will stay tuned – we hope to take data from the first six children to ASHA13.