7.1 Introduction
7.1.1.4 Language acquisition and performance factors
Children’s behavior with language is also affected by numerous
“performance factors”, e.g., theirmemoryand ability to deal withlengthof lin- guistic utterances. The relation between these factors and linguistic knowledge is complex.
Children’s ability to remember what they hear is to some degree determined by their ability to structure it. Given a random list of terms like (5a), memory is likely to be deficient when compared to memory for the same list structured, e.g., (5b) (Epstein 1961).
5. a. brillig slithy toves gyre gimble wabe b. ’twas brillig, and the slithy toves
did gyre and gimble in the wabe. (Lewis Carroll, 15, TLG)
Earlier research has shown that memory and cognition are not independent in the child. Piaget and Inhelder argued that “the most important factor in the
4Huttenlocher and Weiner 1971; Huttenlocher, Eisenberg and Strauss 1968; Huttenlocher and Strauss 1968; Bloom 1974, 307.
5Relatively few studies of language acquisition have investigated precise interactions between developing linguistic and pragmatic knowledge in order to account for child language behaviors and to determine what aspects of children’s knowledge may be developing. See Blume 2002;
Kaufman 1994; Grimshaw and Rosen 1990; Boser 1995; Austin et al. 1998; Foster-Cohen 1990;
Clark and Grossman 1998; Crain and Thornton 1998; Drozd 2004.
126 c h i l d l a n g ua g e
development of memory . . . is its gradual organization” (Piaget and Inhelder 1969, 80, 1973).6
Recent research suggests that “infants’ memory processing does not fundamen- tally differ from that of older children and adults” (Rovee-Collier 1999, 80; 1997;
Rovee-Collier, Hartshorn and DiRubbo, in press; Rovee-Collier and Gerhard- stein 1997c, 32–33). Numerous experiments have evidenced infants’ remarkable capacity for memory of language stimuli (e.g., Jusczyk 1997, 124–125). At two months, they have been shown to remember a set of three different syllables, enough to detect a change in a single phonetic feature after a two minute delay, e.g., [si][ba][tu] when [ba] was changed to [da] (Jusczyk 1997, 125). At eight months, they recognized words from a story read to them two weeks earlier (Hohne, Jusczyk and Redanz 1994; Jusczyk and Hohne 1997). While infants’
memory surely affects their linguistic behaviors, it is also to some degree deter- mined by their linguistic knowledge.7
Children’s ability to deal with long utterances may also relate to their ability to structure these. Early speech is characterized by auniversal length constraint (e.g., Brown 1973c) which is gradually overcome, as in the progression from (6a) to (6d) (Bloom 1970a).
6. a. go# (G, age 19.1, MLU 1.12, Bloom 1970, 11) car#ride
b. Mommy jacket (G, age 20.2, MLU 1.34, Bloom 1970a, 93) Lois baby record
c. no open the wallet (G, age 23.3, MLU 1.79, Bloom 1970a, 184) d. no man ride this tank car (G, age 25.2, MLU 2.30, Bloom 1970a, 161) One young child’s multisyllabic vocabulary was largely produced as one syllable until the age of eighteen months, e.g., [po] for “piano” and [kiz] for “candies”
(Johnson, Lewis and Hogan 1997). In Finnish, where the proportion of multisyl- labic words is higher, children at early stages appear not to produce longer than disyllabic forms, e.g., [api] for “apina” (monkey) (Kunnari 2002, 128).
Length constraint on early language has led to a general developmental measure termed Mean Length of Utterance (MLU; after Brown 1973c and Cazden 1968).
This descriptive measure of early speech counts the number of morphemes in each utterance, sums over the utterances, and then divides by the number of utterances in the sample, as in (7).8
7. Computing MLU
dat bunny 2
dat bunny get juice on it 6 sloppy bunny 2
bunny hops 3
Total: 13/4 =3.25 MLU
6See Kail 1997 and Cowan 1997 for collected readings on the development of memory in childhood.
7Gathercole and Baddeley 1989 and Gathercole 1999 argue that phonological short-term memory in four- and five-year-olds may correlate with development of vocabulary.
8No precise definition of “morpheme” was provided.
MLU is widely used for describing general language development, especially up to MLU 3.5, when embedding, coordination and recursion are first observed (Brown 1973c).9 Different children overcome the length constraint at different rates. Figure 7.1 reveals normal variation in release of the length constraint in English acquisition among six children: the Harvard children, Adam, Eve and Sarah (Brown 1973c), and the children studied by Lois Bloom (1970a), Kathryn, Eric and Gia. Age and MLU do not correlate consistently and/or directly, especially within the first two years when MLU is often most quickly expanding.10
Although useful in a general sense for estimating general developmental lev- els of early language acquisition, MLU is a superficial measure which does not inform us directly of children’s grammatical knowledge. We still do not under- stand the source of the length constraint, how it is overcome, or how it interacts with grammatical knowledge.11Cross-linguistically, we still do not have a uni- versal typology of morphology, and the MLU measure is not comparable across languages (e.g., Hickey 1991, Dromi and Berman 1982).
Just as we cannot explain language development in terms of memory develop- ment, we cannot explain it in terms of length development. We must factor out the effects of a length constraint from developing grammatical knowledge.
Brown (1973c) suggested that development of a child’s MLU was an “excellent simple index of grammatical development because almost every new kind of knowledge increases length” (53). MLU does appear to be superior to age as a general descriptor for language development (e.g., Shipley, Smith and Gleitman 1969, 342; Lust 1977a).
However, the development of MLU does not correlate with grammatical
“stages” in the full sense of the term, e.g., (8) (cf. Brown 1973c, 58). It does not appear to precisely correlate with grammatical development.12
8. Basic properties of a “stage”
a. Distinct onset and offset time
b. General organization of the underlying grammatical system is distinct during that time
c. Widespread related unique characteristics characterize all structures during a distinct period of time
9 UB (Upper Bound) is another descriptive measure: the longest utterance in a child’s observed speech sample.
10Conant 1987; Klee and Fitzgerald 1985; Miller and Chapman 1981.
11Lois Bloom (1970) suggested that the length constraint “reflected an inability to carry the full structural load of the underlying representation. Limitations in linguistic operations appear to interact with limitations in cognitive function to influence linguistic expression in an as yet unspecified way” (169). It has been suggested that the length constraint on words may reflect
“. . . a limitation in the processing capacity required to retrieve and hold a lexical item, translate the auditory code to a sequential set of motor plans, and execute these plans” (Johnson, Lewis and Hogan 1997, 339, 347; see also Salidis and Johnson 1997).
12See Piaget 1983 and Gruber and Voneche 1977 on prerequisites for “stage” in cognitive development.
0.00
0.50
1.00
1.50
2.00
2.50
3.00
3.50
4.00
4.50 Age in months
MLU
Eve Adam Sarah Kathryn Eric Gia 161718192021222324252627282930313233343536373839404142
V IV III II I Fig.7.1VariationacrosschildreninMLUdevelopment
Grammatical competence
Grammaticality judgments Production Comprehension Fig. 7.2 Grammatical competence
In summary, assessing grammatical development requires dissociation of chil- dren’s linguistic competence from various factors involved in their performance with language, and application of the science of Linguistics in the context of the science of Psycholinguistics as well as Developmental Psychology. The researcher may do so through systematic application of a range of methods and measures.