The aim of this study was to determine the extent to which adults with Down syndrome are able to utilise advance information to prepare reach to grasp movements. Ten individuals with Down syndrome, and twelve adult controls, used the right hand to reach out to, and grasp illuminated perspex dowels. Four target dowels were positioned on a table surface, two to each side of the midsaggital plane. In the complete precue condition, participants were provided with information specifying unambiguously the location of the target. In the partial precue condition, participants were given partial advance information, indicating the location of the object relative to the midsaggital plane (left or right). In the null precue condition, advance information concerning the position of the target object was entirely ambiguous. As anticipated, both reaction times and movement times were greater for the participants with Down syndrome than for the controls. The reaction times exhibited by individuals with Down syndrome in the complete precue condition were lower than those observed in the null precue condition (F(1, 18) = 24.2, p < 0.01, f = 0.55), indicating that they had utilised advance information to prepare their movements. When advance information specifying only the location of the target object relative to the midline was provided, reaction times were equivalent to those obtained when ambiguous information was given (F(1, 18) = 0.05, p > 0.20, f = 0.02). In contrast, the control participants exhibited reaction times that were lower in both the complete (F(1, 22) = 11.51, p < 0.01, f = 0.35), and partial precue (F(1, 22) = 3.52, p = 0.07, f = 0.19) conditions, than in the null condition. The movement times exhibited by both groups were not influenced by precue condition. In summary, our findings indicate that individuals with Down syndrome are able to use advance information that specifies precisely the location of the target object, in order to prepare a reach to grasp movement. Partial information that specifies only one dimension of the movement goal (i.e. the position of the object relative to the body midline) is apparently not utilised by these individuals.
Supported by the National Health and Medical Research Council.