Visual and Postural Constraints in Coordinated Movements of the Head in Hand Reaching Tasks

Abstract

The purpose of the present study is to investigate movements of the head spatially and temporally coordinated with hand reach movements simulating industrial assembly tasks. The motions recorded from thirty subjects performing reach movements with the right hand toward eccentric targets indicate that 1) hand movement onset lags head movement onset with a duration proportional to target eccentricity; 2) the head does not aim directly at a target, but travels only a fraction of target eccentricity and often deviates away from the target substantially; and 3) head movements are constrained by the strategy of either controlling the head position in space or controlling head rotation about the torso. These results indicate that head movements are constrained by both visual and non-visual factors. While the major function of the head is to displace the visual gaze toward the target, non-visual constraints, which include postural coordination with whole body movements, also significantly affect head movements.