Need for Translational Research on Early Language Development

Thus, there is a pressing clinical need for accurate, detailed information on multiple aspects of early typical and atypical language functioning and the diverse cognitive, behavioral, and contextual factors that affect them. In response, the NIH has recently called for collaborative translational (“bench to bedside”) research on basic developmental processes in both typical and atypical populations to better inform and guide clinical practice with children with developmental disorders, including language impairment, and to encourage basic behavioral scientists to seek a further understanding of how behavioral processes (such as language) are altered by developmental disorders. Until recently, however, advancement in collaborative translational language research has been hampered by fragmentation among multidisciplinary fields, related funding constraints, and poor communication among investigators from different disciplines (McCardle, Cooper, & Freund, 2005; Nelson et al., 2002; Rice & Warren, 2005b).

Most extant research on early language acquisition in children with language disorders has focused on a narrow range of language behaviors (e.g., vocabulary or morphosyntax) within one specific clinical group (e.g., Down syndrome, autism, or specific language impairment), describing single deficits relative to various control groups or evaluating within-group profiles of specific linguistic and cognitive skills within a particular group (Rice & Warren, 2005a; Rice, Warren, & Betz, 2005). Despite this limited focus, this research has provided a wealth of valuable information about the nature and process of those particular aspects of language development in specific populations. Results of profile analyses within different populations have been especially helpful in debunking stereotypes about different etiologic groups and have highlighted methodological caveats for future research, including the need for longitudinal research and the continued need to evaluate multiple dimensions of language (e.g., vocabulary/semantics, grammar/syntax, and pragmatics) in diverse groups. This research has also fueled and sparked continuing debates among researchers regarding the age-old philosophical question of the ontogenetic association between language and cognition (e.g., Elman et al., 1996; Karmiloff-Smith & Thomas, 2003; Thelen & Bates, 2003).

For illustrative purposes, a brief summary of some of the key research findings for four clinical groups of children with delayed or disordered language development that have been investigated intensively (Down syndrome, autism spectrum disorders, Williams syndrome, and specific language impairment) is provided here. This summary is not meant to be exhaustive.

Cross-Population Studies

Given the momentum in genetic and biobehavioral investigations within particular language disorders during the past decade, Rice and colleagues have recently heralded the need for further collaborative cross-population research to document the ways in which language disorders are manifest across clinical conditions (see Rice et al., 2005; Rice & Warren, 2004). Such research could lead to a deeper understanding of the commonalities and differences across conditions, the specific symptom profiles associated with each condition, and how general intellectual impairment with a specific genetic basis may affect the process of language acquisition in multiple domains. Cross-population comparisons would also facilitate the identification of subtypes of disability within diverse clinical conditions and enhance our ability to identify early in development young children who are likely to develop clinically significant language-learning problems (Reilly, Losh, Bellugi, & Wulfeck, 2004; Thal et al., 2004). In turn, the documentation of subtypes and the specific contextual factors associated with individual differences within conditions would augment our understanding of the different levels of risk that may predispose very young children in different groups for persistent language impairment. More generally, such research would contribute to our understanding of the nature and variability possible in human language development and would enhance our understanding of the brain bases of language and language development (Rice & Warren, 2004; Thal et al., 2004).

Although cross-population studies of language disorders are relatively rare to date, those that exist have raised some important questions and offered a few surprises. For instance, in a series of comparative studies conducted by a multidisciplinary group of collaborators in San Diego, aspects of children's language processing and acquisition were evaluated across several clinical populations at different ages. The clinical groups included “late-talking” toddlers, children with early focal brain injuries in either the right or left hemisphere (similar to those observed in adult aphasia patients), children with Williams syndrome, children with Down syndrome, and school-aged children with a diagnosis of specific language impairment, as well as appropriate typically developing controls (Bates, 2003).

For instance, in a longitudinal study comparing the lexical and syntactic development of late-talking toddlers, children with early focal brain injury, and typically developing children from 2 to 3 years of age (Thal et al., 2004), a number of interesting findings were reported. First, children in both at-risk groups exhibited significant delays in both vocabulary and grammatical development at both ages, and exhibited greater variability in language functioning than typical children (see also Kennedy, Sheridan, Radlinsky, & Beeghly, 1991). Second, different longitudinal associations between language comprehension and syntactic development were observed in each group, suggesting that different language skills may be organized differently in specific clinical groups. Third, qualitative analyses indicated that the at-risk groups produced the same kinds of errors (despite relative delays). However, the late talkers produced a substantially greater proportion of errors in obligatory contexts than did children with early focal brain injury, a pattern consistent with that observed in older children with specific language impairment.

In several other studies from the San Diego collaborative group, the linguistic and pragmatic skills of school-aged children in different clinical groups were compared (Marchman, Saccuman, & Wulfeck, 2003; Reilly et al., 2004; Weckerly, Wulfeck, & Reilly, 2003; Wulfeck et al., 2004). Results showed that, by school age, children with early focal brain injury performed in the normal range on most language measures, regardless of lesion size or location, and outperformed children with specific language impairment. These findings shed light on the extent and nature of brain plasticity and recovery for language functioning in these groups. In addition, contrary to expectations, specific morphosyntactic measures of the children with specific language impairment with no frank neurological impairment clustered with those of the children with Williams syndrome, who were moderately retarded. Moreover, the performance of children with Williams syndrome on these language tasks was solidly linked to mental age (and often resembled that of children with specific language impairment), suggesting that children with Williams syndrome are not “language savants,” at least for the measures evaluated in these studies, as several investigators in early studies have claimed (Bates, 2003). Reilly et al.'s (2004) results also highlight aspects of language and discourse that may be dissociable.

Contrasting results regarding the morphosyntactic development of children with Williams syndrome have been reported by other researchers (Clahsen & Almazan, 1998), which may reflect, in part, methodological differences across studies. For instance, Rice and others reported that 7-year-olds with Williams syndrome performed at near ceiling level in an elicited production task of finiteness morphemes, in contrast to the lower performance of language-matched children with specific language impairment and typical children (Rice, 2003).

In another series of cross-population studies, Tager-Flusberg and colleagues (see Tager-Flusberg, 2004a, for a review) demonstrated that a subgroup of children with autism with language impairment and language-matched children with specific language impairment exhibited a strikingly similar pattern of language skills. Children in both groups exhibited similarly poor performance and error patterns on tasks of nonword repetition and finite-verb morphology, suggesting that these children may share similar deficits in phonological processing and morphosyntactic knowledge. At the same time, children in both groups exhibited a relative sparing of articulation skills and verbal fluency. Interestingly, neuropathological findings in these groups are consistent with these language findings, suggesting the possibility of a common genetic etiological pathway to language disorder in the two groups (Tager-Flusberg, 2004a).

Need for Longitudinal Research

Further longitudinal studies of multiple aspects of language development in different clinical populations of children with language disorders are needed, especially during the period of time in ontogeny when language is acquired (Bates, 2003). Although costly and time consuming, such studies will allow us to evaluate the manner in which specific language behaviors in different domains emerge and change over time within different groups, and their potential linkages at various ages with genetic and neurocortical functions (Karmiloff-Smith & Thomas, 2003; Tallal & Benasich, 2002), higher order cognitive and socioemotional processes, and biological and social risk and resilience factors. Longitudinal designs will also allow us to evaluate within-group individual differences in profiles of language, cognitive, and behavioral skills over time, and describe the language phenotypes of subgroups of children more clearly and precisely (Tager-Flusberg, 2004b). Such research is critically needed to support and inform emerging studies evaluating the genetic and neurobiological etiology of different developmental language disorders.

To illustrate this need, Lord et al. (2004) noted that investigators in many prior studies of autism have tended to use general measures of verbal functioning (usually as control measures when evaluating the effect of autism on other cognitive or social skills such as theory of mind or central coherence). As a result, little is known about variations in different aspects of language (e.g., phonologic, semantic, morphosyntactic, pragmatic) among verbal children with autism, or (especially) how profiles among these different skills may change from early to later childhood. For instance, it is currently unclear whether children in the autistic spectrum disorders (or subgroups within this category) exhibit unique trajectories of language development from early to later childhood. Lord et al. contended that further understanding of the nature of these trajectories will have important implications for our understanding of the etiology and nature of developmental change within the autistic spectrum disorders, and children's potential response to treatment within this population.

In a rare long-term longitudinal study, children with autism exhibited an uneven developmental trajectory of their language and cognitive skills from the preschool period to adolescence (Sigman, 2005). Although about one-third of the children with autism made dramatic gains in cognitive and language skills from the preschool to the mid-school period, these gains had diminished dramatically (to less than half the change in their chronological age) by adolescence. Moreover, adolescents with autism and mental retardation exhibited almost no language gains. Notably, significant predictors of children's language functioning in adolescence were children's earlier functional play skills, responsiveness to others' bids for joint attention, and the frequency of requesting behaviors during the preschool period.

Further longitudinal studies in autism and other clinical populations are needed to shed light on how specific verbal and nonverbal cognitive and behavioral measures may be associated (or dissociated) at various points in time in ontogeny, and how functioning in different cognitive or socioemotional domains may support or derail language functioning in particular conditions or subgroups. An example of this type of longitudinal study comes from Mundy's programmatic research (see Mundy et al., 1993, for a review). In a 13-month longitudinal study of children with autism, Mundy et al. (1990) assessed the joint attention skills, pretend play behaviors, and language abilities of young children with autism and language-matched, mentally retarded children. All children were less than 5 years of age and were matched on receptive and expressive language age (M = 12.5 and 13.6 months, respectively). At the initial observation, joint attention deficits (but not requesting deficits) were observed in the children with autism, before functional or symbolic play deficits were observed in this sample. Of note, joint attention deficits were also observed for the children with autism at the follow-up visit, when play deficits were present. Moreover, children's initial joint attention (but not requesting) scores significantly predicted their symbolic play abilities at the time of the follow-up visit in the mentally retarded sample and approached significance in the autistic sample.

Mundy et al. (1990) speculated that nonverbal communicative and symbolic skills (i.e., joint attention and symbolic play skills) share a common source of variance and hypothesized that each may contribute to the development of children's language and social–cognitive and theory of mind abilities. Of note, Baron-Cohen, Allen, and Gillberg (1992) provided corroborative evidence that the joint attention and symbolic play deficits of children with autism are lawfully related. In their autism screening studies, the majority of toddlers who showed impairments in both joint attention skills and symbolic play in the second year received a diagnosis of autism later in childhood. In contrast, none of the toddlers who had deficits in only one domain or who had no deficits were diagnosed with autism.

Taken together, these findings suggest that joint attention skills precede the emergence of language and nonverbal symbolic play skills in children with autism, and may share variance with factors associated with the subsequent emergence of verbal and nonverbal symbolic functioning. Moreover, these results indicate that the type of associations and dissociations among cognitive and socioaffective behaviors associated with language development in children with autism may change in ontogeny.

Longitudinal cross-population studies such as these are necessary if we are to capture the dynamic, changing nature of language learning and its correlates in various clinical groups over time. One-time “static” snapshots of language behavior so often described in prior language studies are inadequate to capture the dynamic, transactional process of early language development and may yield misleading results (Karmiloff-Smith & Thomas, 2003).

In an intriguing treatise, Karmiloff-Smith (2001) argued that a key to understanding developmental disorders lies in the study of the dynamics of development itself, using a neuroconstructivist approach. Rather than focusing on single behaviors and “unidirectional chains” of single behaviors, she contended that investigators of language development in atypical populations need to evaluate the dynamic interplay among multiple contextual factors (e.g., genetics, brain/behavioral relations, and cognitive, behavioral, and environmental factors) on language and related processes from early infancy onward (see also Cicchetti et al., 1991; Thelen & Bates, 2003). Cicchetti et al. (1991) have further argued that it will be important to assess children's language and communicative competencies in multiple observational contexts that focus on stage-salient developmental issues (i.e., tasks that require the child to coordinate language, cognition, affect, and behavior) and vary in the degree of structure and challenge placed on the child. The overarching promise in such multifactorial longitudinal research is that it will yield detailed, age-specific information on early language and associated processes that will be useful to clinicians, educators, and other professionals in guiding and timing comprehensive intervention and rehabilitation programs for children exhibiting delayed or deviant language development and their families (Bates, 2003).

Genetic Bases of Language Disorders

Inquiry into the genetic bases of language disorders has gained momentum in the past decade, partly in response to the increasing number of behavioral phenotypic studies in different clinical groups, and partly from the hope that further knowledge of the genetic and environmental underpinnings of complex cognitive disorders can lead to more effective diagnoses and therapeutic interventions (Smith & Morris, 2005). In behavioral genetics studies of early language development in typically developing children, results of multivariate genetic modeling revealed a consistently high genetic correlation between vocabulary and grammar at 2 and 3 years, suggesting the same genetic influences operate for both vocabulary and grammar (Dionne, Dale, Boivin, & Plomin, 2003), a finding that is inconsistent with an “autonomy” hypothesis. In addition, results of crosslagged longitudinal genetic models showed that both lexical and syntactic bootstrapping operate from 2 to 3 years. In other behavioral genetics research, a complex interplay between genetic and environmental influences was associated with the timing and process of early language development (Spinath, Price, Dale, & Plomin, 2004), suggesting the need for complex, dynamic systems approaches in future genetic studies of language disorders (Thelen & Bates, 2003).

Two contrasting neurocognitive approaches (“top-down” and “bottom-up”) have recently been described that hold promise for future studies examining genetic contributions to language disorders. Generally speaking, in a top-down approach, the investigator focuses on an “optimal” phenotypic description of language behavior in a genetic disorder and then attempts to understand its genetic and biological underpinnings, often using electrophysiological brain measures (Phillips, 2005). In contrast, in a bottom-up approach, the investigator focuses on primary etiological pathways for language disorders and attempts to explain complex “outcome phenotypes” in terms of more fundamental, underlying difficulties, such as those observed in early-emerging sensorimotor behavior (Muller, 2005).

Both approaches are likely to be valuable, and each has the potential to identify gene effects at various levels of language processing and to describe specific genetic and neurological pathways contributing to language disorders (Rice & Warren, 2005b). For instance, advances in neuroimaging techniques (e.g., event-related potential, functional magnetic resonance imaging [fMRI], and near infrared spectroscopy) during the past 15 years have indicated that neurocortical measures such as these hold great promise for top-down genetic research in developmental language disorders. In studies of typically developing older children and adults, functional neuroimaging data have led to a greater understanding of the ways that dynamic neurocortical systems subserve higher level cognitive processes such as language. Moreover, fMRI studies in older children with specific language impairment or autism have yielded interesting corroborative information regarding behavioral findings in these disorders, with implications for our understanding of brain/behavior relations (Carpenter et al., 2001; Nelson et al., 2002).

However, caution is needed in interpreting findings from this literature, given methodological variations in the use of these techniques across laboratories and related validity and reliability issues (Billingsley-Marshall, Simos, & Papanicolaou, 2004). Further development and refinement of these techniques are needed. A major obstacle for the incorporation of these techniques in research on early language acquisition is that some neuroimaging techniques (e.g, fMRI) cannot be used successfully with infants and young children. This is due to technological limitations regarding movement artifacts, as well as ethical problems associated with sedation (see Nelson et al., 2002; Phillips, 2005, for reviews).

Another methodological obstacle to genetic research in language disorders is that both the top-down and bottom-up methods require accurate, thorough descriptions of language phenotypes (and related cognitive and behavioral processes) in different populations of children with language delays and disorders. Clearly defined phenotypic measures are also necessary to inform and support cellular and molecular studies that will, in turn, lead to the identification of genes that contribute to the complex pathways affect language development and disorders (McCardle et al., 2005).

Unfortunately, precise phenotypic descriptions of many aspects of language and related phenomena do not currently exist (Rice & Warren, 2005b). Part of the problem in coming up with a set of precise, “optimal” measures of language phenotypes in different clinical populations is that investigators from different disciplines have tended to focus on different language phenomena at different ages, with concomitant differences in preferred assessment paradigms and operational definitions of measures. To address and overcome some of these obstacles, Mervis and colleagues (Mervis & Klein-Tasman, 2004; Mervis & Robinson, 2005) have provided several helpful methodological caveats for researchers in this field.

First, the most useful dependent measures of “optimal language phenotypes” (at least in initial studies) are those that assess narrowly defined language behaviors, can be used longitudinally with demonstrated reliability and validity, and can be utilized reliably by different investigators in different laboratories. This is especially important in multisite, cross-population comparative studies. In addition, given the growing cultural diversity in the United States, measures should be selected that recently have been normed (or renormed) for age and gender on geographically and racially representative national samples. Measures that are “culture free” and can be used appropriately in multicultural groups are especially desirable. Moreover, particular phenotypic measures should be selected for genetic evaluation that have known genetically related variation (heritability) in different populations, ideally those that have been shown to be consistent over time and within families, as determined in prior behavioral genetics studies (Mervis & Robinson, 2005).

Second, Mervis and Klein-Tasman (2004) provide caveats pertaining to group-matching designs, which are commonly used to identify diagnosis-specific characteristics of children with language disorders. For instance, they describe the alpha levels needed for control variable comparisons, recommend the use of raw or standard scores rather than age equivalent scores when evaluating group differences on developmental matching variables, and advocate the use of sensitivity and specificity criteria to delineate membership in the target and control groups.

Third, Mervis et al. recommend that investigators eliminate from their study samples (or control for as much as possible) subjects with secondary behavioral or psychiatric conditions (e.g., attention deficit/hyperactivity disorder, depression) or environmental and biological risk factors (e.g., prematurity, prenatal substance exposure, teen parenting) that can co-occur with language disorders and confound interpretation in genotype/phenotype analyses. Assurance that target and comparison groups are matched carefully for gender, race/ethnicity, and sociodemographic characteristics (in addition to developmental features) is also of critical importance.

Fourth and finally, collaborative, multisite cross-population studies of language disorders are encouraged, because they can increase sample size in studies of rare disorders (such as Williams syndrome), overcome problems associated with subject attrition, and make the maximum use of the data. Furthermore, ideal collaborations would be multidisciplinary and incorporate input from scholars in genetics, molecular biology, linguistics, neuroscience, and psychology.

However, cross-site communication in multisite collaborative research is not a simple or easy task. To initiate and maintain effective, successful collaborative research, it will be important to coordinate efforts and methods across multidisciplinary groups prior to start up. As detailed by Mervis and Robinson (2005), key constructs to be measured need to be identified, agreed-upon, and defined, using similar measures, instruments, and assessment paradigms across laboratories. In addition, investigators at different sites should utilize the same design (including specific child ages of assessment and control groups) and statistical analyses, to allow for data archiving and data sharing. Accomplishing these goals will require the implementation of procedures to promote excellent cross-site communication and reliable systems (e.g., a central site) for monitoring quality control at all phases of data collection and reduction.

Individual Differences and the Effects of Biological and Social Risk and Resilience Factors

Within-group variation in language and associated cognitive and behavioral skills is a hallmark feature of many clinical groups of children with delayed or disordered development (Kennedy et al., 1991; Lord et al., 2004; Mervis, 2003; Tager-Flusberg, 2004a; Thal et al., 2004; Tomblin, Zhang, Weiss, Catts, & Weismer, 2004), yet the primary focus in many prior comparative studies has been on describing average group differences in language performance, which can obscure within-group variations. Thus, there is an urgent need for investigators in future translational language research to evaluate individual differences within clinical groups of children with language delays and disorders. This shift in focus will allow for further analysis of data collected in within-group studies and the identification of possible subgroups of children with unique profiles of linguistic, cognitive, and behavioral skills, with implications for both genetic and intervention studies (Lord et al., 2004; Tager-Flusberg, 2004b).

It will also be important in future translational language studies to evaluate the effects of contextual risk and resilience factors that are known to affect variations in language acquisition. Factors such as child gender, temperament, parenting style, and biological and social risk and resilience factors on children's language functioning have been shown to affect children's language performance in both typically developing and various at-risk groups but have been largely ignored in prior research in children with developmental language disorders (Blacher, Kraemer, & Schalow, 2003; Dykens, 2003; Mervis & Robinson, 2005; Torr, 2003). A brief review of this literature is provided here for illustrative purposes.

In typical development, language acquisition usually emerges rapidly and follows a predictable sequence during early childhood. By the end of the preschool period, most typically developing children have mastered the basic components of speech and language development, including a rich, varied lexicon, diversity in semantic and morphosyntactic applications, and pragmatic skills (Berko Gleason, 2005). Moreover, a large body of normative research suggests that there is marked similarity across different ethnic and language groups in the onset and mastery of these skills (Berko Gleason, 2005; Tomasello & Bates, 2001).

However, individual differences in the style and rate of early language acquisition are well documented (Fenson et al., 1994; Shore, 1995). Robust effects of biological and social contextual factors such as child gender, temperament, birthweight premature birth, caregiver interactive style, culture, and demographics on multiple specific aspects of language development have also been reported, which may account for some of this variation (Bates et al., 1994; Goldfield & Snow, 2005; Hart & Risley, 1995; Landry et al., 1997; Massey, 1996; Morisset, Barnard, & Booth, 1995; Spiker et al., 2002).

Caregiving factors are especially critical to consider, as individual differences in early language acquisition have been strongly linked to both distal and proximal measures of the caregiving environment, such as parental education, maternal psychosocial adaptation, and parental interactive style, including the amount and quality of verbal input to the child (Messer, 1994). For instance, low socioeconomic status is often linked with delayed language acquisition. Results of a large, home-based observational study showed that parents from low SES homes spoke significantly less to their young children than parents from middle-class homes (Hart & Risley, 1995), suggesting that the effect of low SES on children's language development is mediated by SES-related variations in parental verbal input to children. In other research, variations in caregiving have been linked to children's language outcomes within low-income samples. For example, in a longitudinal study of African American preschoolers from low-income families, a global measure of maternal responsivity and support in the home environment predicted children's language and early literacy skills (Roberts, Jurgens, & Burchinal, 2005). Similarly, in another longitudinal study of mostly Caucasian low-income toddlers' vocabulary development between 1 and 3 years of age (Pan, Rowe, Singer, & Snow, 2005), maternal lexical input and maternal language and literacy skills exerted positive effects, whereas maternal depression exerted negative effects, on toddlers' lexical outcomes. Moreover, extreme perturbations in the caregiving environment, such as child maltreatment, are strongly associated with delays in children's lexical, syntactic, and pragmatic development during early childhood, even after controlling for general cognitive status (Beeghly & Cicchetti, 1994; Coster, Gersten, Beeghly, & Cicchetti, 1989; Eigsti & Cicchetti, 2004).

At a more proximal level, specific variations in maternal verbal input and sensitivity or responsivity to children during mother–child interaction have been linked with the rate of children's language development, in both typically developing and at-risk groups (Dale, Greenberg, & Crnic, 1987; Dunham & Dunham, 1992). For instance, in multivariate longitudinal studies of children's vocabulary development, Bornstein and colleagues (Bornstein, 1998) showed that mothers' spontaneous expressive vocabulary to their infants uniquely predicted infants' comprehension at 20 months. Effects of variations in the socioaffective quality of parent–infant relationship on language outcomes have also been reported. In a meta-analytic review (van Ijzendoorn, Dijkstra, & Bus, 1995), the quality of attachment between infant and parent was strongly associated with the infant's language development. Similarly, in a study of medically high risk toddlers, additive effects of a secure mother–infant attachment relationship and home stimulation on children's language competence (especially receptive skills) were observed (Murray & Yingling, 2000).

Several investigators have suggested that variations in maternal interactive style and sensitivity may exert stronger effects on early linguistic development when children are at risk for language delay due to the presence of social or biological risk factors (Baumwell, Tamis-LeMonda, & Bornstein, 1997; Beeghly & Cicchetti, 1994). For instance, in Landry's programmatic longitudinal research on prematurely born infants with varying biological risk characteristics, maternal interactive style characterized by a high prevalence of maintaining (rather than redirecting) of the child's focus of attention during dyadic interactive tasks was associated with longitudinal gains in children's language, cognitive, and social functioning in both term and prematurely born children, with larger gains seen in the higher risk preterm groups (see Landry, Miller-Loncar, & Smith, 2002, for a review). Similarly, in a large longitudinal study of the effects of child care on children's outcomes, maternal sensitivity during mother–child interactions from infancy through 36 months mediated the effect of chronic maternal depressive symptoms on children's cognitive and linguistic outcomes (NICHD Early Child Care Research Network, 1999).

Although understudied, similar caregiving effects have been observed in language studies of children with a variety of developmental disabilities. For instance, in experimental intervention studies of children with language delays and with Down syndrome, Yoder, Hooshyar, Klee, and Shaffer (1996) showed that mothers' responsive linguistic behaviors that were fine tuned to their infants' language skills predicted gains in their children's syntactic development. In another study (Yoder & Warren, 1999), maternal verbal responsivity mediated the relationship between children's prelinguistic intentional communication and later language skills. In a study of the early predictors of language in children with and without Down syndrome (Yoder & Warren, 2004), parental verbal responsivity predicted children's later productive language above and beyond etiology. Similarly, in a prospective study of hearing mothers and their deaf and hard-of-hearing children (Pressman, Pipp-Siegel, Yoshinaga-Ito, & Deas, 1999), maternal affective sensitivity to toddlers during mother–child interaction was significantly, positively associated with children's expressive language gain, even after controlling for maternal education, degree of child hearing loss, dyadic mode of communication, and other covariates.

Of course, the direction of effects in these studies is unclear, given that development is dynamic and transactional in nature (Abbeduto & Murphy, 2004; Bates et al., 1982). Parents' psychosocial well-being and interactive style with children are also affected by variations in the child's own developmental and behavioral status. What is still unclear (and deserves further evaluation) is how children's developmental and socioemotional behavioral characteristics affect others' responsivity to them and how this transactional process may indirectly contribute to the quality of child's language-learning environment over time (Abbeduto & Murphy, 2004).

Clinical Implications

Let us now return to the clinician's predicament raised at the beginning of this paper. How can results from longitudinal cross-population research on early language development in at-risk and atypical groups be “translated” into more effective evidence-based clinical practice?

Translational research on early language development has many implications for clinical practice. A few compelling examples are provided here.

First, translational research on atypical language development to date has shown that there are striking individual differences in language acquisition and related cognitive and behavioral processes within different clinical groups and subgroups of children, as well as striking commonalities across conditions. The provision of further detailed information about these cross-population similarities and differences in language profiles and documentation of subtypes within populations would enhance clinicians' ability to identify young children who are likely to develop clinically significant language-learning problems and would enhance clinicians' understanding of the different levels of risk that may predispose very young children for persistent language impairment (Thal et al., 2004). Moreover, this information would help clinicians individualize and customize existing programs and intervention strategies for different children and maximize their effectiveness (Abbeduto & Murphy, 2004).

Second, further longitudinal evaluation of the unique trajectories of language development within and across different clinical groups would shed light on how profiles of abilities within or across clinical groups change or remain the same over time (Lord et al., 2004). This research would also identify the specific contextual factors (biochemical, neurocortical, or environmental) that may be triggering these age-related changes (Rice, 2004). This information would allow clinicians to anticipate accelerations and decelerations in specific skills in different subgroups at different ages, and tailor and fine-tune interventions for individual children at different levels of language functioning in developmentally appropriate ways.

Third, translational research documenting the specific cognitive and behavioral precursors of language development (e.g., joint attention, pretend play) in different clinical groups may assist clinicians in identifying more accurately and at earlier ages children who are at risk for persistent language problems (Yoder & Warren, 2004), which would allow these children to receive intervention services as early as possible. Research suggests that intervention services are most effective when received during infancy and toddlerhood (Guralnick, 1997; Leonard, 1998).

Fourth, the identification of specific biological and social risk factors that may support or derail children's language development in different clinical populations would further assist clinicians in the early identification of children at risk for language problems and offer insights into the most effective interventions. Tomblin, Hardy, and Hein (1991) have suggested that information regarding children's biological and family risk status could help clinicians identify those at greater risk for communicative impairments more clearly. For instance, in their retrospective study of the speech and language status of 662 children between 30 months and 5 years of age, a set of multiple risk factors comprising various family background and birth history variables predicted 55% of children with poor communication skills and 76% of those with normal communicative development (Tomblin et al., 1991).

Regarding the development of effective treatment programs, results from intervention research documenting the efficacy of different types of parental verbal responsivity on children's language outcomes could be incorporated into ongoing parenting programs to maximize their effectiveness (Yoder & Warren, 1999, 2004). More generally, reduction of the overall level of risk for individual children and their families and provision of social support at multiple levels may do much to facilitate positive child developmental outcomes (Dunst, 2000; Tronick & Beeghly, 1999). For instance, results from intervention research spanning nearly three decades (Olds, 2006) have shown that general and specific prenatal and infancy preventive interventions for low-income families provided by home visiting nurses can significantly improve parental care and are associated with better infant and emotional outcomes, particularly for families at greater risk.

Fifth and finally, longitudinal translational research on the efficacy of different intervention programs could provide valuable information to clinicians regarding the relative efficacy of different types of intervention programs on parenting and child language outcomes in different clinical groups, whether these effects vary for children at different ages, and whether different approaches are needed for families from different socioeconomic and cultural backgrounds. Such research could also shed light on how specific intervention parameters (intensity, duration, comprehensiveness of service) may affect parental adaptation, parenting, and children's language outcomes in different clinical groups (see, e.g., Hauser-Cram, Warfield, Shonkoff, & Krauss, 2001; Warfield, Hauser-Cram, Krauss, & Upshur, 2000).