Dual cognitive task affects reaching and grasping behavior in subjects with macular disorders.

PURPOSE: Subjects with macular disorders need longer time to plan and execute a reaching and grasping task compared with normally sighted controls. In everyday life it is normal to perform reaching and grasping movements while simultaneously carrying out a cognitively demanding task. We investigated whether a simultaneous "counting task" further affects the ability to reach and grasp an object in subjects with visual impairment (VI). As the visually guided action is considered to be solely under the control of the automatic parieto-premotor pathway, we hypothesize that there will be minimal effect of the counting task, needing working memory and attention, which is mediated by other pathways, on the performance of the reaching and grasping tasks.

METHODS

Fourteen subjects with VI and 14 age-matched controls reached out and grasped a target while carrying out a counting task ("easy," "difficult," "no count"). A motion analysis system recorded and reconstructed the 3D hand and finger movements.

RESULTS

Significant differences (P < 0.05) occurred for various indices between the two visual groups. Significant interaction effects occurred between the two groups for "onset time," "time after maximum grip," and "time after maximum velocity," indicating that the dual task affects both the planning of the movement and the ability to carry out "online corrections."

CONCLUSIONS

In both groups, the onset time was affected by the counting task, which requires attention and working memory. In VI subjects, the dual task affected "online corrections," suggesting that visually guided movements are not solely under the control of automatic processes.