Tager-Flusberg & Zukowski (2009) 147-173

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Text of Tager-Flusberg & Zukowski (2009) 147-173

  • Measuring Syntoctic Growth 147

    [NrrnrNG THE coMpLEX LrNGUtsTtc sysTEMOne of the most difficult issues about acquiring language that the child faces is howto break into the system. How do children manage to break up the steady stream ofsounds they hear into basic units like words and morphemes? How do they learn tomap specific sound sequences onto meanings? And how do they learn to figure out thebasic grammatical categories of their language, such as nouns, verbs, and adjectives?These are some of the fundamental questions about language acquisition that childlanguage researchers must also address in their theories, even though young childrenat the earliest stages of development provide us with few clues'

    One interesting hypothesis that has received some empirical support has beensuggested by Morgan (1986), among others. According to Morgan, if adults providedinformation in their speech to children about where boundaries exist, not only betweenwords but also between phrases, the task of acquiring language would become feasibleand simplified.

    There does appear to be evidence that mothers and fathers provide strong into-national or prosodic evidence about word and phrase boundaries, not only in English,but also in other languages, such as French and Japanese (Fernald et al., 1989). Moreimportant, there is also evidence that infants are sensitive to the salience of the infor-mation sent in pauses (Jusczyk, 1997; Shi, \7erker, 6c Morgan, 1999).Shady andGerken (1999) found that very young English-speaking children are sensitive toprosodic cues as well as other cues provided by their caregivers in experiments thattested their abiliry to understand spoken language. Extending this research to childrenlearning other languages, Shi, Morgan, and Allopena (1998) found that caregivers'speech to infants acquiring both Turkish and Mandarin Chinese contained similarkinds of phonological and acoustic cues that allowed them to distinguish different lex-ical and grammatical categories.

    Once the child has broken the stream of speech into words, he or she may useother "bootstraps" into the syntactic system. Some researchers have suggested thatmeaning, or semantics, plays a key bootstrapping role for the child (e.g., Pinker, 1984);others suggest that the functions of language , or Pragmaticg provide the primary routeinto the abstract grammatical system (e.g., Tomasello,2002).A third alternative is thatgrammar provides its own bootstrapping operadon, suggesting that it operates as an in-dependent cognitive sysrem. W'e will consider the role that semantics, pragmatics, andgrammar play in facilitating grammatical development at each of the different stages ofthe process.

    ffi rasunrNc sYNTACTIc GRowTHfu children grow older, their sentences get longer. Studies of large numbers of childrenhave provided excellent normative data on the age at which English*peaking childrenmake the transition to combining words and using simple sentences. These data come

  • 148 CHAPTER FlvE Puttins WordsTogetherfrom a set of parental report measures called the MacArtbur'Bates Corumunicatiue De-ue lopment Inrrntorir, (Fenson et il,., 1994,2007), which provide highly reliable infor--riio., about children's language abilities at the early stages. These inuentories are nowavailable in 40 different langua[es and dialects. There is wide variability in the onset ofcombinatorial language. some children begin as early as fifteen months, the averageseems ro be at about .igh,.., monrhs, and by the age of two almost all children areproducing some word clombinations (Bates, Dale, & Thal, 1995). Although age itselfi, .ro. ,hJb.st predictor of language development since children develop at vastly dif-ferent rates, the length ofa child's sentences is an excellent indicator ofsyntactic devel-opment; each new.l.-.n, of syntactic knowledge adds length to a child's utterances.

    Roger Brown (1973) introduced a measure of the length of a child's utterancescalled thJ mean length of utterance (MLU), which has come to be widely used as anindex of syntacdc d;lopment in early childhood. MLU is based on the average lengthof a child's sentences ,.or.d on transcripts of spontaneous speech. Length is deter-mined by the number of meaningful units, or nxlr?hemes, rather than words' Mor-phemes includ. simple content words such as cat, Play, do, red; function words such as,0, thr, ryou, tbis;

    "nd ,ffi*., or grammatical inflections such as un-, -s, -ed.The addi'

    tion of each morpheme (or minimal unit carrying meaning) reflects the acquisition ofnew linguistic knowledge. So children who have similar MLUs are at the same level oflinguistic maturity, and their language is at the same level of complexiry.

    In order to calculate the MLU of a particular child, one needs a transcript of a half-hour conversation. The childt language must be divided into separate utterances, andthese utterances musr be divided inio morphemes. Brown (1973) provides detailed rulesfor judgingwhat consritures a morpheme for the child learning English (see Figure 5.4).

    ' il lJ"git"dinal studies, th. MLUs calculated at successive points in time gradu-ally increaselFigure 5.5 shows the MLU plotted against chronological age for the three.h'ildr.., studieJ by Brown and his colleagues. Clearly, MLU grows at different rates indifi[erent children. of the children followed by Brown, Eve's MLU rose most sharply,indicating very rapid language development, whereas sarah and Adam showed moregradual

    "ia t.s.o.rrirt.nt inc..me.rts in their MLU. Using the MLU' Brown subdi-

    iid.d ,h. major period of syntactic growth into five stags, beginning with Stage I,when the MLU i; between L.0 and 2.0. Successive stages are marked by increments of0.5. Thus, Stage II goes from 2.0 to 2.5; Stage-III is from 2.5 to 3.0; stage IV h t*3.0 to 3.5;

    "rrJ s."g. v is from 3.5 to 4.0. Beyond an MLU of about 4.0, some of the

    assumptions or, *hi.h the measure is based are no longer valid, and longer sentencesdo noisimply reflect what the child knows about language; therefore, MLU loses valueas an index of language development after this stage'

    There are some quesrions rhat arise in calculating MLUs in foreign languages, es-pecially highly inflected and synthetic languages such as German, Russian, or Hebrew'ir, ,h.r. ."I.ri, becomes difficult to decide what functions as a morpheme in the child'sspeech, and it is easy to obtain inflated numbers. Still, there have been attemPts toot.rrd the concept of MLU to structurally varied languages (Bowerman, 1973) ot tomodify the measu.e to accounr for cross-linguistic differences (Dromi & Berman,

  • Meosuring Syntoctic Growth 149: I r,.t.j.,i.:.,ii_..,,-i._lt.:rt.,1",.. .-

    nolesfor,celcutoting megn.lengrh of uirenin '-rl4;p-in1i4 by. .

    permission of the publishers from A First lnnguoge by RogerBrown, Combridge. MA: Horvord University Press. Copyrighi':,! 973 by the'Presidenl ond Fellows o[ HorvoriJ College.] . '., ,', ' ,'

    1. Start with the second page of the transcription unless that page involves arecitation of some kind. In this latter case, start with the first recitation-freestretch. Count the first 100 utterances satisfring the following rules.

    2. Only fully transcribed umerances are used; none with blanls. Portions ofutterances, entered in parentheses to indicate doubtful ranscription, are used.

    3. Include all exact utterance repetitions (marked with a plus sign in records).Stuttering is marked as repeated efforts at a single word; count the word oncein the most complete form produced. In the few cases where a word isproduced for emphasis or the like (no, no, no) count each occurrence.

    4. Do not count such fillers as mm or oh, but do count no, yeah, and hi.5. All compound words (two or more free morphemes), proper names, and

    ritualized reduplications count as single words. Examples: birthday, rachety-boorn,choo-cboo, quach-quach, night-night, pochetbooh, see saw. Jrxtification is that noevidence that the constituent morphemes function as such for these children.

    6. Count as one morpheme all irregular pasts of the verb (got, did, went, sau).Justification is that there is no evidence that the child relates these to Presentforms.

    7. Count as one morpheme all diminutives (dogte, rtlomm!) because thesechildren at least do not seem to use the suffix productively. Diminutives arethe standard forms used by the child.

    8. Count as separate morphemes all auxiliaries (is, haue, will, can, rnast, uouA).Also all catenatives: gonna, wanna, hafia.These latter counted as singlemorphemes rather than x going to ot uant to because evidence is that theyfunction so for the children. Count as separate morphemes all inflections, forexample, possessive {$, plural {s}, third person singular {s}, regular pasc {di,progressive iing].

    9. The range count follows the above rules but is always calculated for the totaltranscription rather than for 100 ufierances.

    l9B2).In some languages, calculating the length of utterances in words, rather thanmorphemes, has proven to be quite useful (e.g., Hickey, 1991). By using a similar in-dex to chart language growth across a range oflanguages, we can search for the univer-sal and invariant features that characterize the main stages of syntactic development.

    Other measures of syntactic development have also been developed. One exam-ple is the Index of Productive Syntax (IPSyn), introduced by Hollis Scarborough(1989). For this measure one also needs a transcript of one hundred spontaneous

  • 150 GHAPTER FlvE Putting wordsTogether

    2.00

    u21 fi28?,J323,. 36 38Ago (in nronth3)

    speech urterancs from a child. Using the scoiesheet provided by Scarborough, the re-,.*r.h., marks the use, up to a maximum of two very different uses, of a variety ofstructures in four categories: in noun