Thinking about ‘Dose’ and SLP Practice: Part III

Continuing my discussion about the concept of ‘dose’ as applied to speech therapy, I finally get to the heart of the matter which is the issue of the optimal ‘dose’ of speech therapy to achieve the desired outcome which in our context is generalization of a phonology goal to untreated words. In previous blogs I discussed the definition of ‘dose’ in terms of the number of effective teaching episodes and the need to identify the effective ingredients of your intervention beyond the therapeutic alliance. Here I will discuss ‘dose’ specifically, as in how many effective teaching episodes are enough to achieve a good outcome in phonology intervention?

Let’s begin by returning to the pharmacology context from which the concept of dosage is borrowed. How is the concept helpful to physicians? First, it is important to know the optimum dose (or dose range) for average patients so as to avoid harming the patient. If the prescribed dose is too low the patient may not improve and the continuance or worsening of symptoms and disease will be harmful for the patient. If the dose is too high the medication itself may be toxic and harm the patient directly. Second, the patient’s response to the medication is diagnostic. If the maximum safe dosage has been prescribed and the patient is not responding favorably the physician must seek the reason: Is the patient complying with the prescribed treatment regimen? Is the patient doing something else that interferes with the effectiveness of the medication? Is the health care system administering the dose as prescribed? Does this patient respond to medications in an individualized fashion, such that a switch to another medication is required? Is the diagnosis wrong such that an entirely different treatment is called for? I will describe the research on appropriate dose in the case of meaningful minimal pairs therapy (applied to preschool aged children with moderate or severe phonological disorders) and we can consider whether these questions are relevant in the speech therapy context.

The method of meaningful minimal pairs is a uniquely linguistic approach to therapy that has the goal of changing the child’s production of an entire sound class. The procedure has two key components: (1) teaching the child pairs of words that differ by a single phoneme; and (2) arranging the environment so that the child experiences a communication breakdown if both words in a  pair are produced as a homophone. (SLPs and researchers usually get the first part right but often forget the second!) The method is directed at the child’s phonological knowledge and therefore should not be applied until after phonetic knowledge of the contrasting phonemes in the perceptual and articulatory realms has been established.

There is a lot of research involving this method and at least two papers have carefully documented the dose that leads to generalization from trained to untrained words/targets. More than 50% generalization is the outcome of interest because we know from other studies that you can discontinue direct treatment on the target pattern at this point and the child will continue to make spontaneous gains. The two papers that I will discuss have the further benefit of allowing the reader to count the “dose” precisely as the number of practice trials. The papers also provide information about the number of sessions and the number of minimal pairs over which the practice trials were distributed.

Weiner (1981) demonstrated that the method was effective with two children, using a multiple baseline design and treating deletion of final consonants (DFC), stopping of fricatives (ST) and fronting (F). Four minimal pairs were taught per target pattern and use of the pattern was probed continuously for treatment words and on a session-by-session basis for generalization words. The results do not show that much difference across target patterns but the response across children was markedly different with one child showing much faster progress than the other for all targets. For example, Child A reduced DFC to below 50% in treated words after 120 practice trials and in generalization words after 300 trials. On the other hand, Child B required 200 and 480 trials respectively to reach the same milestones for DFC. Furthermore Child A was able to accomplish many more trials in a session (e.g., 400 practice trials over 5 sessions for child A or 80 trials/session vs. 570 practice trials over 13 sessions or 43 trials/ session for child B). Despite this large variance in rate of progress across children, the study suggests that an SLP should expect a good treatment response with this method after no more than 500 trials.

This finding was replicated in a larger sample (n = 19) by Elbert, Powell and Swartzlander (1991). In this study a behaviorist approach was taken to the treatment of the minimal pair words in contrast to Weiner’s procedure that emphasized the communication breakdown as an important part of the procedure. The children were taught one pair at a time in series and the study was structured to determine how many children would achieve generalization to untreated words ,at a level of at least 50%, after learning 3, 5 or 10 pairs of words. They found that 59% of the children generalized after learning 3 pairs which took an average of 487 practice trials (range 180 to 1041) administered over approximately 5 20-minute treatment sessions; 21% of children needed to learn 5 word pairs (1221 practice trials on average) and 14% needed to learn 10 words pairs (2029 practice trials on average) before generalization occurred. This left 7% of children who did not generalize at all.

How can we use these data about dosage in our treatment planning? There is a lot of useful information here. First, we know that it is possible to achieve 80-100 practice trials in 20 minutes. Therefore, if your treatment sessions are 20 minutes long you can target one phonological pattern and if they are 60 minutes long you can target 3. Second, they show us that children do not usually generalize in under 180 practice trials (and I would argue that the data indicate that it is number of practice trials rather than sessions that is important). What harm might arise if you provide a child with the government mandated 6 annual treatment sessions, targeting three patterns, but failing to achieve more than 100 practice trials for each target pattern across the 6 sessions? We can predict that the child will not start to generalize before the end of the block and therefore will not continue to make spontaneous gains after treatment stops. When the next block begins the child may be discouraged and less cooperative with the next SLP. The parent may become discouraged and seek out complementary or alternative interventions that are even more useless or harmful than speech therapy provided with insufficient intensity!

What if the child has achieved more than 500 practice trials and has not generalized? At this point you have more than enough reason to reassess your diagnosis and/or your approach. Child B in Weiner’s study for example did finally achieve many practice trials but did so slowly because he was unable to achieve the recommended intensity, producing much fewer than 80 practice trials per session. This child also failed to generalization after 500 trials for one of his targets. Perhaps this child was lacking in the necessary prerequisites such as stable perceptual and articulatory representations for the target phonemes. Or, perhaps the child viewed the communication breakdowns to be the SLP’s listening problem rather than his own speech problem and thus a disconnect at the level of the therapeutic alliance was hampering the child’s learning.  What about the children in Elbert et al who did not generalize at all? It was eventually revealed in the paper that these children presented with many “soft signs” indicative of both speech and oral motor apraxia. Therefore, continuing to almost 3000 practice trials for these children was most assuredly harmful, given that they were not benefiting from the approach and they were deprived of the opportunity to experience a treatment approach better suited to their needs.

I am hoping that this example in the specific context of minimal pairs intervention demonstrates that the concept of dosage can be very useful in speech therapy. We need much more research that establishes typical ranges of ‘dose’ for optimum outcomes for any given intervention procedure that we use. Then we need to track these dosages as we apply procedures in our interventions. It is important to remember that the dose is not the number of sessions or visits by the child or family to the SLP. Rather, the dose is number of learning opportunities experienced by the child. When the child is not learning and we know the child has experienced the optimum dose of practice trials, we can adjust our intervention procedures with greater confidence. We can also set evidence based goals for our clients and document objectively their progress with respect to these expectations. In addition to these benefits for individual clients, this kind of information will allow us to evaluate the efficacy of our service at the program level with an objectivity that is currently lacking. Imagine if a government or an insurance company suggested that they save money by reducing the dose of our medications below effective levels! We should not allow this solution to be proposed to reduce the cost of speech therapy services. The only way to protect ourselves and our clients is with more research and greater specificity about how our treatments work. We must know the right dosage.

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  1. Gabrielle Miller

     /  April 19, 2015

    This is a remarkable post! First, from studies written years ago (one 34 and the other 24), Dr. Rvachew has extrapolated data that informs current practice! Second, it is so helpful to have this data/information to use as a form of dynamic assessment of diagnosis and intervention – how children actually respond within a given framework of the number of practice trials and responses helps us to make more objective treatment choices. Thank you so much for this!

  2. Hi Susan, I am one of your former students in my first year of practice. I have been examining my own practice to strive towards being an effective as well as a good S-LP. I have two questions that have come up for me as I’ve tried to implement the information in this article. I know you are very busy, but I would love to hear thoughts from you or any of the readers of your blog.

    1. I usually try to practice phonological targets in a meaningful language activity. For example, to practice k initial words, I often let the child have a teapot of water and have them fill up a number of cups, each time asking for the cup. I think this is important for generalization. However, I have not yet been able to achieve 80-100 productions in 20 minutes with activities like this. I worry that perhaps I choose these activities because they are more fun then flash cards, and thus I am prioritizing being fun over being effective. Are trials in meaningful contexts an equal dose as out-of-context trials?

    2. Do you have evidence for what an effective dose is for input-oriented therapy?

    Thank you again for your blog – I have been glued to it and your textbook as I navigate my first year as an S-LP.

    • KHello Emily,

      It is great to hear from you. I am honored that you are following the blog and pleased that are using the book in your practice.

      Regarding your question about functional goals and activities in therapy, I have always thought that it was best to practice in functional contexts but I have been questioning that on the basis of animal research on feedback control as described in an earlier post (see On Birds and Speech Therapy). It may be that the children access feedback information best during drill practice, rather than during meaningful play activities so it is possible that it may be better to leave the more functional activities to the later stages of therapy. But this is not proven so in our research we are still using drill play but with an emphasis on the drill.

      We increase the trials by getting the child to produce more for every action. So with your example we would have five stuffed animals lined up and you would have five cups. The child must say cup five times for each cup. You adjust the level of support after each fifth trial, for example, direct imitation with direct feedback for the first cup, direct imitation with summative feedback for the second cup, delayed imitation with summative feedback for the second cup, spontaneous with direct feedback for the third cup, spontaneous with summative feedback for the fourth cup, spontaneous phrase (big cup) with direct feedback for the last cup. Now each animal has a cup, the child gets the teapot, you write your notes (I am pretending here that the child is at challenge point here all along, about 4/5 correct all along so you can keep moving up for each cup). Perhaps each animal would like a cookie, a cake and a candy to go with their cup. In no time you will have 100 trials and it is still meaningful. You need five minutes on either side to introduce the activity and to review homework with the mum and that makes a half hour session. We actually run 45 minute session because we have a prepractice period where we go really slowly and use all the techniques in our toolkit to make sure that the child can say the words or phrases that are required for the activity (ear training, phonetic placement, visual cues for each sound etc). Then the 20 minute practice portion is very intense.

      It is harder if the child has behavior problems. As you say the input oriented approach is an option when the child will not cooperate with this intensity or has problems specifically with phonological processing (phonological memory issues require a hybrid approach). We believe that intensity of input is important but in fact I do not have evidence for that. I did not have the resources to code the video from the ECRIP trial find out. However there is some evidence that kids with SLI for example will learns words with increased number of exposures-there is excellent controlled research on that.

      Speaking of the ECRIP trial, the final report has just been accepted for publication in AJSLP so there will soon be a published report showing that the input oriented approach can be as effective as standard articulation therapy.

      Thank you for your comment.


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