DISCUSSION
The current study used a series of object-retrieval tasks of increasing
complexity and varying context to compare the performance of young
children with DS with mental age-matched TD children. Overall, our
results indicated that children with DS were more challenged by the
tasks compared to the mental age-matched TD group. However, the results
were highly task-specific highlighting a strong interaction with the
level of task and contextual complexity. To elaborate, for the easier
task 1 involving retrieving a toy from a transparent box, children with
DS performed similarly to the TD group and did not differ in terms of
overall success and hand use strategies. However, with increasing task
and contextual complexity, children with DS demonstrated specific
difficulties with overall success and performance during the task 2 and
3. For task 2, the DS group had less success, required greater adult
assistance, and longer time to plan the actions compared to the TD
group. For task 3, the DS group showed less use of asymmetric bimanual
strategies and required greater tester assistance compared to the TD
group. Lastly, the DS group took longer to execute the tasks compared to
the TD group. Interestingly, both groups had similar success rate for
task 3 which could be attributed to the floor effects of a complex
object retrieval task involving both task and context complexity.
The motor impairments of children with DS and their impact on object
retrieval was apparent during task 3. Specifically, children with DS
showed limited use of asymmetric bimanual strategies during task 3
compared to the TD group, and no differences for the symmetric bimanual
or unilateral hand use. Bimanual coordination is required for variety of
daily tasks, and evidence from the typical population suggests later
development of asymmetric compared to symmetric bimanual coordination
(Brakke et al., 2007), and its dependence on both the individual and
environmental factors (Kirschner & Tomasello, 2009; Pellegrini et al.,
2004). Additionally, bimanual manipulation is an important achievement
for refining consistent hand preference in children (Nelson, 2022).
Children with DS have poor bilateral coordination compared to
neurotypical children as assessed using standardized motor tests and
motor tasks such as walking (Vali Noghondar et al., 2022; Nocera et al.,
2021; Jobling, 1998). However, there is limited information on the
development and origins of bimanual coordination in infants and young
children with Down Syndrome. More importantly, principles guiding
bimanual training has only been studied in adults with DS, such as
bimanual coordination improves with visual information, stable
handedness, and repeated practice in adults with DS (Ringenbach et al.,
2012; Mulvey et al., 2011; Latash & Patterson, 2002). Future studies
should examine the development of bimanual coordination in infants with
DS along with the impact of individual (e.g., severity of motor,
attentional deficits) and environmental factors (e.g., task difficulty,
visual or auditory stimulus) on performance of infants.
Cognitive impairments, or more specifically differences in executive
skills could also have impacted the overall success rate and task
performance of children with DS. Global differences in executive skills
or its subconstructs such as working memory, cognitive flexibility, and
inhibitory control are commonly reported in children with DS (Tungate &
Conners, 2021; Daunhauer et al., 2014). Similarly, for the study tasks,
children were required to explore multiple strategies, inhibit certain
predominant strategies (such as directly trying to grasp the toy without
opening the lid), and choose the best strategy (such as asymmetric hand
use involving stabilization with one hand and moving with the other
hand). Clearly, children with DS were slower in planning, choosing, and
executing the strategies compared to TD children, but these challenges
became apparent only when the task was complex and/or had additional
contextual complexity of reduced transparency level was added to the
tasks.
The current study also indicated that children with DS required more
time to plan and execute their actions compared to TD children. Slower
movement initiation and execution have been commonly reported in
individuals with DS (Charlton et al., 1996; de Campos et al., 2010;
Kearney & Gentile, 2003; Latash et al., 2002). For example, young
preschoolers with DS (Kearney & Gentile, 2003) as well as school-aged
children with DS (Charlton et al., 1996) had slower speed of reaching
and grasping movements compared to TD controls, along with greater
difficulties in feedback-dependent motor control. However, slowing down
could also be viewed as an adaptive strategy to improve movement
accuracy and performance. Adults with DS were slower than typically
developing adults while tapping a tablet with a stylus but had a similar
accuracy rate of hitting the target (Lam et al., 2009). Furthermore, the
trade-off between the speed of movement and accuracy was a function of
task difficulty (i.e., size and distance). Similar research has not been
done in children with DS, hence, it is unclear whether children with DS
use slowing down as an adaptive strategy to improve task comprehension
and/or performance. Slower processing and execution times could pose
serious challenges on everyday functioning of children and have negative
implications on the learning of new skills and behaviors. Therefore, we
recommend future studies to further investigate slower initiation and
slower movement rate in children with DS, as well as their implications
on everyday functioning and acquisition of new skills.
Lastly, we would like to acknowledge the differences in family
demographics in our study sample. Parental education years were
significantly lower in the DS group compared to the TD group. Several
studies examined the association of socioeconomic status (SES) such as
parents’ education and income with the child’s development including
cognitive and social-emotional development (Bradley & Corwyn, 2002).
Specifically, low maternal/paternal education is associated with poor
academic performance and lower IQ scores in their children, possibly due
to lack of resources, stimulating environment, as well as differences in
parenting styles and attitudes (Mercy & Steelman, 1982; Scarr &
Weinberg, 1978). Research has also demonstrated less effective object
exploration in infants residing in lower SES households compared to
those living in higher-SES households (Tacke et al., 2015). However, if
we follow the cut-offs for low and high SES in the above-mentioned
studies, a majority of the DS families in our study sample could qualify
for high SES. For example, Tacke et al. (2015) considered families with
2+ years of college education as high SES, and 11 out of the total 14 DS
families in our sample had 12+ years of education and would thus fall
under the high SES category (see Table 1 for average parent education
years). We would recommend further investigation of family factors
(e.g., parents’ occupation, education) and neighborhood factors (e.g.,
geographic location) on child’s exploration and manipulation of objects,
especially focusing on intersectional factors that could exist for
children with disabilities living in lower-SES households.