Language and communication development in Down syndrome

Although there is considerable variability, most individuals with Down syndrome have mental retardation and speech and language deficits, particularly in language production and syntax and poor speech intelligibility. This article describes research findings in the language and communication development of individuals with Down syndrome, first briefly describing the physical and cognitive phenotype of Down syndrome, and two communication related domains-hearing and oral motor skills. Next, we describe language development in Down syndrome, focusing on communication behaviors in the prelinguistic period, then the development of language in children and adolescents, and finally language development in adults and the aging period. We describe language development in individuals with Down syndrome across four domains: phonology, semantics, syntax, and pragmatics. Wethen suggest strategies for intervention and directions for research relating to individuals with Down syndrome.     

Speech perception and motor control in children with Down syndrome.

Twelve children with and without Down syndrome (DS) performed eight subtests of an apraxia battery to determine under what conditions children with DS had difficulty performing representational and nonrepresentational gestures. Participants with DS also completed a dichotic listening test. Participants with DS performed just as well as control participants on all aspects of the apraxia battery except a subtest in which they were required to pantomime tool use from verbal instruction. This suggests that children with DS have difficulty generating an action from memory following verbal instruction. Given the sufficient context or visual demonstration, children with DS performed similar to the other participants. As well, there was a great deal of within-group variability for dichotic listening ear advantage. Participants with a greater left ear advantage on the dichotic listening test committed more errors on an imitation test that also included a verbal component than participants with a greater right ear advantage.     

Influence of practice schedules and attention on skill development and retention

Focus of attention during dual-tasks and practice schedules are important components of motor skill performance and learning; often studied in isolation. The current study required participants to complete a simple key-pressing task under a blocked or random practice schedule. To manipulate attention, participants reported their finger position (i.e., skill-focused attention) or the pitch of an auditory tone (i.e., extraneous attention) while performing two variations of a dual-task key-pressing task. Analyses were conducted at baseline, 10 min and 24 h after acquisition. The results revealed that participants in a blocked schedule, extraneous focus condition had significantly faster movement times during retention compared to a blocked schedule, skill focus condition. Furthermore, greatest improvements from baseline to immediate and delayed retention were evident for an extraneous attention compared to the skill-focused attention, regardless of practice schedule. A discussion of the unique benefits an extraneous focus of attention may have on the learning process during dual-task conditions is presented.     

Variability of prior practice in learning and retention of a novel motor response

The schema theory prediction that variability of practice would influence the strength of the motor response schema was investigated. Three groups of subjects, defined by much, little, or no variability of distances moved in prior practice on a linear-slide apparatus, completed 12 initial practice trials. Subjects then had 10 trials to estimate a novel distance from a new starting point. Knowledge of results was provided on the first three trials and withdrawn on the last seven trials. No differences in accuracy of production of the novel distance were noted although evidence for a stronger-schema by the group with little variability was noted on the second transfer trial. On the trials on which knowledge of results was withdrawn this stronger schema group maintained performance while the other two groups showed a decrement in performance.     

Imitation and representational development in young children with Down syndrome

Competence in object search and pretend play are argued to reflect young children's representational abilities and appear delayed in children with Down syndrome relative to social and imitative skills. This paper explores the effects on object search and play of this social strength in children with Down syndrome. Three experiments compared performance on traditional tasks with modified tasks designed to assess the role of imitation in object search and pretend play. Children with Down syndrome, relative to typically‐developing children, were able and willing to imitate hiding actions when no object was hidden (Experiment 1). When imitation was prevented in object search, children with Down syndrome searched less effectively than typically‐developing children (Experiment 2). In play, children with Down syndrome expressed more willingness to imitate a counter‐functional action, modelled by the experimenter, despite apparent competence in spontaneous functional play (Experiment 3). These findings indicate that object search and play behaviours of children with Down syndrome rely more heavily on imitation than is the case for typically‐developing children. The implications for the development of children with Down syndrome and models of representational development are discussed.     

Effects of different attentional strategies and practice on motor efficiency

The effect of different attentional strategies on motor efficiency, measured by reaction-response time components, has historically been based on memory-drum construct theory, which implied limited attention and motor-response processing. The present study contrasts these principles by using a recording system and automatic analysis of reaction-response parameters. A within-subject design allowed detailed observation of the frequency of each preparatory set within each parameter and with control of the effects of practice. Analysis indicates (a) practice changes the effects of the attentional strategies on the components of reaction response but not the actual movement; (b) the motor-set strategy produces shorter movement times and, inversely, higher motor reaction times; and (c) the motor-sensory set integrated strategy produces improvements on each component of the reaction response. These findings suggest the memory-drum construct theory needs revision and should be based on other attentional models.     

The development of route learning in Down syndrome,Williams syndrome and typical development: investigations with virtual environments

The ability to navigate new environments has a significant impact on the daily life and independence of people with learning difficulties. The aims of this study were to investigate the development of route learning in Down syndrome (N = 50), Williams syndrome (N = 19), and typically developing children between 5 and 11 years old (N = 108); to investigate use of landmarks; and to relate cognitive functions to route‐learning ability in these groups. Overall, measures of attention and long‐term memory were strongly associated with route learning, even once non‐verbal ability was controlled for. All of the groups, including 5‐ to 6‐year‐old TD children, demonstrated the ability to make use of all landmark types to aid route learning; those near junctions, those further from junctions, and also distant landmarks (e.g. church spire, radio mast). Individuals with WS performed better than a matched subset of TD children on more difficult routes; we suggest that this is supported by relatively strong visual feature recognition in the disorder. Participants with DS who had relatively high levels of non‐verbal ability performed at a similar level to TD participants.     

Longitudinal assessment of leg motor activity and sleep patterns in infants with and without Down syndrome

Whether infants with Down syndrome (DS) perform leg movements with the same frequency and quality as their typical development (TD) counterparts is equivocal. Furthermore, the relationship between these early leg movements and later onset of locomotor milestones has only been partially explored. The aims of this study were two-fold: (1) to describe the longitudinal leg activity in infants with and without DS (3-6 months), and (2) to examine sleeping patterns and leg activity during the night. In addition, the relationships between leg activities and sleep patterns with locomotor development were explored. An activity monitor was placed monthly on the infant's ankle for 48 h. Data were analyzed to separate day-night, high-low activity, and sleep fragmentation. The results indicate that infants with DS produced more low intensity activity and more fragmented sleep. These findings are discussed in relation to the influence of early motor activity on achievement of functional motor behavior.     

A note on schema and exemplar approaches to motor skill representation in memory

Given the need for a memory representation of well-learned motor skills, a common assumption in motor behavior is that this knowledge is stored in a central, abstracted form. Active production of motor skills has not been used in experimental designs that have provided empirical support for this view of representation, however. Much of the faith in centralized, abstracted forms of memory representation for motor skills is due to the popularity of Schmidt's schema theory, which has adapted the prototype abstraction model from category learning research to the representation of motor skills. Since schema theory was proposed, however, an alternative view that seriously questions the preeminence of the prototype abstraction model for the central representation of knowledge has arisen in the category learning literature. This particular view, termed the specific exemplar model, has led a number of researchers in cognition to develop mixed models that involve both prototypic abstraction and specific exemplar elements. This note, then, identifies what can be perceived as a gap in the empirical knowledge base in motor behavior and discusses the possibility of using the debate about representation for category learning as a stimulus for initiating a similar investigation into the representation of motor skills. A hypothetical specific exemplar model for the memory representation of motor skills is outlined, and possible empirical comparisons between this model and the schema abstraction model are suggested.     

Influence of practice schedule on testing schema theory predictions in adults

Since the publication of Schmidt's (1975) schema theory of motor learning, numerous studies have assessed the variability of practice hypothesis. Of these, only research using children as subjects has provided consistent results. Findings from adult studies have been equivocal. Two experiments were conducted to assess the possibility that the schedule of variable practice during acquisition may be a clue to this equivocality, since only experiments (using adults as subjects) that have provide random variability of practice conditions have consistently supported the tenets of schema theory. Using a two movement rapid timing task, subjects learned to control their actions under one (constant) or four (variable) parameters, with variable practice conducted under either a blocked or a randomized schedule. Results for variable error and absolute constant error showed that random-variable practice provided strong support for the schema theory prediction, whereas blocked-variable practice provided only relatively weak support. Two contrasting implications of these results are discussed with respect to support versus non-support for Schmidt' schema theory.     

Down syndrome and Alzheimer's disease: a link between development and aging

A subset of aged individuals with Down syndrome (DS) exhibits the clinical features of Alzheimer's disease (AD) but our ability to detect dementia in this population is hampered by developmental differences as well as the sensitivity of existing test tools. Despite the apparent clinical heterogeneity in aged individuals with DS, age-associated neuropathology is a consistent feature. This is due to the fact that trisomy 21 leads to a dose-dependent increase in the production of the amyloid precursor protein and subsequently the production of the amyloidogenic fragments leading to early and predominant senile plaque formation. A review of the existing literature indicates that oxidative damage and neuroinflammation may interact to accelerate the disease process particularly in individuals with DS over the age of 40 years. By combining clinical information with measures of brain-region specific neuropathology we can "work backwards" and identify the earliest and most sensitive clinical change that may signal the onset of AD. For the past 50 years, investigators in the fields of mental retardation, developmental disabilities, and aging have been interested in the curious link between AD and DS. The morphologic and biochemical origins of AD are seen in the early years of the lifespan for individuals with DS. Study of the process by which AD evolves in DS affords an opportunity to understand an important link between development and aging. This review will focus on advances in the molecular and clinical basis of this association.     

Changes in step variability of new walkers with typical development and with Down syndrome

Models of human gait are based on adult locomotion. C. E. Bauby and A. D. Kuo (2000) proposed that adults rely on passive mechanisms at the spinal level to control motion in the anteroposterior direction and rely on direct monitoring of postural control in the lateral direction. The authors' purpose in this study was to determine if that model applies to control at the onset of walking in typically developing toddlers (n = 9) and in toddlers with Down syndrome (n = 6). Their longitudinal data suggested that toddlers control gait in a distinctly different manner than adults do. An adult pattern of control emerges with experience. In addition, the effect of experience on the emergence of that pattern is magnified by task-specific early intervention. The present data support the emergence and discovery of efficient patterns of control in this fundamental human behavior.     

Effects of contextual interference and age on acquisition, retention, and transfer of motor skill.

This experiment was designed to investigate the varying conditions of contextual interference within three age groups. 40 5-yr.-olds, 40 7-yr.-olds, and 40 11-yr.-olds practiced the task of throwing beanbags under either low contextual interference (blocked practice), high contextual interference (random practice), or medium contextual interference (combined practice). All subjects performed 30 acquisition trials, 12 retention trials and 6 transfer trials. Analysis indicated that only the 7-yr.-old subjects differed in their performance in the various practice groups. As hypothesized and suggested by developmental theories, the combined and blocked practice groups acquired the task better. On the other hand, the 5- and 11-yr.-olds did not differ in performance in the different practice groups. Whether this is associated with difficulty of the task or the length of practice can be assessed in further study. Contextual interference in different age groups needs further investigation.     

Education and children with Down syndrome: neuroscience, development, and intervention

Of the recent advances in education-related research in Down syndrome, the characterization of the Down syndrome behavioral phenotype has become a potentially critical tool for shaping education and intervention in this population. This article briefly reviews the literature on brain-behavior connections in Down syndrome and identifies aspects of the Down syndrome behavioral phenotype that are potentially relevant to educators. Potential challenges to etiologically informed educational planning are discussed.     

The influence of practice on the development of motor skills in pianists: a longitudinal study in a selected motor task

A longitudinal study was conducted to investigate the influence of practice on the long-term development of expert pianists' motor skills in a relevant musical context. Temporal evenness in standardized scale playing was assessed twice in 19 pianists within an average time interval of 27 months. Questionnaires were used for retrospective assessment of practice quantity and several qualitative parameters related to practicing of scales. The development of temporal evenness in scale playing over the follow-up period correlated with the practice time accumulated during that period and with the average daily practice time. Expert pianists with an average daily practice time of 3.75h or more showed an improvement of performance in this selected motor skill. No significant association was observed between motor skill development during the follow-up period and the content of practice. Stepwise linear regression revealed a model predicting 43% of the variance of motor skill development, with practice time accumulated during the follow-up period as the only predictor. It was concluded that, in expert pianists, maintenance of motor skills in the selected motor task was strongly influenced by practice quantity.     

Effects of iron deficiency in infancy on patterns of motor development over time

This longitudinal study of the effects of iron deficiency in infancy assessed motor development over time in 185 healthy Costa Rican children who varied in iron status at 12-23 months. Longitudinal analyses (hierarchical linear modeling) used the Bayley Psychomotor Index before and both 1 week and 3 months after iron treatment in infancy and the Bruninks-Oseretsky Test of Motor Proficiency - long form at 5 years and short form at 11-14 years. Children with chronic severe iron deficiency in infancy had lower motor scores at the beginning of the study and a lower but parallel trajectory for motor scores through early adolescence. Thus, there was no evidence of catch-up in motor development, despite iron therapy in infancy that corrected iron deficiency anemia in all cases.