LANGUAGE PRODUCTION
2. SPEECH DELAY
2.1. From Functional Misarticulation to Optimality Theory: A Brief Tour Before terminology and perspectives from the discipline of psycholinguistics found
their way into thinking about speech sound development problems, children with a broad range of articulation problems but no obvious, underlying causal basis for the delay were called functional misarticulators (see McReynolds, 1988, for an outstanding analysis of the use of this diagnostic term; see also Barlow & Gierut, 1999). The delay was viewed
2There are many sources for typical speech sound development, which differ in certain details depending on sampling method, language, and so forth; excellent reviews of this work and references to the extensive older literature on developmental norms can be found in Grunwell (1981, 1987), Smit, Hand, Frelinger, Bernthal &
Bird (1990), Smit (1993), and Dodd (1995), among others.
3Again, there is a qualification to this claim that will not be pursued in detail in this chapter, but it should at least be mentioned that efforts to explain developmental speech sound errors on the basis of immature or faulty perceptual mechanisms have a long history in speech-language pathology (see McReynolds, 1988, pp. 422-424), but not one with much empirical success (see, for example, Locke, 1980a,b; Williams & McReynolds, 1975; Nittrouer, 1999). The psycholinguistic link is the possibility of immature perceptual mechanisms affect-ing a child’s ability to form proper category features for the contrastives sounds of her or his language. In fact, at least one theoretical strand in the literature on normal speech sound acquisition (Best, 1994; Kuhl, 1993) works from this perspective, so it is easy to see how it could be extended to children with speech sound pro-duction errors: they produce errors because they have a bad representation of the sound category as a result of deficient perceptual and/or categorization skills. As noted here, efforts to link specific production error types with specific perceptual problems have not been successful.
as functional in the sense of a poorly learned or willfully immature sound system, as opposed to neurological disease, hearing impairment, or structural abnormality (such as cleft palate) causing the errors. Functional misarticulation was clearly a wastebasket term (much like the use of the term idiopathic in the literature on certain diseases, as in Idiopathic Parkinson’s Disease), but it served the purpose of distinguishing speech-delayed children without obvious physical problems from those with a clear basis for their speech production problems. Most speech-language pathologists and scientists with interest in children labeled as functional misarticulators were uneasy, however, with the broadness of the label and its lack of prognostic guidance.
In particular, there was concern with variability in type and severity of symptoms of children diagnosed with functional misarticulation. Children with speech delay might present in the clinic with just a few errors, or many errors, and some of these errors may occur on some words but not others and at some times but not others for the same words (see below). In the early history of speech delay, there was a tendency for these errors to be regarded as separate entities; theoretical and practical links between the different kinds of errors and their conditions of occurrence were not recognized. Eventually there was recognition that developmental and clinical errors often grouped into sound classes (e.g., fricative errors), and as phonological theory advanced and accounted for more regulari-ties and systematiciregulari-ties in the sound structure of languages, so did the possibility of applying these notions to an explanation of speech sound errors. Moreover, as phonologi-cal theory and cognitive psychology began to see their reflections in each others’ gaze, psycholinguistics entered the realm of functional misarticulation where it has played a major role, in different ways, at least since the late 1960’s and early 1970’s. This history is nicely reviewed by Gierut and Morrisette (2005).
One of the primary interests in the literature on speech delay has been the relationship between an observed error and the form and/or processes underlying its production. With respect to underlying forms (or the ‘input units’ of optimality theory (OT): see below), most investigators and clinicians have assumed them to be no different from those in the normal, ambient phonology. Thus the child who says [tIti] for kitty or [kul] for school is generating her or his word productions from the representations /kIti/ and /skul/. This assumption is largely one of common sense, but also may have been thought to enjoy indirect empirical support from the lack of apparent perceptual problems – a near-normal ability to discriminate between phonemes – among children with speech delay (see foot-note 3, and discussion in Hewlett & Waters, 2004). In the typically developing infant such phoneme-discrimination abilities have been demonstrated for specific cases as early as one month of age and for a broad range of phonetic events before six months of age (see Houston, 2005, for a review), so the presence of an intact perceptual phonology in children with speech delay may lead to a very simple conclusion: the majority of sound errors pro-duced by children with speech delay are phonetic in nature, probably a result of articula-tory immaturity and therefore best described using phonetic, not phonological methods (see a form of this argument in Hewlett & Waters, 2004, and discussion of phonetic pressures on phonological description in Locke, 1983). However, claims including a lack of isomorphism between the perceptual and productive phonologies (Menn, 1980;
Straight, 1980) as well as the success of certain phonological analyses in accounting for regularities in groupings of sound errors, called this assumption into question.
Evidence of possible differences between the receptive and productive phonologies is typically drawn from examples of specific production errors that are rejected by the children themselves when an adult produces the aberrant form. Berko and Brown (1960) described a famous example of a child who produced [fis] for fish but labeled as erroroneous an adult’s production of [fis] for fish. A similar example, one with more direct relevance to the application of phonological process analysis to delayed speech, was reported by Weismer, Dinnsen, and Elbert (1981) who described three children who regularly omitted final stop consonants from words like dog and cab but who did not like adults’ productions of these words without the word-final stops; these children also pro-duced evidence of having the correct, underlying forms when asked to inflect the stems (e.g., children who said [do] for dog nevertheless produced [doi] when asked to give the name for a little dog).
Whatever the assumption concerning underlying forms, an observation made by many investigators was that speech sound errors often occurred in groups tied together by an underlying theme. The child who omitted the word-final // in dog, for example, was also likely to omit other, and perhaps most word-final obstruents. Similarly, the child who produced /kul/ for school most likely produced other s⫹ stop sequences (as in words like spot and stop) by reducing the cluster to a singleton consonant. This observation led to a reformulation of the ‘functional misarticulation’ notion, specifically by implicating phonological processes as a key player in normal speech sound development as well as in many cases of speech delay. A phonological process is a psycholinguistic operation applied to the underlying representation, the output of which is a surface form. When a child produces open-syllable forms for words with final consonants (e.g., [do] for dog, [k] for cat, [mi] for miss), a process of final consonant deletion is said to intervene between the (correct) underlying form and the surface representation. Interestingly, it is known that at various stages in the learning of the ambient phonology typically develop-ing children often omit word-final consonants, produce only one consonant instead of two or three in target clusters, and solve the apparent difficulty of fricatives by producing them as stop consonants. Whereas previous descriptions of speech sound development, and treatment plans in cases of speech delay, treated individual sound errors as more or less independent entities or paid attention to classes of speech sounds (such as fricatives), the phonological processes of final consonant deletion, cluster reduction, and stopping of fricatives, among others, were believed to capture the organized nature of developing and delayed sound systems in a way that transcended sound classes and reflected the cognitive reality of phonological structure. Phonological processes were therefore thought to provide a more elegant account of speech learning behavior.
Phonological processes, as reviewed by Ingram (1976), Locke (1983), Shriberg and Kwiatkowski (1980), and Elbert, Dinnsen, and Weismer (1984), signaled in at least two important ways a specific paradigm shift in the view of children with speech delay. First, the idea that psycholinguistic processes mediated between the underlying, phonological
forms and their phonetic realizations signaled a subtle shift away from the belief that speech motor maturity played a central role in the sequence of typical speech sound development, and in speech delay. True, many phonological processes in typical and delayed development resulted in presumptive articulatory simplifications as inferred from markedness conventions (see Hyman, 1975, Chapter 5 for an excellent review of markedness and its relation to articulatory simplification and ‘natural’ phonological processes). Thus consonant–vowel–consonant (CVC) syllables reduced to CV by a process of final consonant deletion was consistent with articulatory simplification be-cause CV is the umarked form. The same can be said of consonant singletons relative to clusters, and stop consonants relative to fricatives. The shift from speech motor maturity to phonological processes as explanations for speech sound errors is in some ways a sub-tle move, in light of the strong influence of the markedness concept on the phonological processes noted frequently in typically developing phonologies and cases of speech delay. Clearly, investigators conceived of the shift as one from an articulatory-motor to linguistic perspective, but the linguistic apparatus seemed to be based on articulatory simplicity. If phonological processes are merely a new descriptive device whose motiva-tion is much the same as speech motor maturity, why submit to the paradigm shift?
The answer was in the second aspect of the paradigm shift. Phonological processes suggested a mechanism for the joint mastery of multiple sounds, often cutting across sound classes, in typical development or as a result of treatment in cases of speech delay.
In treatment from a speech motor maturity perspective, children would often be given articulatory drill as a form of speech motor practice for specific speech sounds; the repetition was assumed to automatize4the articulatory behavior required for correct pro-duction of the sound. Treatment from the perspective of phonological processes viewed the child’s production problem as one of rule-learning (or unlearning, as the case may be:
see Stampe, 1973), for which a properly constructed remediation plan would not only exploit at least some of the multiple sounds encompassed by the rule but also result in the normalization of all such sounds affected by the process. Thus the child who deleted word-final obstruents would be taught, by use of multiple but not exhaustive examples of syllable-closing consonants, the concept of closed syllables.
More recently, OT has been argued to supercede phonological processes as a putative account of speech sound learning in typical development, and to show great promise in explaining errors and their treatment in speech delay. Briefly, OT assumes a set of con-straints operating between underlying forms – termed inputs – and output forms which are the surface (phonetic) representations. The constraints, thought to be universal, mediate the relationship between input and output forms by virtue of their ranking, which
4 Automatized is a term from the older speech pathology literature (see, for example, Johnson, Shelton, Ruscello, & Arndt, 1979), signifying a process whereby a motor behavior becomes routinized or ‘burned in’ to neural circuitry by virtue of multiple repetitions. It obviously shares much with notions of motor skill acquisi-tion in sports and musical performance. The term still shows up in the professional literature on reading and even speech perception (Johnson & Ralston, 1994).
is highly flexible. Operating under a basic goal of obtaining the same number of seg-ments in the input and output representations (the faithfulness constraints), the best match is sought between input and output forms but not at the expense of violating highly ranked constraints which dominate lower-ranked constraints in a sort of tournament model. A very good introduction to OT and its application to sound development and delay is found in Barlow and Gierut (1999).
OT has been claimed to be a better paradigm than phonological processes for under-standing developmental speech sound errors – typical or delayed – because processes are seen as relatively clumsy in their sequential application (as compared to the parallel pro-cessing in OT) and are ill-adapted to handling the common intra- and inter-child variability in speech sound production (see below). Markedness, however, is a prominent concept in both paradigms. Early in typical development, and presumably for children with speech delay, markedness constraints in OT are ranked very high and therefore result in mis-matches between input and output forms. For example, syllable shape has been proposed as a highly ranked markedness constraint in the early stages of typical speech sound de-velopment (Barlow & Gierut, 1999). By virtue of this high ranking, input syllables having CVC form will be realized in the output as CVs because the syllable shape markedness constraint dominates lower-ranked and more easily violated faithfulness constraints of matching the number of input and output segments. Similarly, markedness constraints of
‘no consonant clusters’ and ‘no fricatives’ rank very highly in early phonological devel-opment and therefore result in cluster reduction and stopping of fricatives, respectively.
Gradually, with the progression of typical development or as a result of speech therapy, markedness constraints lose their high ranking – in the language of OT, they are demoted – and better matches are obtained between input and output forms. Importantly, the constraints do not disappear, like certain phonological processes that are undone as devel-opment proceeds, but they are reorganized. The constraints can be thought of as a variably programmed filter, the soft assembly of which resides in their flexible ranking. At differ-ent times throughout developmdiffer-ent, this filter will transform the input in differdiffer-ent ways until the proper filter configuration – yielding the adult output – is achieved.
Why would a universal set of constraints get reranked over the course of normal development or speech therapy? It appears this question has not yet been treated in the kind of theoretical depth required for OT to emerge as a truly compelling account of speech sound errors. Some clues as to how this aspect of OT will be developed have been summarized by Boersma and Levelt (2003), who argue that reranking of constraints is driven by production errors and their comparison by the learner to the ambient phonol-ogy – that is, the targets used by adults. Presumably, the learner develops over time some sort of quantitative model of mismatches between her output and adult forms, the cumu-lative effect of which is a reranking of constraints to better match her output to the adult forms. This notion carries with it the assumption for the child learner of adult-like, pho-netic perceptual skills, as well as the related OT assumption of adult-like underlying forms. If these assumptions are not operative , of course, the markedness filter of the early constraint rankings (what Boersma & Levelt refer to as the ‘emergence of the unmarked’) makes little sense.
These considerations again raise the question, posed earlier, for both OT and phono-logical processes as they apply to typical speech sound development and speech delay: If both depend so much for their explanatory substance on markedness, a concept with much allegiance to articulatory complexity (and by inference speech motor maturity), what advantage is gained by the reformulation of speech sound development and delay in psycholinguistic terms? Considering phonological processes first, even if they are mo-tivated partially or largely in the same way as speech motor maturity, the potential for rule induction moves past the presumptive neural nuts and bolts of articulatory practice, either as a part of typical development or as a remediation strategy (see above). Similarly, OT would view speech sound errors as the result of a constraint ranking that differs from the ranking adhered to by speakers with ‘normal’ phonologies. Barlow & Gierut (1999, p. 1491) clearly summarize these issues for the case of typical development.
Extending this to phonological acquisition, these constraints that are present at initial stages of development are also assumed to be the very same constraints present at later points in time. The longitudinal course of developmental change is character-ized by reranking constraints. The likelihood is that the markedness constraints in particular will be demoted in children’s systems. This follows from the observation that markedness constraints outrank faithfulness constraints in development, which is just the reverse pattern in fully developed systems…. Notice that this view of change is different from prior derivational accounts involving phonological processes or rules that are lost, suppressed, or eliminated from the grammar over time.
2.2. Consistency and Modifiability of Errors: Does the Theoretical Viewpoint