Description of the Research Enterprise
Donna Thal, Ph. D.
Principal Investigator and Laboratory Director

The purpose of research conducted in this lab is to identify reliable early predictors of risk for language impairment in young children and to explore relationships between language and nonlinguistic cognition. The research focuses on early identification of risk for language disorder and learning disabilities by building on data which suggest different courses of development for children with expressive only versus expressive and receptive language delays. Motivation for the research includes studies in which predictors of risk were identified in late-talking toddlers (Thal & Bates, 1988; Thal, Tobias & Morrison, 1991; Thal & Tobias, 1992, 1994), studies of toddlers with congenital focal brain injury which suggest potential brain development explanations for differences found in comprehension and production (Thal, Marchman, Stiles, Trauner, Nass, Aram, & Bates, 1991), and reports of changes in brain structure in this period which suggest that it may be an optimal time for intervention (see Bates, Thal, Finlay, & Clancy, in press; Thal & Clancy, in press). Exploration of the relationships between language and specific nonlinguistic cognitive processing abilities provides tests of theories of language development. Thus, the work has both clinical and theoretical significance.

Clinical Significance

Studies carried out in this laboratory are designed to identify, in a specific and quantifiable manner, predictors of clinically significant delay in the earliest phases of communicative development. There are three clinical foci:

Early markers of risk for language impairment. In studies of children between 18 and 28 months of age, two profiles of early communicative development that may differentiate a subset of late talkers who do not "catch up" from another which does have been identified (Thal, Tobias & Morrison, 1991; Thal & Tobias, 1992). They include delays in vocabulary comprehension and in the use of communicative and symbolic gestures. Other work (Thal, Bates, Goodman & Jahn-Samilo, 1997) suggests that even earlier delays in use of communicative gesture and language comprehension may predict risk for continued delay. Earlier findings indicating that 40 to 60 percent of children with early communicative delay are at risk for later language or learning disability (Rescorla & Schwartz, 1989), more recent contradictory findings (Paul 1996, 1997), and current social policy (Education of the Handicapped Amendments, Public Law 99-457 and Individuals with Disabilities Education Act, Public Law 102-119), which requires speech language pathologists to diagnose and treat children from birth to 3 years of age, point to the importance of accurate early diagnosis. The studies carried out in this lab are designed to explore the differential contributions of language production, language comprehension, gesture production, and genetic and demographic variables to accurate early identification of risk for language disorder and learning disability.

Development of symptoms over time. The research carried out in this laboratory employs a prospective approach to studying the earliest stages of communicative development. In the previous years the focus was on development from first words to early stages of grammar. Current studies focus on pushing the starting age of observation back to 10 months of age, a point at which the transition from prelinguistic to linguistic communication usually begins in normal children. Late talkers are identified in very early the process of expressive language development (16 months of age) and followed into the early stages of grammatical development. This will allow us to characterize disordered language acquisition from the earliest point to date. We are also searching for predictors of later risk at the early stages of intentional communication (10 months), describing those predictors from the period in which the fundamentals of language are laid down in normal children. This longitudinal strategy is particularly important from a clinical point of view. As noted above, it will provide valuable information about the course of development, i.e., the processes involved in catching up or falling behind. Since important changes in brain and behavior take place between 0 - 4 years, this is the age range in which we stand the greatest chance of making a difference. Detailed understanding of the differential paths taken to normal and disordered language use will have a major impact on early assessment and intervention.

Reliable and time-efficient tools. Clinical assessment of early communication skills has been a time consuming and imprecise process. Screening tools that might be used by pediatricians and other busy health professionals to determine if referral is appropriate are weak at best. Procedures that provide better estimates of infants' true communication skills are too time consuming and specialized for systematic use with large numbers of children. The development, validation and norming of the MacArthur Communicative Development Inventories (CDIs, Fenson et al., 1993) in English, and the FundaciÛn MacArthur: Inventarios del Desarrollo de Habilidades Comunicativas (Maldonado, Thal, & Bates, 1993) in Spanish, provide a solution to this problem. Studies in the Developmental Psycholinguistics Laboratory are designed to use the CDIs to obtain detailed longitudinal data on communication (vocabulary comprehension and production, gesture production, and grammatical complexity) in English and Spanish-speaking children from 10 to 36 months of age. By validating results against laboratory data and providing rapid feedback to participating pediatricians regarding their patients' development, we intend to make pediatricians more aware of early communication skills and how to make appropriate early referrals.

Linguistic/Psycholinguistic Significance

The research carried out in the Developmental Psycholinguistics Laboratory, and collaborating laboratories at San Diego State University, and the University of California, San Diego, focus on the search for patterns of association and dissociation between language and other aspects of cognition and information processing in children with normal and delayed onset of communication skills. Aside from its clinical value, this methodology is designed to answer questions about one of the most controversial issues in Western intellectual history: To what extent can we view language as an independent system, logically and causally unrelated to other intellectual functions? This is an issue that, in its original formulation, goes back at least to ancient Greece. By focusing on children at an extreme end of the normal distribution, we have begun to learn more about the extent to which language and various aspects of nonlinguistic cognition can "come apart" across the course of development (Thal & Bates, 1988; Thal et al., 1991; Thal & Tobias, 1992; Thal & Tobias, 1994; Thal, Bates, Zappia & Oroz, 1996; Thal, et al, 1997; Gershkoff-Stowe, Thal, Smith & Namy, 1997). These results have convinced me and my colleagues that further comparison of language comprehension and production to more narrowly defined measures of gesture production (symbolic or nonsymbolic, communicative or noncommunicative) will be the most productive direction to take for the next set of studies in the lab. Using the CDIs we can now focus on much larger numbers of subjects, and describe their early communicative behavior in much greater detail than was possible in earlier laboratory studies. We will also continue to use the same productive multiple control group (language- and age-matched) design and the methodology of searching for associations and dissociations between language and nonlinguistic cognition in both behavioral and parental report studies.