Speech Perception and Persistent Speech Errors

Jon Preston is in my opinion the most interesting researcher to watch in the field of speech sound disorders. His recent studies on structural and functional brain differences in older children with persistent speech errors are very interesting. The two studies complement each other and point to structural and functional differences in supra superior temporal gyrus, consistent with repeated findings of perceptual deficits in children with speech deficits. Additional differences in supramarginal gyrus implicate integration of auditory and somatosensory information during feedback processes that are important for learning to produce speech sounds as well as monitoring and fine-tuning speech sound production as the articulatory system matures.

Given these neuroimaging findings, it makes sense to look for behavioral indices of perceptual difficulties in this population of children with persistent speech sound errors. Recently Preston et al (2015) used SAILS to do this with two different groups of school aged children. SAILS is a tool that I developed for speech therapy with preschoolers. Each module consists of natural speech recordings of adults and children producing a word that begins with a commonly misarticulated phoneme, for example, the word “rat”. Half the words are produced correctly and the remainder are misarticulated, e.g., [wæt], [jæt], [ɹ̮æt]. Each module is designed as a series of blocks in which the contrasts are theoretically closer, e.g., practice [ɹæt] versus [mæt], block 1 [ɹæt] versus [wæt], [jæt] and block 2 [ɹæt] versus [ɹ̮æt].  The child’s task is to identify the words that are “good” representatives of the target word. Although the blocks are numbered, they do not necessarily fall into a linear difficulty scale because each child can be quite idiosyncratic in terms of the features that they attend to. I’ll come back to this point later. After establishing that the tool was effective as an intervention for improving children’s speech perception and speech production skills, I found that it also had some value as an assessment tool (Rvachew & Grawburg, 2006) although I do not feel that the psychometric qualities are particularly good and I certainly did not design it for that purpose.

Now, back to Jon Preston’s study. In the first study, older children with [ɹ] distortions were compared to children with correctly produced [ɹ] and no history of speech delay. They were administered only the “most difficult” levels of SAILS modules including the [ɹ] Level 2 module. Although 1/20 children with typical speech and 6/27 misarticulators failed the [ɹ] SAILS module, the mean difference between groups was not significant. In the second study, a group of 25 children who received speech therapy as preschoolers was tested with SAILS, 3 years later when the speech deficit was resolved except in some cases for a persistent speech sound distortion. Performance on the “most difficult” [s] or [ɹ] module was correlated with their performance on an [s] or [ɹ] production probe. There was no correlation. (I was initially mystified by the perception results because they didn’t look like anything I had seen before but that was before I realized that the children were not presented with the complete test!).

So, how do we interpret these results? I have three comments.

First, Preston, Irwin, & Turcios have done us all a good turn by establishing that SAILS is NOT a good tool for assessing speech perception in 7 to 14 year old children with persistent speech errors. I never intended it for that purpose and I am pleased to have empirical evidence that supports a clear answer to the question when it comes up (we should be grateful to Seminars in Speech and Language for publishing it I suppose, despite the small samples, because rumour has it that ‘negative results’ are hard to publish). Anyway, we need something better for testing speech perception, especially for older children. I invite reader comments on what that “something better” would be. We know from many studies using synthetic speech that this population is at risk for perceptual deficits. We need to be able to identify those children in the clinic.

Second, if you are going to use SAILS for assessment (with children aged 4 to 7) it is very important to administer the complete module to the child, working through all the levels of the module, in order as intended. We cannot be sure that the child’s response to, for example Level 3 /s/, will mirror that of the normative samples who encountered Level 3 after first working through Practice, Level 1 and Level 2 before getting there. I will come back to this in another post in which I will give a sneak peek at the upcoming second edition of our book Developmental Phonological Disorders: Foundations of Clinical Practice.

Third, the relationship between speech perception and speech production is not linear. Even though I have found relationships between speech perception and speech production in the past using some rather fancy statistics with large groups (Rvachew & Grawburg, 2007; Rvachew, 2006), I cannot at the individual child level relate in a simple fashion SAILS score with number of correct productions of a phoneme. The reason is that the child’s production and perception of a phoneme is related to the way in which the child attends to the features associated with phoneme contrasts and certain features have different information value for perception versus production. We give an example of this in Chapter 4 of DPD (from Alyssa Ohberg’s masters thesis): preschoolers who were stimulable for /θ/ and /s/ but had not mastered this contrast were administered the SAILS /θ/ assessment module. Some children, in their speech, differentiated /s/-/θ/ by manipulating the duration cue whereas others differentiated /s/-/θ/ by manipulating the spectral cue; as you would expect, manipulating the spectral cue resulted in comparatively better articulatory accuracy but these two groups produced roughly comparable perceptual performance but with some interesting differences. The children who attended to the spectral cue actually did better on the supposedly “harder” level 3 stimuli than the supposedly “easier” level 2 stimuli, highlighting again that there is not a linear difficulty gradient across the stimulus blocks. The children who attended to the duration cue did surprisingly well at levels 2 and 3.  For some stimuli, attention to the duration cue actually provides an advantage. This results occurs because duration is actually a pretty reliable cue for perception of /θ/ but it does not provide any information that helps the child achieve the critical articulatory gestures (e.g., grooved versus nongrooved tongue,interdental versus alveolar tongue tip placement). In this case, there is no direct linear relationship between the child’s speech perception score and their speech production score on the tests that we gave. However, there is a direct relation between the child’s perceptual focus on only one of the relevant acoustic cues and their inability to produce the phoneme correctly. The only children who achieved good perception scores and good production scores attended to both the duration and the centroid cues.

This example raises a fourth point and that is, drawing on Shuster’s findings, the best test for older children may well involve using the child’s own speech production output. The most important question is, does the child mistakenly believe that their own productions are accurate and acceptable representations of the target category? I cannot recommend Shuster’s brilliant study highly enough for anyone treating this population. If the child does prove to have incomplete perceptual knowledge of /ɹ/ or /s/ however, treatment that includes highly variable (multi-talker) stimuli remains important, as a general rule of perceptual learning.

Further Reading

Preston, J. L., Felsenfeld, S., Frost, S. J., Mencl, W. E., Fulbright, R. K., Grigorenko, E. L., . . . Pugh, K. R. (2012). Functional Brain Activation Differences in School-Age Children With Speech Sound Errors: Speech and Print Processing. Journal of Speech, Language, and Hearing Research, 55(4), 1068-1082. doi: 10.1044/1092-4388(2011/11-0056)

Preston, J. L., Molfese, P. J., Mencl, W. E., Frost, S. J., Hoeft, F., Fulbright, R. K., … & Pugh, K. R. (2014). Structural brain differences in school-age children with residual speech sound errors. Brain and Language, 128(1), 25-33.

Preston, J. L., Irwin, J. R., & Turcios, J. (2015). Perception of Speech Sounds in School-Aged Children with Speech Sound Disorders. Seminars in Speech and Language, 36(04), 224-233. doi: 10.1055/s-0035-1562906

Rvachew, S. (2006). Longitudinal prediction of implicit phonological awareness skills. American Journal of Speech-Language Pathology, 15, 165-176.

Rvachew, S., & Grawburg, M. (2006). Correlates of phonological awareness in preschoolers with speech sound disorders. Journal of Speech, Language, and Hearing Research, 49, 74-87.

Shuster, L. I. (1998). The perception of correctly and incorrectly produced /r/. Journal of Speech, Language, and Hearing Research, 41, 941-950.

 

 

 

 

 

 

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