Memory coding in individuals with Down syndrome

Previous research has identified a deficit in phonological short-term memory in individuals with Down syndrome.

The present work aimed to analyze how a group of 30 individuals with Down syndrome performed in a picture span task compared with 30 typically developing children of the same mental age. The task involved four conditions (i.e., dissimilar, phonologically similar, visually similar, and long-name items) chosen to analyze the strategy used by individuals with Down syndrome to code visually presented nameable items.

Individuals with Down syndrome performed less well than typically developing children. Both groups showed the visual similarity effect.

Taken together, our results confirm that individuals with Down syndrome have a verbal working memory deficit, even when nameable items are presented visually. Mental age appears to be an important determinant of memory coding stage in individuals with Down syndrome.     

Behavioral phenotype of individuals with Down syndrome

Evidence is reviewed for a developmentally-emerging behavioral phenotype in individuals with Down syndrome that includes significant delay in nonverbal cognitive development accompanied by additional, specific deficits in speech, language production, and auditory short-term memory in infancy and childhood, but fewer adaptive behavior problems than individuals with other cognitive disabilities. Evidence of dementia emerges for up to half the individuals studied after age 50. Research issues affecting control group selection in establishing phenotypic characteristics are discussed, as well as the possible genetic mechanisms underlying variation in general cognitive delay, specific language impairment, and adult dementia. MRDD Research Reviews 2000;6:84-95. Wiley-Liss, Inc.     

Reliability of 16 balance tests in individuals with Down syndrome

To assess test-retest reliability scores on 16 balance tests of 21 individuals with Down syndrome whose ages ranged from 5 to 31 yr., participants performed a standing test on firm and soft surfaces with the eyes open and closed, the balance subset of the Bruininks-Oseretsky test, full turn, timed-up-and-go test, forward reach, and sit-to-stand. Each participant completed all 16 tests twice in one day and then again on a subsequent day for a total of 4 sessions. The interclass reliability correlation coefficients (ICC) value for each measure of balance varied considerably by age and sex. Based on having an ICC > .50, only 3 tests were reliable in young males and young females, whereas 5 tests could reliably be used in adult females and 9 tests could reliably be used in adult males. The results of this study raise suspicions as to the reliability of tests commonly used to assess balance and differences in reliability due to age and sex. Results of balance tests should be interpreted with caution in males and females with Down syndrome across the age span.     

An experiment on measuring awareness of stuttering in individuals with Down syndrome

BackgroundAwareness of stuttering is likely to depend upon the development of the metalinguistic skill to discriminate between fluent speech and stuttering and the ability to identify one’s own speech as fluent or stuttered. Presently, little is known about these abilities in individuals with Down syndrome (DS).PurposeThis study investigates whether individuals with DS and typically developing (TD) children who stutter and who do not stutter differ in their ability to discriminate between fluent speech and stuttering. The second purpose of this study is to discover if this ability is correlated with their self-identification ability.MethodAn experiment to investigate awareness with tasks for discrimination of stuttering and self-identification was developed. It was administered to 28 individuals (7–19 years) with DS, 17 of them stutter and 11 do not, and 20 TD children (3–10 years), 8 of them stutter and 12 do not. Skills to discriminate stuttering were compared between these groups and correlated with self-identification within these groups. The influence of stuttering severity and developmental/chronological age on their ability to discriminate was also investigated.ResultsThe ability to discriminate does not differ significantly between the DS and TD group, but is highly influenced by developmental age. This ability correlates with self-identification but only for the TD individuals who speak fluently.ConclusionThe ability to discriminate matures around the age of 7 and conscious awareness may rely on this ability. Differences between the present findings and earlier studies suggest that differentiation in levels and types of awareness is warranted.     

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.     

Hopping skill in individuals with Down syndrome: A qualitative and quantitative assessment

IntroductionIndividuals with Down syndrome (DS) show a delayed acquisition of gross motor skills. Among gross motor skills, hopping is a particular form of jumping that can be performed using one leg. Despite its large use during play and physical activity, this skill in adults with DS has not received much attention so far. Here, we aim at investigating hopping skill in adults with DS both from a quantitative and qualitative point of view.MethodsCenter of mass and dominant leg kinematics during hopping over distance were recorded from 24 adult individuals with DS and from 21 typically developed adults (TD) using two inertial measurement units positioned on the posterior aspect of the lower back and on the lateral malleolus of the hopping leg. From linear acceleration and angular velocity signals, hopping frequency (HF), cycle, stance and flight duration (CD, SD, FD), vertical stiffness (K_V) and peak to peak linear acceleration and angular velocities about the cranio-caudal, antero-posterior and medio-lateral axes were extracted. A qualitative process assessment of the hopping skill was carried out using the performance criteria of the test for gross motor development (TGMD-3). The extracted parameters were submitted to analysis of covariance, with stature as a covariate to rule-out possible confounding effects.ResultsThe qualitative assessment highlighted a poorer hopping performance in the DS group compared to the TD group. DS participants showed higher HF and K_V, shorter CD, SD, FD and lower angular velocity about the cranio-caudal axis compared to the TD group. Significant correlations between the temporal parameters of the quantitative assessment and the results of the qualitative assessment were observed.DiscussionThe poorer motor competence in hopping in individuals with DS compared to TD peers may be related to the shorter flight time and higher vertical stiffness observed in TD peers. The adopted instrumental approach, overcoming the limitations of subjective evaluations, represents a promising opportunity to quantify motor competence in hopping.     

Measurement of range of motion in individuals with mental retardation and with or without Down syndrome

The purpose of this study was to assess differences in variability of three joints' range of motion in the lower extremity among individuals with Down syndrome, mentally retarded individuals without Down syndrome, and sedentary subjects without mental retardation (ns = 13, 25, and 30, respectively). Range of motion for hip and knee flexion was obtained using a Myrin goniometer. For hip abduction the range of motion was obtained using a double protractor goniometer (Brodin type). Three test repetitions were carried out, and the greatest value was recorded. As no significant differences were found between left and right sides for each motion, the average was used to represent the range of motion. The Down syndrome group had significantly higher mean range of motion in hip flexion than the mentally retarded group. No significant differences in mean range of motion were found between Down syndrome and sedentary groups, but a significant difference was observed between the control and mentally retarded groups. In hip abduction, the Down syndrome group showed significantly higher mean range of motion than the control and mentally retarded groups. The control group had significantly a higher mean range of motion than the mentally retarded group. No significant differences were found in knee flexion between the two mentally disabled groups, but significant differences in mean range of motion were found between each of the two groups of mentally retarded individuals and the control group. Because differences exist in mean range of motion between the two mentally disabled groups, individualized and differentiated training programs to improve flexibility must be designed based on the type of handicap.     

Cognitive status in Down syndrome individuals with sleep disordered breathing deficits (SDB)

Twelve subjects with Down syndrome underwent polysomnographic studies during night sleep and performed the Mini-Mental state test and the Raven Progressive Matrices (RPM), sets A, B, and B(1). Sleep-disordered breathing (SDB) deficits were observed in Down syndrome individuals and their Mini-Mental and RPM scores were extremely low. Regression analysis of the results revealed that the number of apneas per hour was related with the results of the RPM, set A, which were also related with the orientation of Mini-Mental test, indicating that the more apneas an individual has the more difficulties he has in the kind of visuoperceptual skills, including orientation, associated with normal right hemisphere functioning, which are tested by set A of the RPM.     

Linguistic profile of individuals with Down syndrome: comparing the linguistic performance of three developmental disorders.

An increasing number of studies, addressing the linguistic abilities of individuals with Down syndrome (DS) suggest that they exhibit strengths and weaknesses within the linguistic domain. This article critically reviews the literature on the linguistic profile of individuals with DS, with particular emphasis on the expression and reception of vocabulary and grammar, including nonverbal linguistic expression during infant development. In doing so, attention is given to recent comparative studies of the linguistic abilities of individuals with DS, Specific Language Impairment (SLI), and Williams syndrome (WS). The possibility that deficits in one cognitive system may have consequences in another cognitive system, and that these consequences may define the nature of the impairment in each clinical syndrome is further discussed with suggestions for future research.     

Preschoolers with Down syndrome do not yet show the learning and memory impairments seen in adults with Down syndrome

Individuals with Down syndrome (DS) exhibit a behavioral phenotype of specific strengths and weaknesses, in addition to a generalized cognitive delay. In particular, adults with DS exhibit specific deficits in learning and memory processes that depend on the hippocampus, and there is some suggestion of impairments on executive function tasks that depend on the prefrontal cortex. While these functions have been investigated in adults with DS, it is largely unclear how these processes develop in young children with DS. Here we tested preschoolers with DS and typically developing children, age‐matched on either receptive language or non‐verbal scores as a proxy for mental age (MA), on a battery of eye‐tracking and behavioral measures that have been shown to depend on the hippocampus or the prefrontal cortex. Preschoolers with DS performed equivalently to MA‐matched controls, suggesting that the disability‐specific memory deficits documented in adults with DS, in addition to a cognitive delay, are not yet evident in preschoolers with DS, and likely emerge progressively with age. Our results reinforce the idea that early childhood may be a critical time frame for targeted early intervention. A video abstract of this article can be viewed at https://www.youtube.com/watch?v=r6GUA6my22Q&list=UU3FIcom6UpITHZOIEa8Onnw     

Nonlinear analysis of the movement variability structure can detect aging-related differences among cognitively healthy individuals

Studying the dynamics of nonlinear systems can provide additional information about the variability structure of the system. Within the current study, we examined the application of regularity and local stability measures to capture motor function alterations due to dual-tasking using a previously validated upper-extremity function (UEF). We targeted young (ages 18 and 30 years) and older adults (65 years or older) with normal cognition based on clinical screening. UEF involved repetitive elbow flexion without counting (ST) and while counting backward by one (DT1) or three (DT3). We measured the regularity (measured by sample entropy (SE)), local stability (measured by the largest Lyapunov exponent (LyE)), as well as conventional peak-dependent variability measures (coefficient of variation of kinematics parameters) to capture motor dynamic alterations due to dual-tasking. Within both groups, only SE showed significant differences between all pairs of UEF condition comparisons, even ST vs DT1 (p = 0.007, effect size = 0.507), for which no peak-dependent parameter showed significant difference. Among all measures, the only parameter that showed a significant difference between young and older adults was LyE (p < 0.001, effect size = 0.453). Current findings highlight the potential of nonlinear analysis to detect aging-related alterations among cognitively healthy participants.     

Changes in the variability of movement trajectories with practice

We studied variability in movement phase plane trajectories (velocity-position relation) during movement. Human subjects performed 10 degrees and 30 degrees elbow flexion and extension movements in a visual step tracking paradigm. The area of ellipses with radii equal to one standard deviation in position and velocity was taken as a measure of trajectory variability. Trajectory variability was determined at 10-ms intervals throughout movements. Trajectory variability in both the acceleration and deceleration phases of movement decreased with practice. The average trajectory variability during deceleration was greater than that during acceleration even after extended practice (1000 trials). During practice, subjects usually increased movement speed while maintaining end-position accuracy. Trajectory variability was also related to movement speed when equal amounts of practice were given. Short duration (fast) movements had greater trajectory variability than long duration movements. Thus there is a tradeoff between movement speed and trajectory variability similar to the classical speed-accuracy tradeoff. Trajectory variability increased rapidly during the acceleratory phase of movement. The rate of increase was positively related to both movement amplitude and speed. Thus, the forces producing limb acceleration were variable and this variability was more marked in faster and larger movements. In contrast, trajectory variability increased more slowly or actually decreased during the deceleratory phase of movements. Forces involved in limb deceleration thus appeared to compensate to a greater or lesser degree for the variability in accelerative forces. The experiments indicate that the entire trajectory of simple limb movements is controlled by the central nervous system. Variations in accelerative forces may be compensated for by associated variations in decelerative forces. The linkage between accelerative and decelerative forces is progressively refined with practice resulting in decreased variability of the movement trajectory.     

Prehension in young children with Down syndrome

Prehension was examined in 3-year old children with Down syndrome (DS, n = 3) and in typically-developing children matched in chronological age (3-year olds; n = 3) or mental age and motor experience (2-year olds; n = 3). The task required reaching to grasp dowels. Video-based movement analysis yielded temporal and kinematic measures. Children with DS were hypothesized to have deficits in feedback-dependent components of prehension (anticipatory grip-closure and deceleration of reach), whereas feedforward components (reach's acceleration phase; grasp's preshaping) were assumed to be unimpaired [Latash, 1993, Control of human movement, pp. 283-292; Latash, 1994, What is clumsiness? In: Motor Control and Down Syndrome II Proceedings of the second international conference, pp. 68-71]. The findings supported these hypotheses. In comparison to control groups, children with DS had significantly: (a) less time in deceleration of reaching, (b) fewer anticipatory grip-closures, and (c) longer movement times for dowel-lift. Young children with DS appeared to use dowel-contact to decelerate the limb and initiate grip-closure. In contrast, reach-acceleration time and grasp-preshaping did not differ across groups. These findings suggest that children with DS display qualitative differences in motor capabilities rather than simply a delayed rate of typical developmental progression.     

At home with Down syndrome and gender

I argue that there is an important analogy between sex selection and selective abortion of fetuses diagnosed with Down syndrome. There are surprising parallels between the social construction of Down syndrome as a disability and the deeply entrenched institutionalization of sexual difference in many societies. Prevailing concepts of gender and mental retardation exert a powerful influence in constructing the sexual identities and life plans of people with Down syndrome, and also affect their families' lives.     

Abstraction of tactile properties by individuals with autism and Down syndrome using a picture‐based communication system

The present study evaluated the efficacy of a set of procedures for bringing tact extensions of abstract tactile properties under stimulus control. Two participants with disabilities who communicated via a picture‐based communication system received reinforcement for tacts of tactile properties of four wet/dry and four hard/soft stimuli. Test trials were conducted to evaluate the extent to which the participants' correct responding generalized to novel stimuli with the same tactile properties. The results suggest that the procedures were effective in bringing tact extensions of abstract tactile properties under stimulus control. Both participants' correct responding generalized to a set of novel stimuli. Mastery level responding to training and test targets maintained for 2 weeks following training. The results provide further evidence supporting the use of DTT to teach stimulus abstraction to nonvocal verbal individuals who use augmentative forms of communication.     

Spatial and temporal limits in cognitive neuroimaging with fMRI

A large body of research in human perception and cognition has been concerned with the segregation of mental events into their presumed hierarchical processing stages, the temporal aspect of such processing being termed ‘mental chronometry’. Advances in single-event functional magnetic resonance imaging (fMRI) have allowed the extraction of relative timing information between the onset of activity in different neural substrates as well as the duration of cognitive processing during a task, offering new opportunities in the study of human perception and cognition. Single-event fMRI studies have also facilitated increased spatial resolution in fMRI, allowing studies of columnar organization in humans. Important processes such as object recognition, binocular vision and other processes are thought to be organized at the columnar level; thus, these advances in the spatial and temporal capabilities of fMRI allow a new generation of cognitive and basic neuroscience studies to be performed, investigating the temporal and spatial relationships between these cortical sub-units. Such experiments bear a closer resemblance to single-unit or evoked-potential studies than to classical static brain activation maps and might serve as a bridge between primate electrophysiology and human studies. These advances are initially demonstrated only in simple visual and motor system tasks and it is likely to be several years before the techniques we describe are robust enough for general use.     

Psychiatric and behavioral disorders in persons with Down syndrome

Similar to the state of the broader intellectual disabilities field, many gaps exist in the research and treatment of mental health concerns in people with Down syndrome. This review summarizes key findings on the type and prevalence of behavior and emotional problems in children, adolescents, and adults with Down syndrome. Such findings include relatively low rates of severe problems in children, and well-documented risks of depression and Alzheimer's disease in older adults. The review also considers emerging data on autism, and the paucity of studies on adolescents. Three next steps for research are highlighted, including a need to: (1) connect research on psychiatric status and diagnoses across developmental periods, including adolescence, and to examine such associated processes as sociability, anxiety and attention; (2) unravel complicated biopsycho-social risk and protective factors that serve to increase or diminish psychopathology; and (3) identify evidence-based treatments that both reduce distressful symptoms and enhance well-being in individuals with Down syndrome.     

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.     

Promoting balance and jumping skills in children with Down syndrome

The purpose of this study was to investigate the changes in balance and qualitative and quantitative jumping performances by 20 children with Down syndrome (3 to 6 years) on jumping lessons. 30 typical children ages 3 to 6 years were recruited as a comparison group. Before the jumping lesson, a pretest was given subjects for balance and jumping skill measures based on the Motor Proficiency and Motor Skill Inventory, respectively. Subjects with Down syndrome received 3 sessions on jumping per week for 6 weeks but not the typical children. Then, a posttest was administered to all subjects. Analysis of covariance showed the pre- and posttest differences on scores for floor walk, beam walk, and horizontal and vertical jumping by subjects with Down syndrome were significantly greater than those for the typical children.     

Play and emotional availability in young children with Down syndrome

This study investigates mother–child interaction and its associations with play in children with Down syndrome (DS). There is consensus that mother–child interaction during play represents an important determinant of typical children's play development. Concerning children with DS, few studies have investigated mother–child interaction in terms of the overall emotional quality of dyadic interaction and its effect on child play. A sample of 28 children with DS (M age = 3 years) took part in this study. In particular, we studied whether the presence of the mother in an interactional context affects the exploratory and symbolic play of children with DS and the interrelation between children's level of play and dyadic emotional availability. Children showed significantly more exploratory play during collaborative play with mothers than during solitary play. However, the maternal effect on child symbolic play was higher in children of highly sensitive mothers relative to children whose mothers showed lower sensitivity, the former displaying more symbolic play than the latter in collaborative play. Results offer some evidence that dyadic emotional availability and child play level are associated in children with DS, consistent with the hypothesis that dyadic interactions based on a healthy level of emotional involvement may lead to enhanced cognitive functioning.