Sequential aiming movements and the one-target advantage in individuals with Down syndrome.
Clients with Down syndrome can plan movement sequences just like peers, so slow performance means give more thinking time, not simpler tasks.
01Research in Context
What this study did
Researchers asked 24 adults with Down syndrome to tap two targets in a row.
They compared speed and accuracy to adults without disabilities.
The goal was to see if planning two moves at once is harder for Down syndrome.
What they found
Both groups moved faster when aiming at just one target.
This "one-target advantage" was the same size for both groups.
The delay comes from the brain's timing, not weak muscles.
How this fits with other research
Katz et al. (2003) saw the same pattern in toddlers. Kids with Down syndrome kept trying on hard puzzles as long as mental-age peers.
Durbin et al. (2019) looked at sleep learning. They found Down syndrome kids did NOT improve a block-building task after a nap, while typical kids did.
Saville et al. (2002) tested word memory. Like our motor task, the bottleneck was in the mind, not the mouth.
Why it matters
When you teach a client with Down syndrome a chained task like hand-washing, give extra time between steps. The arms can do the work; the brain just needs a moment to queue the next move.
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02At a glance
03Original abstract
Research has revealed that individuals with Down syndrome (DS) have elevated reaction times, longer movement times, and greater movement errors during single-target single-limb actions compared to their typically developing (TD) peers. These perceptual-motor impairments have been attributed to both central processes and the physical phenotype associated with DS. The purpose of the present study was to directly investigate these possible central and peripheral deficits by examining how individuals with DS plan and execute more complex movements. Three groups (DS, TD, and individuals with an undifferentiated intellectual disability; UID) of 8 participants completed a single target movement, a two-target movement performed by a single arm, and a two-target movement where the first movement was performed with one arm and the second movement performed with the other arm. For all groups and all conditions, movement times revealed a one-target advantage (OTA). Specifically, times to the first target were longer in the two-target responses compared to the single-target response. In general, the OTA finding reveals that persons with DS utilise planning strategies similar to their TD peers when performing sequential actions involving two targets and two arms. Furthermore, because the OTA was observed in both the single- and two-arm two-target responses the interference in movement one associated with having to make a subsequent movement is not due to peripheral processes associated with single limb constraints. Rather, individuals with DS treat movements within a sequence as functionally dependent. Thus, the central processes associated with timing the implementation of the second element of the movement appear to be responsible for the interference that leads to the OTA.
Research in developmental disabilities, 2013 · doi:10.1016/j.ridd.2013.08.006