CHAPITRE 4. CONCLUSION GÉNÉRALE
4.5 AVENUES DE RECHERCHE PROMETTEUSES
À la base de cette motivation à élucider des parcours de développement de plus en plus nuancés repose la conviction suivante : que la rigueur de la modélisation et des
méthodes d’analyses, combinée à des sources de plus en plus variées d’informations sur les facteurs liés au développement devrait permettre d’obtenir une description du
développement qui s’approche de la complexité de la réalité. Ces efforts de concertation obligent toutefois à une ouverture mutuelle de champs disciplinaires par ailleurs fortement ancrés dans des traditions de haute spécialisation. H ne s’agit plus de décrire le
comportement en le réduisant à ses composantes, qu’il s’agisse de facteurs physiologiques, génétiques, sociaux ou autres, mais bien d’intégrer les connaissances liées à chaque champ d’étude pour tracer un portrait qui sache faire place à la nuance et la rigueur.
Les approches privilégiant des analyses de parcours individuels à l’instar des parcours de groupe sur lesquels on s’est traditionnellement appuyé, offrent des avenues de recherche prometteuses à cet égard. H devient alors possible de décrire un ensemble de parcours de développement pour divers phénotypes sur une base longitudinale, du phénotype stable à celui qui s’avère transitoire, et d’identifier leurs déterminants. Des approches telles que celle de Nagan (1998), offrent d’importantes contributions méthodologiques à cet égard. La fréquence et la précision des mesures requises pour une description de plus en plus nuancée, risquent d’être onéreuses, mais le coût de recherches mal ciblées l’est peut-être encore plus. Les études présentées dans cette thèse font déjà l’objet d’un suivi longitudinal dans l’objectif de converger vers des descriptions ontogéniques qui s’approchent de plus en plus d’une description de la « réalité » du développement des phénotypes en question.
RÉFÉRENCES (CHAPITRE 1,2 et CONCLUSION)
Baker, L. et Cantwell, D P. (1977). Psychiatrie Disorder in Children with Speech and Language Retardation. Archives of General Psychiatry. 34. 583-591.
Baker, L. et Cantwell, D P. (1987). A prospective psychiatrie follow-up of children with speech-language disorders. Journal of American Academy of Child and Adolescent Psychiatry. 28, 739-748.
Baltaxe et Simmons, (1990). The differential diagnosis of communication disorders in child and adolescent psychopathology. Topics in Language disorders, 10, 17-31.
Bates, E. (in press). On the nature and nurture of language. To appear in R. Levi-Montalcini, D. Baltimore, R. Dulbecco, & F. Jacob (Series Eds.) & E. Bizzi, P. Calissano, & V. Volterra (Vol. Eds.), Frontiere della biología !Frontiers of biologyl. The brain of homo sapiens. Rome: Giovanni Trecanni.
Bates, E., & Goodman, J. C. (1997). On the inseparability of grammar and the lexicon: Evidence from acquisition, aphasia, and real-time processing. Language and Cognitive Processes, 12, 507-584.
Beitchman, J.H., Hood, J., Rochon, J. et Peterson, M. (1989). Empirical classification of speech-language impairment in children: II. Behavioral characteristics. Journal of American Academy of Child and Adolescent Psychiatry, 28, 118-123.
Beitchman, J.H., Wilson, B., Brownlie,E.B., Walters,H., Inglis, A. et Lancee, W. (1996). Long-term consistency in speech-language profiles: II. Behavioral, emotional and social outcomes. Journal of the American Academy of Child and Adolescent Psychiatry, 35(6), 815-825.
Bertasich, A.A., Curtiss, S. et Tallal, P. (1993). Language, learning and behavioural
disturbances in childhood: A longitudinal perspective. Journal of American Academy of Child and Adolescent Psychiatry. 32(3). 585-594.
Bishop, D. (1997). Pre-and Perintala hazards and family background in children with specific language impairments: A twin study. Brain and Language, 56, 1-26.
Boivin, M., Poulin, F. et Vitaro, F. (1994). Depressed mood and peer rejection in childhood. Development and Psychopathology, 6. 483-498.
Brinton, B. et Fujiki, M. (1993). Clinical forum: Language and social skills in the school-age population: Language, social skills amd socioemotional behavior. Language. Speech and Hearing Services in Schools. 24. 194-198.
Brown, R. (1957). Linguistic determinism and the part of speech. Journal of Abnormal and Social Psychology. 55. 1-5.
Campbell, S. B. (1994). Behavior problems in preschool children: A review of recent research. Journal of Child Psychology and Psychiatry. 36 (1), 113-149.
Campbell, S. B. et Ewing, L. J. (1990). Hard to manage preschoolers: Adjustment at age nine and predictors of continuing symptoms. Journal of Child Psychology and Psychiatry. 31. 871-889.
Campbell, S. B., March, C. L., Pierce, E. Ewing, L. J. et Szumowski, E. K. (1991). Hard-to- manage preschool boys: family context and the stability of externalizing behavior. Journal of Abnormal Child Psychology. 19. 301-310.
Campbell, S. B., Pierce, E., March, C. L., Ewing, L. J. et Szumowski, E. K. (1994). Hard-to- manage preschool boys: :symptomatic behavior accross contexts and time. Child Development. 65. 836-851.
problems in children. Dans S. Reiss et R. Bootzin (Eds). Theoretical issues in behavior therapy, (pp. 219-254). NY : Academic Press.
Caspi, A., Elder, G. H. et Bern, D. J. (1987). Moving against the world: Life course patterns of explosive children. Developmental Psychology, 23, 308-313.
Chess, S. et Rosenberg, M. (1974). Clinical différenciation among children with initial language complaints. Journal of Autism and Childhood Schizophrenia, 4. 99-109. Chomsky, N. (1995). The minimalist program. Cambridge, MA: MIT Press
Cicchetti, D. et Schneider-Rosen, K. (1986). An organizational approach to childhood depression. Dans M. Rutter, C.E. Izard et P.B. Read (Eds). Depression in young people: Developmental and clinical perspectives, (pp.71-134) NY : Guilford Press. Cole, J.D. & Dodge, K.A. (1998). Aggression and antisocial behavior. In W. Damon & N.
Eisenberg (Eds), Handbook of Child Psychology : Social, emotional and personality development, (vol. 3, pp. 779-862). Toronto : Wiley.
Craig, H.K. (1993). Social skills of children with specific language impairment: Peer relationships. Language, Speech and Hearing in the Schools, 24, 206-215.
Crowther, J. K., Bond, L. A. et Rolf, J. E. (1981). The incidence, prevalence and severity of behavior disorders among preschool-age children in day care. Journal of Abnormal Child Psychology, 9, 23-42.
Cummings, E. M., Iannotti, J.J. et Zahn-Waxier, C. (1989). Aggression between peers in early childhood: Individual continuity and developmental change. Child Development.
Cyphers, L.H., Phillips, K., Fulker, D. W. et Mrazek, D.A. (1990). Twin temperament during the transition from infancy to early childhood. Journal of the American Academy of Child and Adolescent Psychiatry, 29 (3), 392-397.
Dale, P.S., Simonoff, E., Bishop, D., Eley, T., Oliver, B., Price, T., Purcell, S., Stevenson, J. et Plomin, R. (1998). Genetic influence on language delay in two-year-old children. Nature Neuroscience. 1(4), 324-328.
Dale, P.S., Dionne, G., Eley, T. et Plomin, R. (2000). Lexical and grammatical development: A behavioural genetic perspective. Journal of Child Language, 27, 619-642.
DeFries, J.C. et Fulker, D.W. (1988). Multiple regression analysis of twin data: Etiology of deviant scores versus individual differences. Acta Geneticae Medicae et
Gemellologiae, 37, 205-216.
Dodge, K. A. (1990). Nature versus nurture in childhood conduct disorder: it is time to ask a different question. Developmental Psychology, 26, 698-701.
Donnellan, A.M., Mirenda, P.L., Messaros, R.A., et Fassbender, L.L. (1984). Analyzing the communicative function of aberrant behavior. Journal of the Association for the Severely Handicapped, 9, 201-212.
Earls, F. (1987). On the family transmission of child psychiatric disorder. Journal of Child Psychology and Psychiatry, 28, 791-802.
Egeland, B., Kalkoske, M., Gottesman, N. et Erikson, M. F. (1990). Preschool behavior problems, stability and factors accounting for change. Journal of Child Psychology and Psychiatry. 31, 891-909.
Emde, R. N., Plomin, R., Robinson, J. L, Corley, R., DeFries, J., Fulker, D. W., Reznick, J. S., Campos, J., Kagan, J et Zahn-Waxler, C. (1992). Temperament, emotion and
cognition at fourteen months: The Mac Arthur Longitudinal Twin Study. Child Development. 63. 1437-1455.
Fagot, B. I. (1984). The consequences of problem behaviors in toddler children. Journal of Abnormal Child Psychology. 12. 385-395.
Fletcher, (1987). Aspects of language development in the preschool years. Dans W. Yule et M. Rutter (Eds), Language development and disorders, (pp. 70-89). Clinics in
Developmental Medicine, London : MacKeith Press-Blackwell Scientific.
Fundudis, T., Kolvin, I. et Graside, R.F. (Eds) (1979). Speech retarded and deaf children: Their psychosocial development. London : Academic Press.
Gagnon, C. (1989). Comportements agressifs dès le début de la fréquentation scolaire. Apprentissages et socialisation. 21 (1), 9-18.
Ganger, J., Pinker, S., Baker, A., & Chawla, S. (1999). Heritability of early milestones of vocabulary and grammar: A twin study. Manuscript submitted for publication. Giddan, Milling et Campbell, S. (1996). Unrecognized language and speech deficits in
preadolescent psychiatric inpatients. American Journal of Orthopsychiatry. 66(1). 85-
92.
Goldberg, A. E. (1995). Constructions: A construction grammar approach to argument structure. Chicago, IL: University of Chicago Press.
Goodenough, R. L. (1931). Anger in young children. Minneapolis : University of Minnesota Press.
Goodman, H., Gottlieb, J. et Harrison, I. (1972). Social acceptance of EMR’s integrated into anon-graded elementary school. American Journal of Mental Deficiency. 76, 412-417.
Gualtieri, C.T., Koriath, U., Van Bourgondein, M. et Saleeby, N. (1983). Language disorders in children referred for psychiatric services. Journal of American Academy of Child and Adolescent Psychiatry, 22. 580-587.
Hinshaw, S. P. (1992). Externalizing behavior problems and academic underachievement in childhood and adolescence: Causal relationships and underlying mechanisms.
Psychological Bulletin. Ill (1), 127-155.
Hurlock, E. B. (1978). La psychologie du développement. Montreal. McGraw-Hill.
Jenkins, S., Bax, M. et Hart, H. (1980). Behaviour problems in preschool children. Journal of Child Psychology and Psychiatry, 21, 5-17.
Keenan, K. et Shaw, D.S. (1993). The development of aggression in toddlers: A studyu of low income families. Journal of Abnormal Child Psychology, 22. 53-77.
Keenan, K. et Shaw, D.S., (1996). Similarities and differences in developmental trajectories of boys' and girls' early behavioral problems. Communication présentée au congrès biannuel de !'International Society for the Study of Behavior and Development, Québec, Qc. Août, 1996.
Koot, H. M. (1993). Problem behavior in Dutch preschoolers. Thèse de doctorat inédite, Erasmus University, Rotterdam.
Larzelere, R. E., Amberson, T. G. et Martin, J. A. (1992). Age differences in perceived discipline problems from 9 to 48 months. Family Relations. 41. 192-199.
Lee, C. et Bates, J. E. (1985). Mother-child interaction at age two years and perceived difficult temperament. Child Development, 56, 1314-1325.
Locke, J. L. (1997). A theory of neurolinguistic development. Brain and Language. 58, 265- 326.
Loehlin, J. C. (1996). The Cholesky approach: A cautionary note. Behavior Genetics. 26. 1, 65-69.
Maccoby, E. E. et Martin, J. A. (1983). Socialization in the context of the family: Parent- child interaction. Dans P. H. Müssen et E. M. Hetherington (Eds.), Handbook of child psychology: Socialization, personality and social development, (pp. 1-101). NY : Wiley.
Marlow, (1987). Prelinguistic Communication. Dans W. Yule et M. Rutter (Eds), Language development and disorders, (pp. 53-69). Clinics in Developmental Medicine, London : MacKeith Press-Blackwell Scientific.
Martin, J. (1981). A longitudinal study of the consequence of early mother-infant
interaction: A microanalytic approach. Monographs for the Society for Research in Child Development, 46 (3, 190).
Mason, D. A. et Frick, P. J. (1994). The heritability of antisocial behavior: A meta-analysis of twin and adoption studies. Journal of Psychopathology and Behavioral Assessment.
16 (4), 301-323.
Maynard, D.W. (1988). Language, interaction and social problems. Social Problems, 35. 311-334.
McGee, R., Partridge, F., Williams, S. et Silva, P. A.(1991). A twelve year follow-up study pf preschool hyperactive children. Journal of the American Academy of Child and Adolescent Psychiatry, 30, 224-232.
Miles, D.R. & Carey, G. (1997). Genetic and environmental architecture of human aggression. Journal of personality and social psychology, 72 (1), 207-217.
Moffit, T. E. (1990). Juvenile delinquency and attention deficit disorder: Boys’
developmental trajectories from age 3 to age 15. Child Development, 61, 391-404. Naigles, L. G. (1990). Children use syntax to learn verb meanings. Journal of Child
Language. 17, 357-374.
Neale, M.C. (1999). The MX statistical package, http://www.vipbg.vcu.edu/~mx/mxgui/. Neale, M. et Cardon, L.R. (1992). Methodology for the Genetic Study of Twins and Families
Dordrecht : Kluwer Academic Publishers.
Nelson, K.E. (1981). Toward a rare-event cognitive comparison theory of syntax acquisition. Dans P. Dale & D. Ingram (Eds), Child language: An international perspective, (pp. 229-240). Baltimore: University Park Press,.
Oberklaid, F., Sanson, A., Pedlow, R. et Prior, M. (1993). Predicting preschool behavior problems from temperament and other variables in infancy. Pediatrics, 91 (1), 113-
120.
O’Grady, W. D. (1987). Principles of grammar and learning. Chicago, EL: University of Chicago Press.
Olds, S. W. et Papaba, D. E. (1996). Le développement de la personne. Laval, Qc : Éditons études vivantes.
Parke, R. et Slaby, R. (1983). The development of aggression. Dans P. H. Müssen et E. M. Hetherington (Eds), Handbook of child psychology: Socialization, personality and social development, (pp. 547-641). NY : Wiley.
Patterson, G. R. (1982). Coercive family processes. Eugene, OR : Castalia.
Patterson, G. R. (1988). A replication of a model for preadolescent boys' depressed moods. Manuscrit inédit. Oregon Social Learning Centre, Eugene, OR.
Patterson, G. R., Reid, J. B. et Dishion, T. (1992). Antisocial Boys. Eugene, OR : Castalia Piaget, J. (1977). La naissance de !,intelligence chez l’enfant. 9e édition. Neuchâtel, Suisse :
Delachaux et Niestlé.
Piel, J.A. (1990). Unmasking sex and social class differences in childhood aggression: The case for language maturity. Journal of Educational Research, 84 (2). 100-106.
Plomin, R. et Daniels, P. (1987). Why are children in the same family so different? Behavioral and Brain Sciences. 10. 1-16.
Price, T. S., Eley, T.C., Dale, P.S., Stevenson, J. & Plomin, R. (2000). Genetic and environmental covariation between verbal and nonverbal cognitive development in Infancy. Child Development, 71 (4), 948-959.
Prior, M., Smart, D., Sanson, A., et Oberklaid, F. (1993). Sex differences in psychological adjustment from infancy to 8 years. Journal of the American Academy of Child and Adolescent Psychiatry, 32 (2), 291-304.
Prior, M., Smart, D., Sanson, A., Pedlow, R. et Oberklaid, F. (1992). Transient versus stable behavior problems in a normative sample: Infancy to school age. Journal of Pediatric Psychology, 17, 423-443.
Richman, N., Stevenson, J. et Graham, P. J. (1982). Preschool to school: A behavioral study. London : Academic Press.
Rende, R. D. (1993). Longitudinal relations between temperament traits and behavioral syndromes in middle childhood. Journal of the American Academy of Child and Adolescent Psychiatry, 32 (2), 287-290.
Reznick, J. S., Corley, R. & Robinson, J. (1997). A longitudinal twin study of intelligence in the second year. Monographs of the Society for Research in Child Development, 62 (1, Serial No. 249).
Rothbart, M. et Bates, J.E. (1998). Temperament. Dans Damon et Eisenberg, (Eds),
Handbook of Child Psychology: Social, emotional and personality development, (pp 105-176). NY : Wiley and Sons,.
Rowe, D.C. (1994). The limits of family influence: Genes, experience and behavior. New York : Guilford Press.
Rutter, M. (2000). Language development delays in twins. Communication présentée à ΓUniversité Concordia, Montréal. Mars 2000.
Rutter, Μ. (1987). Temperament, personality and personality disorder. British Journal of Psychiatry, 150. 443-458.
Rutter, M. (1997). Nature-nurture integration: The example of antisocial behavior. American Psychologist, April 1997, 390-398.
Sameroff, A. J. et Chandler, M. J. (1975). Reproductive risk and the continuum of caretaking casuality. Dans F. D. Horowitz, M. Hetherington, S. Scarr-Salapatek et G. Siegel (Eds), Review of Child Development Research, (pp. 187-249). Chicago : University of Chicago Press.
Sanson, A., Smart, D., Prior, M. et Oberklaid, F. (1993). Precursors of hyperactivity and aggression. Journal of the American Academy of child and adolescent psychiatry, 32 (6), 1207-1216.
Schmitz, S. & Fulker, D.W. (1996). Communication présentée au congrès biannuel de !,International Society for the Study of Behavior and Development, Québec, Qc. Août, 1996.
Schonfeld, Shaffer, O’Connor et Portnoy, (1988). Conduct disorder and cognitive functioning: testing three causal hypotheses. Child Development, 59. 993-1007. Shaw, D. S., Keenan, K. et Vendra, J.I. (1994). Developemental precursors of externalizing
behavior: Ages 1 to 3. Developmental Psychology, 30 (3), 355-364.
Silva, P.A. (1987). Epidemiology, longitudinal course and some associated factors : An update. Dans W. Yule et M. Rutter (Eds), Language development and disorders, (pp.
1-15). Clinics in Developmental Medicine, London : MacKeith Press-Blackwell Scientific.
Silva, P.A. et Williams, S.M. (1983). Developmental delay from three to seven years and its significance for low intelligence and reading difficulties at age seven. Developmental Medicine and Child Neurology, 26. 299-313.
Stevenson, J. (1996). Developmental changes in the mechanisms linking language disabilities and behaviour disorders. Dans J. H. Beitchman, N. Cohen, M.M. Konstantereas, et R. Tannock (Eds), Language, learning and behavior disorders. Cambridge: Cambridge University Press.
Stevenson, J., Pennington, BE, Gilger, J.W., DeFries, J.C. & Gillis, J. J. (1993).
Hyperactivity and spelling disability - testing for shared genetic etiology. Journal of Child Psychology and Psychiatry, 34, 1137-1152.
Stevenson, J. et Richman, N. (1976). The prevalence of language delay in a population of three year old children and its association with general retardation. Developmental Medicine and Child Neurology. 18. 431-441.
Stevenson, J., Richman, N. et Graham, P. (1985). Behavior problems and language abilities at three years and behavioural deviance at eight years. Journal of Child Psychology and Psychiatry, 26(2), 215-230.
Tremblay, R. E. (2000). The development of aggressive behaviour during childhood: What have we learned in the past century?. International Journal of Behavioural
Development. 24 (2), 129-141.
Tremblay, R.E. et Boulerice, B. (1998). Socioeconomic, neighborhood, familial and individual determinants of physical aggression in female and male children: The National Longitudinal Survey of Children and Youth in Canada. Communication présentée au XVe Congrès biannuel de !'International Society for the Study of Behavior and Development. Bernes, Suisse. Juin 1998.
Tremblay, R.E., Boulerice, B., Harden, P.W., McDuff, P., Pérusse, D., Pihl, R.O. et Zoccolillo, M. (1996). Do children in Canada become more aggressive as they approach adolescence? Dans Human Resources Development Canada & Statistics Canada (Eds), Growing up in Canada: National Longitudinal Survey of Childrena nd Youth, (pp. 127-137). Ottawa : Statistiques Canada.
Van den Oord, Verhulst et Boomsma, D. (1996). A genetic study of maternal and paternal ratings of problem behaviors in 3 year-old twins. Journal of Abnormal Psychology,
Warr-Leeper, G., Wright, N. et Mack, A. (1994). Language Disabilities of antisocial boys in residential treatment. Behavioral Disorders, 19(3), 159-169.
Zahn- Waxier, C., Iannotti, R. J. Cummings, E. M. et Denham, S. (1990). Antecedents of problem behaviors in children of depressed mothers. Development and
Running head: VOCABULARY AND GRAMMAR
Lexical and Grammatical Development: A Behavioural Genetic Perspective
Philip S Dale
University of Missouri, Columbia Ginette Dionne
Université Laval, Québec Thalia C Eley & Robert Plomin
Institute of Psychiatry, London
Author Note
Philip S. Dale, Department of Communication Science and Disorders; Ginette Dionne, École de psychologie; Thalia C. Eley and Robert Plomin: Social, Genetic and Developmental Psychiatry Research Centre.
We thank the parents of the twins in the Twins Early Development Study (TEDS) for making the study possible. TEDS is supported by a programme grant from the UK Medical Research Council. The authors thank Dorothy Bishop for her comments on an earlier draft of the manuscript.
Address for correspondence: Philip Dale, Department of Communication Science & Disorders, University of Missouri-Columbia, Columbia, MO 65211. Electronic mail may be sent via internet to dalep@health.missouri.edu.
Abstract
The relation of lexical and grammatical knowledge is at the core of many controversies in linguistics and psycholinguistics. Recent empirical findings that the two are highly correlated in early language development have further energized the theoretical debate. Behavioral genetics provides an illuminating new tool to explore this question, by addressing the question of whether the empirical correlation simply reflects the fact that environments which facilitate one aspect of language growth also facilitate the other, or whether the same underlying acquisition mechanisms, influenced by the same genes, are responsible for the correlation. We explored this issue in a study of 2898 pairs of two-year-old twins bom in England and Wales. Language development was assessed by their parents using an adapted version of the MacArthur Communicative Development Inventory which assesses
vocabulary and grammar. Moderate heritabilities were found for both. As in previous studies, measures of vocabulary and sentence complexity were substantially correlated (r = 0.66). Behavior-genetic modeling of the relation of vocabulary and grammar produced an estimated value of 0.61 for the genetic correlation, a measure of the overlap of the genetic effects that contribute to the two aspects of language development. In contrast, a measure of nonverbal cognitive development, the PARCA, was only weakly correlated at both the phenotypic level and at the level of genetic correlations with the language measures. Thus, although the distinction between verbal and nonverbal skills has a genetic basis underlying the phenotypic dissociation, there is little evidence either genetically or phenotypically for a dissociation between vocabulary and grammar within language.
Lexical and Development: A Behavioural Genetic Perspective INTRODUCTION
The relation of lexical and grammatical knowledge is at the core of many controversies in linguistics and psycholinguistics, among them the autonomy of syntax, modularity of mind, the relative utilization of cues in sentence comprehension by adults, and the nature of bootstrapping in language acquisition. Historically the two types of knowledge have been viewed as qualitatively distinct, but in both fields more recently there have been proposals which integrate the two. For example, within linguistic theory there is a chain of development from Lexical Functional Grammar (Bresnan, 1982) through Construction Grammar (Goldberg, 1995) and the Minimalist Program (Chomsky, 1995) in which the distinction between grammar and lexicon has steadily disappeared. Within cognitive
psychology, many if not most versions of connectionism (Elman, Bates, Johnson, Karmiloff- Smith, Paris! & Plunkett, 1996) posit a single mechanism for both domains.
Recent findings that the two aspects of development are highly correlated in early language development have further energized the theoretical debate (Fenson, Dale, Bates, Reznick, Thai, & Pethick, 1994; Bates, Dale & Thai, 1995; Bates & Goodman, 1997). Both the emergence of word combinations and the succeeding development of specific
grammatical features appear to be more highly correlated with vocabulary size than with, e.g., age. It is not just that a certain level of vocabulary development is necessary for combinatorial development; based on the large norming sample for the MacArthur
Communicative Development Inventories, it is very nearly sufficient as well. As shown in Figure 16 of Fenson et al., 1994, there are almost no cases of children with very large vocabularies who still use minimal, telegraphic speech. Almost never is a large vocabulary
found without combinatorial language. Such a finding contrasts strongly with the relation of vocabulary production and comprehension. Though these two skills are related, it is not unusual for a large comprehension vocabulary to be found in conjunction with a small or even nonexistent production vocabulary (compare Figures 14 and 16 of Fenson et al, 1994).
Several explanations have been offered for this close relation (Bates et ah, 1995; Bates & Goodman, 1997). They include the following:
1. A sufficient stock of content words is a necessary foundation for solving the
segmentation problem, especially for the perception and identification of unstressed grammatical forms.
2. As children move from learning nouns (primaries, in O’Grady’s (1987) logical taxonomy of lexical items) to learning relational words (secondaries: verbs and adjectives) which depend on a relation with one or more primaries to the learning of closed-class words (tertiaries: prepositions, pronouns, conjunctions) which presuppose or depend upon at least one secondary relationship, they are essentially performing the same kind of