The Role of Visual and Manual Demand in Movement and Posture Organization

The organization of upper body and gaze movements was quantified as an attempt to identify the types of task descriptors associated with the visual and manual functions of movement control. Nine subjects were asked to either read a word (high visual demand), reach a target (low visual demand), or simultaneously read a word and reach the object target placed just below the word (high visual demand). Similarly the manual demand condition was either low or high, depending on the target distance from the shoulder (either 80 or 120% of extended arm length, respectively). Torso flexion and gaze-on-target duration showed that movements are influenced by the both visual and manual demands in an interactive manner. Also both torso posture and gaze movements were predominantly changed by the visual demand. These results suggest that tasks to be simulated should be described in terms of both visual and manual demand.