How Do Task Characteristics Affect the Transitions Between Seated and Standing Reaches?

In 3 experiments, we examined the effects of task characteristics on the selection of a reach action (mode) when several alternatives are afforded. In the bead pickup task, actors had to skewer a 2-mm bead using a sewing needle. Performing this task entailed significant postural control and visual requirements. The block pickup task involved picking up a 3-cm Lego(r) block using a 2-finger grip, which entailed minimal postural and visual demands. In Experiment 1, as reach distance increased, actors performing the bead task consistently changed to reach modes that afforded greater postural stability at closer distances than they did for the block task. Also, during the bead task actors avoided the partial standing reach mode from which it was difficult to maintain the postural control required to complete the bead task. Mode avoidance was not observed for the block task. Experiment 2 showed that actors changed reach modes at distances at which the relative comfort of 2 reach modes changed. The outcome of Experiment 3 indicated that the selection of action mode, including mode avoidance, was associated more closely with the postural demands of the task than visual requirements. The outcome of this investigation indicates that people choose actions that effect the necessary postural control required to complete the task.