Comparing human reaches across three viewing conditions in a step and reach task

The effects of gaze and step direction on a step and reach task were studied to gain insight to possible motor control strategies used in goal-directed whole-body movements. Head, foot and arm positions were monitored while subjects reached to nine targets in space. In dim light, subjects looked at and reached to actual targets or remembered targets, or reached to remembered targets initially located eccentric to gaze orientation. Final reaching errors were influenced by step and gaze orientations, but gaze direction variables were the largest contributors found to predict reach errors. While spatial memory of target location was initially encoded in eye-centered coordinates, memory of eccentric target location was not updated when subjects stepped and reached. Thus, control strategies were dependent on gaze direction in the dim light conditions.