I’m following up on my review of Kiparsky and Menn (1977) with a review of Hewlett (1990), which extends the dual-lexicon model in several interesting ways, including a more detailed production component and an updated literature review. Unfortunately, the chapter is so long that it doesn’t really seem appropriate to review it all at once. In fact, this post will probably be too long. If you’d prefer shorter posts, let me know!
Hewlett reviews major findings in normal and disordered phonological/speech development, with the goal of motivating a model of early speech production building on previous work [1, 2]. The coverage in the manuscript is extensive, and the criticism is often very insightful. Below is a short description of the findings that Hewlett covers.
Hewlett begins his review with very early speech development, including babbling.* Babbled sounds are typically the same sounds in early words, and babbling usually overlaps with the first real word productions . Relevant work not discussed by Hewlett include research from Boysson-Bardies and colleagues showing that babbling sounds are language dependent and even sounds that are common in babbling around the world often have language-specific phonetic characteristics [4, 5].
When word production begins in earnest, Hewlett argues that certain aspects of early speech are consistent. First, early ‘proto-words’  are highly variable in their form. Thus, although the child’s production goal might be consistent—for example, they are always referring to ‘milk’—the form is entirely inconsistent. Second, early words are generally single words or unanalyzed phrases (the parts of the phrase don’t recombine).
Hewlett argues that a separate stage can be identified around 1;6 (years; months), which roughly corresponds to what is often called the ‘word spurt’. Hewlett further elaborates on phonological systematicity during early word production. Young children apply systematic patterns to their speech. These patterns might include consonant cluster reduction (‘snow’ is pronounced [no]), or application of a child-language-specific rewrite rule (/r/ à [w] word-initially and word-medially), or application of a prosodic template, such as a [CVjVC] template . Hewlett writes, “The important implication of this is that the child’s pronunciation patterns exhibit regularities which yield to a systematic description within a phonological framework.” (p. 19) Thus, the enterprise of child phonology has been either to 1) describe the child’s phonological inventory, including contrasts and phonotactic restrictions, or 2) write rules that describe how children get from the adult form, which children are presumed to know based on their perceptual abilities. I will not go into great detail about these proposals, but Hewlett reviews well-known rules such as /r/ à [w]. Finally, although Hewlett discusses the issue later in the paper, this stage of phonological development includes many examples of ‘lexical avoidance’, or cases in which children avoid words with particular sounds .
At this point, Hewlett reviews models of phonological development, including proposals by Jakobson , Stampe , and Menn (; the dual-lexicon model, also described in , which I reviewed in a previous posting). He then goes on to describe children’s perceptual abilities, which are generally agreed on to be quite good. And, of course, the explosion of the infant literature starting in the early 1990s confirms that infants are very good at learning linguistic/phonological patterns before they begin to speak.
As a sort of contrasting section to `phonological development’ as described above, Hewlett reviews `phonetic development’, in which he focuses on the measurement of speech production. Several findings are noteworthy. First, children’s speech is known to be more variable, including long durations for linguistic targets and greater variability. Regarding variability, recent work by my current mentor Lisa Goffman, and her collaborations with her mentor Anne Smith, have greatly added to our understanding of speech motor variability in children. Some examples:  showed that oral-motor stability is below adult levels even at 14 years of age.  showed that, contrary to what one might expect from a frequency-based explanation, native English speaking children and adults produce iambs with more stability compared to trochees.
Continuing with Hewlett’s discussion of phonetic development, children’s formants tend to be more variable than adult’s formants . Hewlett discusses the issue of whether children show more or less coarticuation than adults. A number of researchers, Susan Nittrouer being one example , have claimed that children actually show greater amounts of coarticulation. The implication is that children have less segmentalized speech, and therefore their early speech consists of unanalyzed whole words. This claim has been hotly debated (or was hotly debated 20 years ago), but it appears that coarticulation is often just different in children , without there being either more or less coarticulation in child speech.
Hewlett also discusses the issue of `covert contrasts’ or `incomplete neutralization’—cases where children appear to be producing two sounds the same but are actually producing them distinctly. For example, both /r/ and /w/ might be realized as something like a [w], but in fact, the productions are distinct, and children can reliably identify which word they intended from their own productions . Elsewhere, I have argued that this is a systemic problem with analyses of child phonology. Because so much of the literature on `phonological processes’ in child speech is based on transcription data, it is unclear whether these cases reflect phonological processes or covert contrasts (in which case, `phonological’ must mean something entirely different than what it is usually taken to mean).
Hewlett concludes his review of phonetic development with three findings. First, sounds that appear in babbling may disappear from a child’s sound inventory after the onset of word production. Second, although adults are very good at compensating for a bite block and hitting acoustic targets, children may be less good at this . Third, Hewlett notes that children seem readily able to acquire a foreign accent as well as a foreign language (although some more recent work  suggests that accent acquisition generally falls on a continuum based on age of acquisition). Regarding the last two findings, Hewlett concludes that children must be better than adults at learning to produce new sounds.
 Kiparsky, P. & Menn, L. (1977). On the acquisition of phonology. In Language Learning and Thought, J. Macnamara (Ed.). New York: Academic Press.
 Menn, L. (1983). Development of articulatory, phonetic, and phonological capabilities In Language Production, Vol II, B Butterworth (Ed.). London: Academic Press
 Locke, J. L. (1983). Phonological Acquisition and Change. New York: Academic Press.
 Boysson-Bardies, B. d., Halle, P., Sagart, L., & Durand, C. (1989). A crosslinguistic investigation of vowel formants in babbling. Journal of Child Language, 16(1), 1-17.
 Boysson-Bardies, B. d., & Vihman, M. M. (1991). Adaptation to language: Evidence from babbling and first words in four languages. Language, 67(2), 297-319.
 Menyuk P. & Menn, L. (1979). Early strategies for the perception and production of words and sounds. In Language Acquisition, P. Fletcher, M. Garman (Eds.). Cambridge, UK: Cambridge University Press. pp. 49-70.
 Priestly, T. M. S. (1977). One idiosyncratic strategy in the acquisition of phonology. Journal of Child Language, 4, 45-66.
 Schwartz, R. G., & Leonard, L. B. (1982). Do children pick and choose? An examination of phonological selection and avoidance in early lexical acquisition. Journal of Child Language, 9, 319-336.
 Jakobson, R. (1968). Child Language, Aphasia and Phonological Universals. The Hague: Mouton.
 Stampe, D. (1969). The acquisition of phonetic representation. Papers from the 5th Rebional Meeting of the Chicago Linguistic Society, 443-454.
 Smith, A. & Zelaznik, H. (2004) Development of functional synergies for speech motor coordination in childhood and adolescence. Developmental Psychobiology, 45, 22-33.
 Goffman, L. (1999). Prosodic influences on speech production in children with specific language impairment and speech deficits: Kinematic, transcription, and acoustic evidence. Journal of Speech, Language, and Hearing Research, 42, 1499-1517.
 Eguchi, S. & Hirsch, I. (1969). Development of speech sounds in children. Acta Otolaryngology Supplement, 257.
 Nittrouer, S., Studdert-Kennedy, M., & McGowan, R. S. (1989). The emergence of phonetic segments: Evidence from the spectral structure of fricative-vowel syllables spoken by children and adults. Journal of Speech and Hearing Research, 32, 120-132.
 Goodell, E. W. & Studdert-Kennedy, M. (1993). Acoustic evidence for the development of gestural coordination in the speech of 2-year-olds: A longitudinal study. Journal of Speech and Hearing Research, 36, 707-727.
 Kornfeld, J. R., & Goehl. (1974). A new twist to an old observation: Kids know more than they say. Chicago, IL: Chicago Linguistic Society.
 Oller, D. K. & MacNeilage, P. F. (1983). Development of speech production: Perspectives from natural and perturbed speech. In The Production of Speeech, P. F. MacNeilage (Ed.). New York: Springer Verlag, pp. 91-108.
 Flege, J. E., Munro, M. J. & MacKay, I. (1995). Factors affecting degree of perceived foreign accent in a second language, Journal of the Acoustical Society of America, 97, 3125-3134.