LANGUAGE PRODUCTION
2. SPEECH DELAY
2.2. Consistency and Modifiability of Errors: Does the Theoretical Viewpoint Matter?
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
suggest a therapeutic focus on the highest-ranking constraint indicated by the child’s sound error pattern, the assumption being that its demotion will, by implication, ‘pull along’ lower-ranked constraints to lower levels thus eliminating the mismatches between input and output forms that suggested speech delay and prompted treatment.
It would seem as if a good test of these different phonological theories would be found in the results of different forms of treatment and the diagnostic procedures from which they are derived. Unfortunately, as in most kinds of human behavior, it is not quite so simple. First, most kinds of therapy for children with speech delay produce positive effects (Gierut, 1998), making it difficult to choose between theories underlying different treatment strategies. The most desirable kinds of experiment to address competing theo-ries would be to organize a group of children of the same age and with the same profile of phonological delay, with random assignment of each child to one of the treatments based on different theories. The ability to conduct such an experiment is obviously very limited, for the obvious and many logistical reasons known to investigators who do treat-ment research. More basically, this experitreat-ment presupposes clear-cut predictions between the different theories. OT, for example, makes certain predictions concerning which constraints should produce the greatest effect throughout a delayed phonology, but it seems as if the same kind of predictions might be made (at least in certain cases) by a phonological process approach. This makes sense because both theories are, as discussed above, dominated by markedness considerations.
With these caveats in mind, here is what seems to be known about the relationship between theory and treatment planning. There is a general sense, perhaps counterintuitive at first blush, that treatment with the greatest potential for generalization should always focus on sounds having some form of greater, as compared to lesser complexity within an ambient sound system. For example, experimental evidence reviewed in Gierut (1998) and Gierut and Morissette (2005) suggests greater generalization with treatment of more, as compared to less phonetically complex sounds (e.g., fricatives vs. stops), later as compared to earlier developing sounds (e.g., certain glides vs. stops), and non-stimulable as compared to stimulable sounds. This latter finding requires some additional comment. When a child presents in the clinic with multiple sound errors, the clinician wants to determine which of these error sounds can be produced correctly by the child under optimal diagnostic condi-tions, and then increasingly more complex conditions. ‘Optimal diagnostic conditions’
implies sound production with minimal influences of phonetic context and lexical identity, as well as of pressures to formulate language and convey an intelligible message. When a child can produce one of her error sounds correctly, under optimal conditions, the sound is said to be ‘stimulable’; the child is said to be ‘non-stimulable’ for those sounds remaining in error even under the best of production conditions.5 It is worth repeating the finding
5The precise notion of stimulability is not codified in the speech-language pathology literature, and is best thought of as a relative notion. For example, some children may be identified as stimulable for sounds in isolation, others for sounds in isolated words; or, the notion of stimulability may depend on how a correct production is elicited (auditory stimulus, placement of articulators by the clinician, and so forth). See Bauman-Waengler (2000, pp. 132–133) for a review of stimulability and clinical diagnosis.
reported by Gierut (1998): when a child has multiple sound errors, treatment of the non-stimulable sounds seems to generate more widespread change throughout the sound system as compared to treatment of stimulable sounds. The overall message seems to be, the more complex the work, the more generalization will occur.
This provisional notion of greatest generalization being achieved when treatment
‘targets’ are chosen from the high end of the phonetic complexity continuum may have a unifying expression in the hierarchical constraint structure of OT. Recall that one view of normal phonological development entails a reranking over time of a fixed set of constraints, with the typical progression of markedness constraints dominating faith-fulness constraints early in development, but gradually demoted below faithfaith-fulness constraints to allow the emergence of adult forms. It has been hypothesized that within the set of markedness constraints, certain fixed rank orders may not be violated, even when one constraint within a set is demoted. This important aspect of the potential explanatory power of OT is worth a fairly detailed consideration, using an example from the literature.
Dinnsen and O’Connor (2001a) have presented a theoretical analysis of two common errors in typical phonological development, consonant harmony and gliding. The former error can be characterized as “… an assimilatory process that copies or spreads place or manner features to either a consonant or glide elsewhere in the word” (Dinnsen &
O’Connor, 2001a, p. 599). An example of this error is the target word won (/wn/) produced as none ([nn]). The latter error, gliding, involves a change in consonantal /r/
or /l/ to [w], as in error won ([wn]) for target run (/rn/). Dinnsen and O’Connor (2001a) note the co-occurrence of these errors in the developing phonologies of several children and ask the logical question, why should these errors be seen together (see also Dinnsen & O’Connor, 2001b; Gierut & Morissette, 2005, for additional examples of co-occurring error types)? A derivational approach to phonological errors – for example, explanations of the errors involving phonological processes – cannot provide a reason for these kinds of co-occurrence and in fact treats them as chance (or at least unprincipled, with respect to theory) pairings. Dinnsen and O’Connor (2001a) show for several children and by appeal to a data base of phonological errors, however, that not only do consonant harmony and gliding co-occur but they do so with a unidirectional, implica-tional relationship. Specifically, if consonant harmony errors are present gliding errors will be as well (i.e., errors of consonant harmony imply errors of gliding), but gliding errors can exist alone and hence do not imply consonant harmony errors. If derivational accounts cannot provide principled accounts for the co-occurrence of errors, they certainly cannot explain a one-way, implicational pattern such as the one just described.
The advantage of OT in understanding phonological development and disorders is best exemplified in the way the theoretical apparatus can explain error co-occurrences and their implicational relations. This explanation, in turn, points to a principled selection of treat-ment targets having the greatest potential for generalization to untreated sounds. In the current example, Dinnsen and O’Connor (2001a) argue for a universal constraint ranking in which the constraint for avoidance of [r] always outranks the constraint for matching
the place or manner features of consonants within a word.6Thus if the latter constraint filters the input (the underlying representation), so must the former because all higher-ranked constraints must apply; but the highest-higher-ranked constraint in this example – avoid [r] – can filter the input and result in gliding without requiring the presence of consonant harmony, which is produced by a lower-ranking constraint. The implicational, one-way relation is captured by the constraint ranking. Clinically, the logic of OT holds that in a child with consonant harmony and gliding errors, a treatment focus that targets and successfully demotes the ‘avoid [r]’ constraint will pull along the ‘consonant harmony’
constraint as well, because of their fixed and universal ranking. On the other hand, target-ing the harmony constraint, even if successful, will only change those errors, leavtarget-ing the higher ranked constraint to filter the input as before and thus produce gliding errors. If this concept is correct, the most efficient and productive use of a clinician’s time in treating a child with these co-occurring error patterns would clearly be to focus on gliding.
Gierut and Morrisette (2005) describe some clinical data for a different pair of co-occurring errors, consistent with the concept of fixed constraint ranking and implicational relations. Stopping (the substitution of stops for fricatives, as in [tn] for sun (/sn/), very common in typical, developing phonologies and in children with speech delay) and liquid gliding are said to co-occur as a result of the following, fixed constraint ranking:
‘avoid liquids’ must outrank ‘avoid fricatives’. This ranking requires gliding to co-occur when stopping is present, but allows gliding to exist when fricatives are produced cor-rectly (or at least without stopping; there are other kinds of fricative error, discussion of which is beyond the scope of this chapter). Gierut and Morrisette (2005) cite treatment results of Tyler and Figurski (1994), who identified two children with this pair of errors and showed that the child treated for demotion of ‘avoid fricatives’ did not show generalization to liquids, but the child treated for demotion of ‘avoid liquids’ showed generalization to fricatives. Once again, a treatment effect wherein elimination of one member of a pair of co-occurring error patterns generalizes to the other member, but only in one direction; the effect seems to be ‘explained’ by the constraint rankings of OT and the implicational error patterns implied by them.
Can these treatment effects be viewed through the lens of complexity, as discussed above? The hypothesized, fixed universal constraint rankings, using the non-technical language adopted here for the two examples of co-occurring errors, are shown below.
Error pairs → [w] for /r/ & consonant harmony [w] for /r/ & stopping
Constraints → Avoid [r] Avoid [r]
Match consonant manner Avoid fricatives
6The jargon and assumptions of optimality theory are being simplified for this discussion. OT would call the first constraint ‘*R’ ( ‘avoid [r]’ (actually, avoid the co-occurrence of [⫹ consonantal] and [approximant]), and the second constraint ALIGN (manner features must be aligned with the left edge of prosodic domain).
These are all markedness constraints, by definition having the function of simplifying the output relative to the input (underlying forms). For any one of the constraints, there is probably little argument about their simplifying nature, but a more pertinent question is why one markedness constraint gains supremacy over another, a necessary condition to produce the one-way, implicational error patterns and preferred clinical targets dis-cussed above. Is the production of /r/ more obviously complex than the production of two different manners of consonant articulation with the same word or the production of fricatives? Or, are the kinds of universal, fixed constraint rankings invoked by Dinnsen and O’Connor (2001a, 2001b) and Gierut and Morrisette (2005) more reasonably de-scribed as descriptions of error patterns elevated to the status of theory, and made to fit the particulars of the theory? What is needed to move OT forward with respect to speech sound development and delay is an extensive data base and analysis of co-occurring error patterns, as well as additional theoretical development of rankings within the set of markedness constraints.