Speech Therapy and Speech Motor Control: Part 3

In two previous blogs I discussed a recent paper by Strand in which she outlines in detail the theoretical foundation and procedural details of Dynamic Temporal and Tactile Cueing (DTTC) as a treatment for Childhood Apraxia of Speech (CAS). In Part 1 I suggested that the theoretical base, being Schmidt’s “Schema Theory of Discrete Motor Skill Learning,” was outdated. In Part 2 I discussed modern theories of speech motor control that assume a dynamic interplay of feedforward and feedback control mechanisms. In this blog I will discuss the implications for speech therapy, in relation to critical aspects of DTTC.

First, let us consider the core element of DTTC, “the focus on the movement (rather than the sound or phoneme) in terms of modeling, cueing, feedback, and target selection” (p. 4). I believe that all of us who strive to help children with CAS acquire intelligible speech agree that speech movements are the focus of speech therapy, as opposed to phonological contrasts. Nonetheless, this statement raises questions about the nature of “speech movements.” What is the goal of a speech movement? The answer to this question is controversial: it may be a somatosensory target involving specific articulators, such as for example bring the margins of the tongue blade into contact with the upper first molars; or it may be to produce a particular vocal tract shape such as a large back cavity separated from a small front cavity by a narrow constriction; or it may be to produce an acoustic output that will be perceived as the vowel [i]. The DTTC is structured to promote precise and consistent movements of the articulators and therefore the first scenario is presumed. Furthermore, the origin of CAS is hypothesized to be a deficit in proprioceptive processing that arises from an impairment in cerebellar mechanisms. Updating the theory, this hypothesis would implicate feedforward control which, following from Guenther and Vladosich (2012), “projects directly from the speech sound map [in left ventral premotor cortex and posterior Broca’s area] to articulatory control units in cerebellum and primary motor cortex” (p. 2). However, new research (Liégeois et al., 2019) identifies the locus of structural and functional impairments underlying CAS as being along a dorsal pathway of cortical structures, specifically: reduced white matter and fMRI activations in sensory motor cortex and along the arcuate fasciculus and reduced grey matter and fMRI activations in superior temporal gyrus and angular gyrus. They explain that “this route links auditory input/representation to articulatory systems … and transforms phonological representations into motor programs …In contrast, the speech execution white matter pathway (corticobulbar) and the ventral language route (IFOF) were not altered in this family” [that showed multigenerational impairments in speech praxis]. My point is that although the cerebellum is important to speech motor control and CAS may well involve impairments in proprioceptive feedback, speech is clearly a sensory motor skill that requires close connection among articulatory and auditory representations for sounds and syllables.

In Part 2 of this blog series I indicated that adults can compensate for unexpected perturbations to articulatory trajectories or auditory feedback very rapidly by drawing on their internal model of vocal tract function. It is interesting to consider that throughout speech development children cope with perturbations to articulatory gestures and expected acoustic outputs because their vocal tract is changing shape, sometimes quite dramatically, throughout childhood. Callen et al. (2000) showed how the developing child can adapt to the changing vocal tract by aiming for relatively stable auditory targets (conceived of as regions in auditory space) and using auditory feedback and simulations of auditory outputs to achieve those targets even as vocal tract structure is changing. The key to this remarkable ability is a learned mapping between articulator movements, vocal tract shapes and auditory outputs. The learning and updating of this internal model of vocal tract function arises from an unsupervised learning mechanism, essentially Hebbian learning: young infants engage in a great deal of unstructured vocal play as well as somewhat more structured babbling – speech practice that allows them to learn the necessary correspondences without having specific speech goals. Infants with CAS are widely believed to skip this period of speech development; therefore, it is likely they begin speech therapy without an internal model of vocal tract function which is foundational for goal directed speech practice. Therefore, precise, repeated, consistent speech movements may not be the best place to start a treatment program for severe CAS; a program of unstructured vocal play that targets highly varied playful vocalizations is a better starting place for many children. Subsequently, high intensity practice with babble (repetitive syllable production) will stabilize the mappings between articulatory gestures and the resulting vocal tract configurations and somatosensory and auditory outcomes.

One of the advantages of a well-tuned internal model of vocal tract function is that it supports “motor-equivalent speech production” given commonly occurring constraints on speech production. In other words, there are many different articulatory gestures that will produce the same acoustic-phonetic goal. When the child has a stable acoustic-phonetic target and is able to process auditory feedback in relation to that target, various articulatory solutions can be found to adapt to changing vocal tract structure or constraints such as talking while eating or a holding a pen between the teeth. Developmental changes in the way that articulators are coordinated to produce the same phoneme are well documented in the literature. Similarly speech production varies with phonetic context. Motor equivalent trading relations between tongue body height and lip rounding are well known for production of the vowel [u] and the consonant [ʃ] for example and the front-back positioning of the constriction in these phonemes is highly variable across speakers and phonetic contexts. The precision with which these phonemes are produced is related to the talker’s perceptual acuity: for example, adults who have sharp perceptual boundaries between [ʃ] and [s] produce them with greater articulatory consistency as well as greater acoustic contrast between the phoneme categories. Perkell et al. (2004) speculated “In learning to maximize intelligibility, the child with higher acuity is better able to reject poor exemplars of each phoneme (as in the DIVA model), and thus will adopt sensory goals for producing those phonemes that are further apart than the child with lower acuity.” The implications for speech therapy are that, even in the case of CAS, ensuring stable acoustic-phonetic targets for speech therapy goals is essential whereas insisting upon SLP defined articulatory parameters may be counter-productive. The goal is not absolute  consistency in the production of specific motor movements, but rather, dynamic stability in the achievement of speaking goals.

Although it is speculated that feedforward control is weighted more heavily than feedback control in adult speech, feedback is critical to speech learning during infancy and childhood. Furthermore, auditory feedback plays a crucial role. The initial goal is an auditory target. Guenther and Vladusich (2012) explain that “the auditory feedback control subsystem [helps to] shape the ongoing attempt to produce the sound by transforming auditory errors into corrective motor commands via the feedback control map in right ventral premotor cortex” (p. 2). They further explain that repeated practice of this type eventually leads to the development of somatosensory goal regions. A particular frustration for children with CAS is perseveration, the difficulty of changing a well-learned articulatory pattern to a new one that is more appropriate. This problem with perseveration highlights the need to engage the feedback control system. There are two strategies that are essential: first a high degree of variation in the practice materials which can be introduced by practicing nonsense syllables with a carefully graded increase in difficulty but variation in the combination of syllables within difficulty levels. The second strategy is to provide just the right amount of scaffolding along the integral stimulation hierarchy so that the child will be successful more often than not while experiencing a certain amount of error. Some error ensures that corrective motor commands will be generated from time to time. Imagine practicing syllables that combine four consonants [b, m, w, f] with four vowels [i], [u], [æ], [ɑ] and four diphthongs [ei], [ou], [ɑi], [au], [oi], presented at random so that the child imitates the first syllable (Say [bi]) and then repeats it again twice (Say it again… and again…), before proceeding to another syllable. You will have a great many targets in your session but created from a small number of elements. Imagine further that you progress to a more difficult level (reduplicated syllables, [bubu], [mimi]) as soon as the child achieves 80% correct production of the single syllables. You can see that you will also be allowing the child to produce quite a bit of error. We call this the challenge point. Tanya Matthews, Francoise Brosseau-Lapré and I are working on a paper to describe how to do this and describe our experiences with the approach. You will see that it is very different from working on five words and requiring that the child achieve 15 to 20 correct productions at the imitative word level before proceeding to delayed imitation and then again before proceeding to spontaneous productions. Errorless learning is a fundamental aspect of DTTC and has a long history in speech therapy practice. However it is not clear that it is well-motivated from the perspective of developmental science.

To summarize, there are many aspects of DTTC that are similar across all sensory-motor approaches to the treatment of CAS. In particular high intensity speech practice is well motivated and likely to be effective with all forms of moderate and severe speech sound disorder. Nonetheless there are some significant differences between Strand’s approach and the approach that I recommend based on an updated theory of speech motor control. There is still a great deal of research to do because very few of our specific speech therapy practices have received empirical validation even though speech therapy in general has been shown to be efficacious. As a guide to future research (hopefully using randomized and thus interpretable designs), I provide a table of procedures that are similar and different across the two theoretical approaches.

 

SCHEMA THEORY

AUDITORY FEEDBACK CONTROL

Treatment Procedures that are Similar

High intensity practice
Focus on speech movements (not phonemes)
Practice syllable sized units (not isolated sounds)
Attend to temporal aspects of trial structure (delayed imitation, delayed provision of feedback)
Integral stimulation hierarchy (attend to visual and auditory aspects of target)

Treatment Procedures that are Different

Focus on precise, consistent movements Focus on dynamic stability
Over-practice: accuracy over 10-20 trials Variable practice when possible
Errorless learning Challenge point: 4/5 correct, then move up
Behavioral shaping of accurate movements Motor equivalent movements
Tactile and gestural cues to ensure accuracy Sharpen knowledge of auditory target
“Hold” initial configurations Encourage vocal play, develop internal model

Readings:

Callan, D. E., Kent, R. D., Guenther, F. H., & Vorperian, H. K. (2000). An auditory-feedback-based neural network model of speech production that is robust to developmental changes in the size and shape of the articulatory system. Journal of Speech, Language, and Hearing Research, 43, 721-738.

Guenther, F. H., & Vladusich, T. (2012). A neural theory of speech acquisition and production. Journal of Neurolinguistics, 25(5), 408-422.

Liégeois, F. J., Turner, S. J., Mayes, A., Bonthrone, A. F., Boys, A., Smith, L., . . . Morgan, A. T. (2019). Dorsal language stream anomalies in an inherited speech disorder. Brain, 142(4), 966-977.

Perkell, J., Matthies, M., Lane, H., Guenther, F. H., Wilhelms-Tricarico, R., Wozniak, J., & Guiod, P. (1997). Speech motor control: Acoustic goals, saturation effects, auditory feedback and internal models. Speech Communication, 22, 227-250.

Perkell, J., Matthies, M. L., Tiede, M., Lane, H., Zandipour, M., Marrone, M., . . . Guenther, F. H. (2004). The distinctness of speakers’ /s/-/ʃ/ contrast is related to their auditory discrimination and use of an articulatory saturation effect. Journal of Speech, Language, and Hearing Research, 47, 1259-1269.

Rvachew, S., & Matthews, T. (2017). Demonstrating treatment efficacy using the single subject randomization design: A tutorial and demonstration. Journal of Communication Disorders, 67, 1-13.

Rvachew, S., & Matthews, T. (2019). An N-of-1 Randomized Controlled Trial of Interventions for Children With Inconsistent Speech Sound Errors. Journal of Speech, Language, and Hearing Research, 62, 3183–3203

Speech Therapy and Speech Motor Control: Part 2

Speech Therapy and Theories of Speech Motor Control: Part 2

In Part 1 of this blog series I described the theoretical basis of Dynamic Temporal and Tactile Cueing as recently published by Edy Strand. Specifically, the treatment is founded on Schmidt’s Schema Theory in which generalized motor programs are learned. During speech production the child must select the right program and apply the correct parameters before implementing it all at once. If the parameters are selected incorrectly, a speech error will occur. It is rather like making toast. If you forget to reset your settings after toasting bagels, your Wonderbread will come out black! The problem as stated by Schmidt is that by the time you realize that your toast settings are wrong and your motor gestures are off track, it’s too late— the toast is burned and you have said “Trat! Doast!” Learning occurs by “trial and error” — after much experience with your toaster you learn the settings (parameters) for getting the right amount of toastiness for different items. Learning to operate your toaster is similar to acquiring one “generalized motor program.” Speech motor learning is assumed to operate this way because sensory feedback is too slow to support on-line adjustments to the parameters in a direct way. I used a different analogy in the previous blog — once you have committed to swinging your golf club, you tend to follow through.

The problem with this model of speech motor control is that we know for certain that real time modification of vocal tract movements occurs in response to somatosensory and auditory feedback. Strangely we have known since the early eighties that the speech system is highly sensitive to error on-line; therefore, I don’t know why this idea of open-loop control persists. The proof comes from studies in which (typically) an adult is asked to repeatedly produce a particular syllable or disyllable and then experiences a perturbation in sensory feedback (either somatosensory feedback or auditory feedback). An early example of this paradigm involved productions of “aba”: during 15% of trials a mechanism placed an unexpected load on the talker’s lower lip. Here is where it gets interesting: the research participants corrected for this perturbation in the articulatory trajectory of the bottom lip very rapidly with compensatory actions of the top and the bottom lip (the bottom lip would need to exert greater upward force and the top lip would need to produce greater downward extent in order to produce the labial closure and the expected transitions into and out of the consonantal closure). Decades of experiments have followed involving many other perturbations in the domain of articulatory gestures, somatosensory (skin) sensations, and auditory feedback. For example, while the research participants are repeatedly saying “bed” you can trick their ear into thinking they are saying “bad” which leads to compensatory adjustments in articulation to get the expected auditory percept.

This kind of dynamic compensation across the entire vocal tract is made possible by an “internal model” — a neural model that simulates the behavior of a sensorimotor system in relation to its environment. The internal model can generate a prediction of the sensory consequences of implementing a motor plan via simulation. For speech, future outputs in the somatosensory and auditory domains are simulated; furthermore, the simulator takes into account delayed sensory feedback, noise in the perceptual system and other variables so that when feedback arrives it can be compared with the prediction and provide reliable error messages. Continuous tracking of the vocal tract state is thus permitted and forms the basis for ongoing planning of movements as speech unfolds. If an unexpected event occurs, as in the perturbation experiments that I have described, error corrections are dynamic across the entire system; therefore, if the predicted trajectory of acoustic formant transitions from the [a] into the [b] closure is not occurring, lower lip, upper lip, jaw and tongue movements can all be harnessed to produce the desired outcome.

As Houde and Nagarajan (2011) explain, “speech motor control is not an example of pure feedback control or feedforward control” (p. 11). The acquisition of speech motor control is dependent upon the development of the internal model of vocal tract function as well as detailed knowledge of auditory targets. This understanding has implications for the treatment of childhood apraxia of speech. I will explore these implications further in the next and final blog in this series.

Readings

Abbs, J. H., & Gracco, V. L. (1983). Sensorimotor actions in the control of multi-movement speech gestures. Trends in Neurosciences, 6, 391-395.

Houde, J. F., & Jordan, M. I. (2002). Sensorimotor adaptation of speech I: Compensation and adaptation. Journal of Speech, Language & Hearing Research, 45(2), 295-310.

Houde, J. F., & Nagarajan, S. S. (2011). Speech production as state feedback control. Frontiers in Human Neuroscience, 5, doi: 10.3389/fnhum.2011.00082.

Tourville, J. A., Reilly, K. J., & Guenther, F. H. (2008). Neural mechanisms underlying auditory feedback control of speech. NeuroImage, 39, 1429-1443.

Feedback Errors in Speech Therapy

I have been spending hours reviewing video of student SLPs (SSLPs) conducting speech therapy sessions, looking for snippets to take to my upcoming talks at ASHA2018. The students are impressively skilled with a very difficult CAS population but after this many hours of watching, repeated examples of certain categories of errors pile up in the provision of feedback to children about their attempts to produce the targets words, phrases and sentences. I am going to provide some examples here with commentary. In no way am I meaning any disrespect to the students because it is my experience that the average person becomes an idiot when a camera is pointed at them. I recall hearing about studies on the “audience effect” as an undergraduate – the idea is that when your skills are shaky you get worse when someone is watching but when your skills are excellent an audience actually enhances them. My social psychology prof said this even works for cockroaches! I can’t vouch for that but it certainly works for speech pathologists. I remember one time video-taping a session that was required for a course – I thought it went really well so I gave a copy to the parents and the course instructor. Later when watching it I could see clearly that for the whole half hour the child was trying desperately and without success to tell me that I was calling him by the wrong name (I had mixed him up with his twin brother whom I was also treating). I was oblivious to this during the live session but it was clear on the video. Anyway, these examples are not reflections on the students’ skill levels overall but they are examples of common feedback errors that I see in novice and experienced SLPs. Interestingly the clinical educators (CEs) who were supervising these sessions rarely mentioned this aspect of the students’ practice. Readers may find this blog useful as a template for reviewing student practice.

Category 1: No feedback

Child: [repeats 5 different sentences containing the target /s/ cluster words]

SSLP: [Turns to CE.] “What did you get?” [This is followed by 1 minute and 40 seconds of conversation about the child’s level of accuracy and strategies to improve it on the next block of trials.]

SSLP: [Turns back to child.] “You need to sit up. You got 2 out 5 correct. Now we’re going to count them on my fingers…”

Child: “Do we have to say these?”

Comment on vignette: In this case the SSLP did finally give feedback but too late for it to be meaningful to the child and after the telling the child off for slouching in her chair! Other variants on this are taking notes about the child’s performance or turning to converse with the child’s parent or getting caught up in the reinforcement game and forgetting to provide feedback. In CAS interventions it is common to provide feedback on a random schedule or to provide summative feedback after a block of trials. However, the child should be able to predict the block size and have information about whether their performance is generally improving or not. Even if the child does not have a count of number or percent trials correct, the child should know that practice stimuli are getting more difficult, reflecting performance gains. Sometimes, we deliberately plan to not provide feedback because we want the child to evaluate his or her own productions, but in these cases the child is told beforehand and the child is given a means of explicitly making that judgment (e.g., putting token in jar). Furthermore, the SSLP would be expected to praise the child for making accurate self-judgments or self-corrections. When the child does not get feedback or cannot track their own progress they will lose interest in the activity. It is common for SSLPs to change the game thinking that it is not motivating enough but there is nothing more motivating than a clear sense of success!

Possible solutions: Video record sessions and ask students to watch for and count the frequency of events in which the child has not received expected feedback. Provide child with visual guides to track progress indexed either as correct trials or difficulty of practice materials.

Category 2: Ambiguous feedback

SSLP: “Say [ska].”

Child: “[skak]”

SSLP: “OK, take the fish out.”

Comment on the vignette: In this case it is not clear if the SSLP is accepting the inexact repetition of her model. In our CAS interventions we expect the child to produce the model exactly because metathesis and other planning errors are common and therefore I would consider this production to be incorrect. Other ambiguous feedback that I observed frequently were “Good try” and “Nice try” and similar variants. In these cases the child has not received a clear signal that the “try” was incorrect. Another version of ambiguous feedback is to comment on the child’s behavior rather than the child’s speech accuracy (e.g., “You did it by yourself!” in which case the “it” is ambiguous to the child not clearly related to the accuracy of the child’s speech attempts).

Possible solutions: SSLPs really do not like telling children that have said something incorrectly. Ask students to role play firm and informative feedback. Have the students plan a small number of clear phrases that are acceptable to them as indicators of correct and incorrect responses (e.g., “I didn’t hear your snake sound” may be more acceptable than “No, that’s wrong”). Post written copies of the phrases somewhere in the therapy room so that the SLP can see them. Track the use of vague phrases such as “nice try” and impose a mutually agreed but fun penalty for exceeding a threshold number (buy the next coffee round for example). This works well if students are peer coaching.

Category 3: Mixed signals

SSLP: “Say [ska].”

Child: “[s:ka]”

SSLP: “Good job! Take the fish out.” [Frown on face].

Comment on the vignette: I am rather prone to this one myself due to strong concentration on next moves! But it is really unhelpful for children with speech and language delays who find the nonverbal message much easier to interpret than the verbal message.

Possible solutions: It would be better if SLP therapy rooms looked like a physiotherapy room. It annoys the heck out of me when we can’t get them outfitted with beautiful wall to ceiling mirrors. The child and SLP should sit or stand in front of the mirror when working on speech. Many games can be played using ticky tack or reusable stickers or dry erase pens. The SLP will be more aware of the congruence or incongruence between facial expressions, body language and verbal signals during the session.

Category 4: Feedback that reinforces the error

SSLP: “Repeat after me, Spatnuck” [this is the name of a rocket ship in nonsense word therapy].

Child: “fatnuck”

SSLP: “I think you said fatnuck with a [f:] instead of a [s:].

Comment on the vignette: Some SSLPs provide this kind of feedback so frequently that the child hears as many models of the incorrect form as the correct form. This is not helpful! This kind of feedback after the error is not easy for young children to process. To help the child succeed, it would be better to change the difficulty level of the task itself and provide more effective support before the next trial. After attempts, recasting incorrect tries and imitating correct tries can help the child monitor their own attempts at the target.

Possible solutions: Try similar strategies as suggested for ambiguous feedback. Plan appropriate feedback in advance. Plan to say this when the incorrect response is heard: “I didn’t hear the snake sound. Let’s try just the beginning of the word, watch me: sss-pat.” And when “spat” is achieved, plan to say “Good, I heard spat, you get a Spatnuck to put in space.”

Category 5: Confused feedback

SSLP: “Oh! Remember to curl your tongue when you say shadow.”

SSLP: “Oh! You found another pair.”

Child: “It’s shell [sʷɛo].”

SSLP: “Oh! I like the way you rounded your lips. Where is your tongue? Remember to hide your tongue.”

SSLP: Oh! You remembered where it was. You found another pair.”

Child: “Shoes [sʷuz].”

SSLP: “Oh! I like the way you rounded your tongue.”

Comment on vignette: In this vignette the SSLP is providing feedback about three aspects of the child’s performance-finding pairs when playing memory, rounding lips when attempting “sh” sounds, and in some cases anterior tongue placement when attempting the “sh” sound as well. One aspect of her feedback that is confusing when watching the video is the using of the exclamation “Oh!” Initially it appeared to signal an upcoming correction but it became so constant that it was not a predictable signal of any kind of feedback and was confusing. The exclamation had a negative valence to it but it might precede a correction or positive feedback. The SSLP confused her feedback about lips and tongue and it was not clear whether she was expecting the child to achieve the correct lip gesture, the correct tongue gesture or both at the same time.

Possible solutions: This can happen when there is too much happening in a session. The CE could help the SSLP restructure the session so that she can focus her attention on one aspect of the child’s behavior at a time, like this: “I want you to name these five pictures. Each time I am going to watch your lips. When you are done you can put the pictures on the table and mix them up for our game later.” If the child rounds the lips each time, switch to focusing on the tongue. When the ten cards are on the table play memory, modeling the picture names. In this way the three behaviors (rounding lips, retracting tongue, finding pairs) are separated in time and the SSLP can focus attention on each one with care, providing appropriate feedback repeatedly during the appropriate intervals.

Category 6: Confused use of reinforcement materials

SSLP: “Repeat after me, [ska].”

Child: “[θak]”

SSLP: [ska]

Child: “[θak]”

SSLP: “OK, take the fish out.”

SSLP: “Repeat after me, [ska].”

Child: [ska]

SSLP: “There you got it, take the fish out.”

SSLP: “Repeat after me, [ska].”

Child: [ska]

SSLP: “Good, and the last one, [ska].”

Child: [ska]

SSLP: “That’s good, take the fish out.”

Comment on vignette: In this vignette the child cannot tell if he gets a fish for correct answers or wrong answers or any answer. It is even worse if the child has been told that he will get a fish for each correct answer. Sometimes a student will say “Everything was going fine, we were having fun and then he just lost it!” When you look at the video you see exchanges such as the one reproduced here leading up to a tantrum by the child. The SSLP has broken a promise to the child. They don’t forgive that.

Possible solutions: This one is hard because it is a classic rooky mistake. Experience is the best cure. Reducing the number of tasks that the SSLP must do simultaneously may help. Therefore, in the early sessions the CE might keep track of the child’s correct and incorrect responses for the SSLP and allow her to focus on managing the materials and the child’s behavior. SSLPs would never think of this but it is possible to let the child manage the reinforcement materials themselves in some cases. One of our favorite vignettes, reprinted on page 463 of DPD2e (Case Study 9-4) involved an error detection activity in which the child could put toy animals in the barn but only when the SSLP said the names of the animals correctly. The child had the toys in his hands throughout the activity. He would not put them in the barn unless the clinician said the words correctly and would get annoyed if she said them wrong, telling her “you have to say cow [kau]!” SSLPs can learn that it is not necessary to control everything.

I put these here for students and clinical educators and speech-language pathologists and hope that you will have fun finding these feedback mishaps in your own sessions. If you come up with better strategies to avoid them than I have suggested here please share them in the comments.

Testing Client Response to Alternative Speech Therapies

Buchwald et al published one of the many interesting papers in a recent special issue on motor speech disorders in the Journal of Speech, Language and Hearing Research. In their paper they outline a common approach to speech production, one that is illustrated and discussed in some detail in Chapters 3 and 7 of our book, Developmental Phonological Disorders: Foundations of Clinical Practice. Buchwald et al. apply it in the context of Acquired Apraxia of Speech however. They distinguish between patients who produce speech errors subsequent to left hemisphere cardiovascular accident as a consequence of motor planning difficulties versus phonological planning difficulties. Specifically, in their study there are four such patients, two in each subgroup. Acoustic analysis was used to determine whether their cluster errors arose during phonological planning or in the next stage of speech production – during motor planning. The analysis involves comparing the durations of segments in triads of words like this: /skæmp/ → [skæmp], /skæmp/ → [skæm], /skæm/ → [skæm]. The basic idea is that if segments such as [k] in /sk/ → [k] or [m] in /mp/ → [m] are produced as they would be in a singleton context, then the errors arise during phonological planning; alternatively, if they are produced as they would be in the cluster context, then the deletion errors arise during motor planning. This leads the authors to hypothesize that patients with these different error types would respond differently to intervention. So they treated all four patients with the same treatment, described as “repetition based speech motor learning practice”. Consistent with their hypothesis, the two patients with motor planning errors responded to this treatment and the two with phonological planning errors did not as shown in the table of pre- versus post-treatment results.

Buchwald et al results corrected table

However, as the authors point out, a significant limitation of this study is that the design is not experimental. Having failed to establish experimental control either within or across speakers it is difficult to draw conclusions.

I find the paper to be of interest on two accounts nonetheless. Firstly, their hypothesis is exactly the same hypothesis that Tanya Matthews and I posed for children who present with phonological versus motor planning deficits. Secondly, their hypothesis is fully compatible with the application of a single subject randomization design. Therefore it provides me with an opportunity to follow through with my promise from the previous blog, to demonstrate how to set up this design for clinical research.

For her dissertation research, Tanya identified 11 children with severe speech disorders and inconsistent speech sound errors who completed our full experimental paradigm. These children were diagnosed with either a phonological planning disorder or a motor planning disorder using the Syllable Repetition Task and other assessments as described in our recently CJSLPA paper, available open access here. Using those procedures, we found that 6 had a motor planning deficit and 5 had a phonological planning deficit.

Then we hypothesized that the children with motor planning disorders would respond to a treatment that targeted speech motor control: much like Brumbach et al., it included repetition practice according to the principles of motor practice during the practice parts of the session but during prepractice, children were taught to identify the target words and to identify mispronunciations of the target words so that they would be better able to integrate feedback and self-correct during repetition practice. Notice that direct and delayed imitation are important procedures in this approach. We called this the auditory-motor integration (AMI approach).

For children with Phonological Planning disorders we hypothesized that they would respond to a treatment similar to the principles suggested by Dodd et al (i.e., see core vocabulary approach). Specifically the children are taught to segment the target words into phonemes, associating the phonemes with visual cues. Then we taught the children to chain the phonemes back together into a single word. Finally, during the practice component of each session, we encouraged the children to produce the words using the visual cues when necessary. An important component of this approach is that auditory-visual models are not provided prior to the child’s production attempt-the child is forced to construct the phonological plan independently. We called this the phonological memory & planning (PMP) approach.

We also had a control condition that consisted solely of repetition practice (CON condition).

The big difference between our work and Brumbach et al. is that we tested our hypothesis using a single subject block randomization design, as described in our recent tutorial in Journal of Communication Disorders. The design was set up so that each of the 11 children experienced all three treatments. We chose 3 treatment targets for each child, randomly assigned the targets to each of the three treatments, and then randomly assigned the treatments to each of three sessions, scheduled to occur on different days of the week, 3 sessions per week for 6 weeks. You can see from the table below that each week counts as one block, so there are 6 blocks of 3 sessions for 18 sessions in total. The randomization scheme was generated blindly and independently using computer software for each child. The diagram below shows the treatment schedule for one of the children with a motor planning disorder.

Block Randomization TASC02 DPD Blog

This design allowed us to compare response to the three treatments within each child using a randomization test. For this child, the randomization test revealed a highly significant difference in favour of the AMI treatment as compared to the PMP treatment, as hypothesized for children with motor planning deficits. I don’t want to scoop Tanya’s thesis because she will finish it soon, before the end of 2017 I’m sure, but the long and the short of it is that we have a very clear results in favour of our hypothesis using this fully experimental design and the statistics that are licensed by it. I hope you will check out our tutorial on the application of this design: we show how flexible and versatile this design can be for addressing many different questions about speech-language practice. There is much exciting work being done in the area of speech motor control and this is a design that gives researchers and clinicians an opportunity to obtain interpretable results with small samples of children with rare or idiosyncratic profiles.

Reading

Buchwald, A., & Miozzo, M. (2012). Phonological and Motor Errors in Individuals With Acquired Sound Production Impairment. Journal of Speech, Language, and Hearing Research, 55(5), S1573-S1586. doi:10.1044/1092-4388(2012/11-0200)

Rvachew, S., & Matthews, T. (2017). Using the Syllable Repetition Task to Reveal Underlying Speech Processes in Childhood Apraxia of Speech: A Tutorial. Canadian Journal of Speech-Language Pathology and Audiology, 41(1), 106-126.

Rvachew, S., & Matthews, T. (2017). Demonstrating treatment efficacy using the single subject randomization design: A tutorial and demonstration. Journal of Communication Disorders, 67, 1-13. doi:https://doi.org/10.1016/j.jcomdis.2017.04.003

 

AOS, CAS and STM

I greatly enjoyed this new Frontiers in Neuroscience paper by Hickok and colleagues called “Partially overlapping sensorimotor networks underlie speech praxis and verbal short-term memory: Evidence from apraxia of speech following acute stroke”. These researchers evaluated 76 patients during the acute phase of their stroke using behavioral and MRI measures. They found a strong relationship between apraxia (AOS) and verbal short- term memory (vSTM) difficulties as well as weak relationships between aphasia and AOS and vSTM upon behavioral testing. For patients with AOS, the MRIs revealed tissue damage along a sensorimotor network of motor-related areas and sensory-related areas. The motor related areas that were implicated were as follows: primary motor cortex (proposed site of motor programs for opening and closing vocal tract gestures that correspond roughly to consonant and vowel phonemes); pars opercularis (a part of Broca’s area involved in phonological processing and suppression of response tendencies);  premotor cortex (planning and sequencing of speech units and sensory guidance of movement; motor programs for syllables); and insula (specialized for motor planning of speech). The sensory-related areas  associated with AOS were primary somatosensory cortex (site of  somatosensory targets for speech); secondary somatosensory cortex (sensorimotor integration); parietal operculum (sensory motor interface for speech); and auditory cortex (processing of auditory information; auditory targets for speech). The areas associated with vSTM deficits overlapped those associated with AOS but only in the motor-related areas, specifically pars opercularis and par triangularis (i.e., Broca’s area), premotor cortex and primary motor cortex.

With regard to the network associated with AOS, the authors concluded that the findings demonstrate “that the targets for speech are sensory in nature” and that “motor control generally and speech motor control specifically is dependent on sensorimotor integration”. I found these conclusions to be interesting in view of our interventions studies with children who have childhood apraxia of speech. As I reported in a previous blog, we are having success with an approach in which we encourage strengthening of both articulatory-phonetic and acoustic-phonetic representations for target words and the connections between them.

With regard to vSTM, the authors indicate that “the involvement of motor areas is predicted as vSTM involves an articulatory rehearsal component”. They seem  surprised however that “posterior, sensory related regions” were not implicated in this study as correlates of the hypothesized “storage” component in short-term memory. This finding reminded me of a paper I wrote in 2008 in which I pointed out that children’s nonword repetition performance, supposedly a measure of vSTM, factors with speech production accuracy rather than language ability in large scale studies involving children with either typical or atypical language development. I interpreted these findings in relation to a connectionist model of working memory proposed by MacDonald and Christensen (2002). According to this model there is no short term memory store per se because  working memory is not differentiated from linguistic knowledge and processing. Individual differences in working memory task performance reflect differences in precision of phonological representations and processing efficiency due to experiential and biological factors. The processes and representations involved in working memory are the same as those used in speech planning.  Many of the children that we are working with have difficulty planning an utterance – I have described these children with phonological planning difficulties in a previous blog. The children have difficulty with consistent repetition of nonwords and complex real words. The successful intervention for these children involves providing multimodal external cues to support the child’s efforts to construct and execute a plan to produce new words, as described in a previous blog. It is important that the SLP avoid providing an auditory  model for imitation by the child however although the SLP may imitate the child’s production to reinforce successful attempts or correct failed attempts.

Hickok et al interpret their findings in light of their hierarchical model although I remain uncertain about this notion of a hierarchical organization of these components just because I can never quite sort out what ‘higher” versus “lower” means when placing these kinds of components in a hierarchical relationship.  The importance of acquiring knowledge of different forms of linguistic representation – acoustic, articulatory, phonological and semantic – and linking across multiple representations to achieve functional goals has implications for typical and atypical language development however.

Tanya and I will be discussing these issues further (with video demonstrations) at ASHA2014:

Topic Area: Speech Sound Disorders in Children Session Number: 1037 Title: Differential Diagnosis of Severe Phonological Disorder & Childhood Apraxia of Speech Session Format: Seminar 2-hours Day: Thursday, November 20, 2014 Time: 10:30 AM ─ 12:30 PM Author(s): Susan Rvachew and Tanya Matthews

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).

Image

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.

 

 

 

Auditory Motor Integration Intervention for CAS

In March 2013 I described the research we are conducting in my lab to identify individual differences in response to two different approaches to the treatment of Childhood Apraxia of Speech. I also described the unique single subject randomization design that we are using and presented some data for one child without revealing the interventions that corresponded to the condition that worked best for this particular child. We have subsequently replicated this result with another child so today I am going to write about the features of the intervention that children with difficulties in the area of transcoding appear to benefit from most clearly. Recall that transcoding is revealed in part by addition errors on the Syllable Repetition Task. In the case of the child profiled in the previous blog, he added nasal consonants at syllable boundaries when asked to repeat the syllable strings and he was just as likely to do this for short strings as for long, e.g., “mada” → [bᴂndə] and “manabada” → [mandabad]. This child also had difficulty with multisyllable repetition during the maximum performance tests but no difficulty with the single syllable diadochokinetic rate. Within word inconsistency was borderline with inconsistent word productions largely reflecting single feature errors (voicing errors for example). Altogether the impression is of a true apraxia or motor planning disorder (as opposed to a phonological planning deficit, a more common problem that I will describe in a future post). Thus far we have assessed 18 children in this study and remarkably only 3 have presented with this particular profile.

Two of these children have shown the best response to an intervention that is directed at promoting auditory-motor integration. It includes input-oriented procedures that are described in Chapter 9 of my book combined with output-oriented procedures described in Chapter 10. The procedures are used to promote the consistent use of stimulable phonemes in the context of word shapes that are difficult for the child so that the focus is more on holistic movement patterns at the whole word level than on individual phonemes. In the case described here we taught novel “monster names” that had a strong-weak-strong stress pattern and word internal coda consonants such as “Biftenope” and “Hapnidreem” and assessed for carry-over to phrases with similar structures (pumpkin pie, bat mobile). 

One reason that we designed an intervention approach that focused on auditory-motor integration is that there is evidence from the animal literature suggesting that this might be a foundational problem in the case of apraxia. Kurt, Fisher and Ehret examined sensory-motor association learning in mice with two different FoxP2 mutations. The task involved learning to avoid electronic shock by leaping a hurdle (or not) to the other compartment of a box in response to varied tones that signaled the location of the shock. Mice with either mutation were impaired in their response, one more severe that the other, in comparison to wild-type mice that learned the task without difficulty. The second reason that we designed an intervention with an auditory-motor integration component is that the ability to modify motor plans in response to auditory feedback and in relation to an auditory target is theoretically essential to the acquisition of speech motor control.

So what does an intervention that focuses on auditory-motor integration look like? Not surprisingly it has procedures that focus attention on the auditory-perceptual aspects of speech as well as procedures that focus on motor practice, none of the procedures themselves being novel or surprising. During the prepractice portion of each treatment we ensured that the child had a good perceptual representation for the target words using auditory bombardment and focused stimulation in meaningful contexts as well as error detection tasks as described in my teaching blog (scroll down to week 22). We also taught the child to monitor his own speech and respond differentially to his own correct or incorrect productions of the target words. For example an appropriate activity might be for the child “call” the monster and to then place the monster in his sleeping bag in the tent if he heard himself produce the name correctly or to place the monster in an alternative sleeping bag out in the rain if he heard himself produce the name incorrectly (our students are endlessly creative and this variation on the game has proved to be popular with the children this year).  The practice part of the session, for the most part, proceeds as one would expect for any child with CAS, focusing on high intensity practice while the SLP provides just enough stimulation prior to each attempt to elicit a correct response more often than not. However, every effort is made to avoid providing too much feedback. Working in blocks of five trials each, summative knowledge of results is provided whenever possible – this means that the child is given an opportunity to evaluate his own responses in relation to his own auditory goal without interference from SLP input, and then compare his own judgment with the SLPs count of correct responses at the end of each 5 trial run. Edy Strand writes about the importance of giving the child time to integrate feedback in her chapter with Derbertine in Caruso and Strand (1999) and describes precisely how to do this. Given a high rate of responses (over 100 trials per 20 minute practice session) and an average of 70% correct responses, this child was able to make excellent progress as measured by both same day and next day probes (see green bars on his chart here). A second child with the same profile also showed a significant benefit in favour of this approach. A third child is still being treated and it will be some time before we will know if he completes the protocol and then many more months before blind coding of his results will be finished. But, we are hopeful!

Online Gaming and Speech Therapy

I have just read this marvelous paper tweeted out by @vaughanbell: Stafford, T., & Dewar, M. (2013). Tracing the Trajectory of Skill Learning With a Very Large Sample of Online Game Players. Psychological Science. He was impressed by the very large sample size (N = 854,064) but I am impressed by the relevance of this paper for speech therapy. The researchers used “detailed records of practice activity from an on-line game” and used it to test hypotheses about learning in the game which requires “rapid perceptual decision making and motor responses”. Gratifyingly for us as speech-language pathologists, the results confirm the principles of motor learning that are currently promoted for successful treatment of childhood apraxia of speech (CAS), specifically practice intensity, distributed practice and variable practice conditions (for application of these principles to the treatment of apraxia of speech see for example Gildersleeve-Neuman in the ASHA Leader or Tricia McCabe’s ReST program).

There was one concept raised in the paper that was a little bit novel with respect to the CAS literature however: specifically, the authors talk about the “exploration/exploitation” dilemma. In the context of this simple but bizarrely fun computer game (found here at The Welcome Collection)  you can explore the axon growing environment when first learning to play or you can settle into a strategy of simply clicking on the closest protein in your circle of influence. The latter strategy will work to grow your axon which is the object of the game but you will miss out on learning how to maneuver your circle of influence so as to actively find the “power proteins” that advance the growth of your axon. Exploration has a cost in that it leads to more variable performance early on but the benefit is potentially better performance with longer experience. In fact, Stafford et al. observed a close relationship between higher early variance in performance and better performance during later attempts. This trade-off between exploration and exploitation reminded me of the importance of the expansion stage in early speech development and the implications for intervention with young children with CAS.

In Table 10-1 of Developmental Phonological Disorders: Foundations of Clinical Practice we suggest learning outcomes and therapeutic strategies to correspond to four stages of speech development as follows: 1. Expansion stage (explore possibilities of the vocal system); 2. Babbling and integrative stage (controlled variability); 3. Early speech development (expanding repertoire of phones and word shapes to achieve intelligible speech); and 4. Late speech development (ongoing refinements to achieve adultlike speech accuracy and precision). These stages are described in greater detail in Chapter 3 which covers the literature on the development of speech motor control. The expansion stage typically occurs during months 3 through 6 and is characterized by a variety of vocalizations that are not very speech-like (squeals, growls, raspberries and so on) as well as the appearance of fully resonant vowels and marginal babble. It is my experience that SLPs do not appreciate the importance of the expansion stage to normal speech development or understand its significance when planning an intervention program for children with limited if any speech capacity. Therefore I highlight this point in Chapter 10, as follows:

“The importance of the expansion stage in the laying of building blocks for later speech development is easy to forget when choosing goals for speech therapy, a topic to which we return shortly. Another important achievement during the infant period is the acquisition of canonical syllables when the child learns to control the variable parameters explored during the expansion stage, coordinating them to produce well-formed syllables in the context of babble, jargon, and early words. …Typical descriptions of speech acquisition focus on reductions in variability with age. … Therefore, it is not surprising that traditional speech therapy procedures are designed to enhance consistency and reduce variability in the production of phonemes with practice. However, variability is not always an impediment to speech learning and children with DPD often suffer from insufficient variability in their repertoire of speech behaviors. Performance variability can be viewed as facilitating, detrimental, or irrelevant to a successful outcome depending on the motor learning context (Vereijken, 2010). For example, the highly variable vocalizations of the expansion stage provide a complex foundation for the emergence of speechlike vocalizations at later stages. Infants who are described as being “quiet” during the first year of life lack sufficient variability for normal motor speech development. The normally developing infant harnesses rather than reduces this variability to coordinate the separate respiratory, phonatory, resonance, and articulatory components to produce babble in the next stage. Throughout the next 16 or so years there will be a continual interplay between adaptive variability to meet new challenges and increased stability to enhance precision. (p. 758)”

 I often talk to SLPs who are frustrated by failed efforts to teach new phones via imitation to children with severe speech sound disorders. However children with limited vocal repertoires must first be encouraged to freely explore their vocal systems. I describe procedures to encourage vocal play in detail in the book, following Dethorne, Johnson, Walder, and Mahurin-Smith (2009) and supplementing with examples of implementation from my own clinical experience. I hope that Stafford et al.’s interesting research and this amusing little game leads to more reflection about the role of exploration and variability in speech motor learning.