Feature analysis of segmental errors in children with phonological disorders.

There has been a longstanding controversy about the existence, nature, and differentiation of developmental apraxia of speech (DAS), leading to numerous investigations of characteristics that define this articulatory disorder. An analysis of substitutions relative to target sounds led Thoonen, Maassen, Gabreëls, and Schreuder (1994) to conclude that children with DAS show a pattern of feature retention in their error productions that contrasted with that of children with normal articulation. This pattern, in which place of articulation was retained in the substituted sound less frequently than manner of production or voicing, was considered by Thoonen et al. to be of diagnostic significance. The current research re-examines this claim by comparing the retention patterns obtained by Thoonen et al. for children suspected of having DAS to patterns for children suspected of having a phonological disorder. An examination of substitutions used by 20 children who were diagnosed with and treated for phonological disorders demonstrated the same pattern of feature retention that was described for children with DAS. The results of this study showed that voicing is maintained most frequently; manner of production is the next most retained feature; and place of articulation is the feature that is retained least often when a substitute is used for a sound that isn't produced correctly. In a second analysis, this pattern of feature retention was compared to children's phonological knowledge as indexed by percent correct underlying representation (PCUR). Contrary to the findings of Thoonen et al., however, the present work found an inverse relationship between retention of place and phonological knowledge. Children with greater phonological knowledge retained place less often than children with more limited phonetic inventories. These patterns of feature retention may be representative of specific development sequences that occur during phonological acquisition.

Lexical constraints in phonological acquisition.

Lexical diffusion, as characterized by interword variation in production, was examined in phonological acquisition. The lexical variables of word frequency and neighbourhood density were hypothesized to facilitate sound change to varying degrees. Twelve children with functional phonological delays, aged 3;0 to 7;4, participated in an alternating treatments experiment to promote sound change. Independent variables were crossed to yield all logically possible combinations of high/low frequency and high/low density in treatment; the dependent measure was generalization accuracy in production. Results indicated word frequency was most facilitative in sound change, whereas, dense neighbourhood structure was least facilitative. The salience of frequency and avoidance of high density are discussed relative to the type of phonological change being induced in children's grammars, either phonetic or phonemic, and to the nature of children's representations. Results are further interpreted with reference to interactive models of language processing and optimality theoretic accounts of linguistic structure.

Lexical characteristics of sound change.

The purpose of this study was to determine the relationship between sound change and lexical structure in two children with functional phonological disorders. Specifically, the question of how sound change infuses through the developing lexicon was addressed. A chronology of phonemic acquisition for the children who participated has previously been documented. These archival data were now extended to evaluate lexical change relative to sounds acquired. Lexical change was examined through the parameters of neighbourhood density and word frequency. Results of this study revealed two converging patterns across children: (a) for each child there was one parameter (neighbourhood density or word frequency) of lexical change which held across all sounds acquired, and (b) for each child the alternative parameter patterned differentially by sound. This variability in lexical change was hypothesized to be associated with the relative degree of feature specification of the sounds acquired. This has theoretical implications for the overlay of phonological and lexical structure, and clinical potential for remediation of phonological disorders.

Triggering a principle of phonemic acquisition.

This experimental clinical study evaluated different treatment manipulations of the principle of Laryngeal-Supralaryngeal Cyclicity as a follow-up to Gierut (1994b). Laryngeal-Supralaryngeal Cyclicity states that the acquisition of phonemic distinctions will occur as a bivalent cycle with laryngeal and supralaryngeal distinctions emerging in turn. In this study, children with seemingly static phonemic systems participated in a treatment programme that introduced sequentially new distinctions to the inventory. One child was presented with alternating laryngeal and supralaryngeal properties consistent with the principle, whereas the other child was exposed only to consecutive supralaryngeal distinctions. Results indicated that the latter treatment condition triggered greater phonemic expansion, as based on the longitudinal course of emergent phonemic distinctions for each child. These findings were comparable to those of the earlier investigation, and have implications for treatment efficacy and theories of language acquisition.