Constraints and principles for the design of human-machine interfaces: a virtual reality approach

We conducted two experiments to compare the visual frames of reference used to scale grasping movements directed at objects with those used to estimate the size of the same objects - either immediately or after a 5-s delay. A virtual "workbench" was employed for presenting two different-sized objects in 3D. Subjects were instructed to pick up or estimate the marked one of the two objects. We found that the presence of the other object affected not only the estimate of the size of the target object when subjects made their estimates both immediately and after a 5-s delay, but also the scaling of grip aperture in flight when subjects picked up the target object after a 5-s delay. However, when subjects picked up the target object immediately, their grasp was scaled to the actual size of the target object and was not influenced by the presence of the other object. These findings suggest that the control of delayed motor actions utilizes the same relative metrics in allocentric frames of reference used by conscious perception, whereas the control of normal visually guided motor actions relies on absolute metrics in egocentric frames of reference. Implications of these findings for the design of human-machine interfaces are discussed.