Visual feedback about one’s own movements can be important for effective performance in natural and computer-generated environments. Previous work suggested that, for young adults, performance in virtual environments was influenced by the presence of a crude representation of the hand in a task-specific fashion. The current study was performed to determine whether this pattern of results holds across the lifespan. Specifically, we were interested in determining whether a representation of the hand is useful for movement performance in children, middle adults, and older adults when they reach to grasp an object, transfer it between their two hands, or receive it from a partner. Surprisingly, visual feedback condition had very little effect on performance in the current experiment, with the exception that participants in all three age groups altered how wide they opened their hand when grasping depending on visual condition. Patterns of reach and grasp performance changed across task depending on age, with older adults displaying different patterns than children and middle-aged adults. These results suggest that feedforward planning and the use of feedback are modulated by both age and task.

This work explores how people use visual feedback when performing simple reach-to-grasp movements in a tabletop virtual environment. In particular we investigated whether visual feedback is required for the entire reach or whether minimal feedback can be effectively used. Twelve participants performed reach-to-grasp movements toward targets at two locations. Visual feedback about the index finger and thumb was provided in four conditions: vision available throughout the movement, vision available up to peak wrist velocity, vision available until movement initiation, or vision absent throughout the movement. It was hypothesized that vision available until movement onset would be an advantage over a no vision situation yet not attain the performance observed when vision was available up to peak velocity. Results indicated that movement time was longest in the no vision condition but similar for the three conditions where vision was available. However, deceleration time and peak aperture measures suggest grasping is more difficult when vision is not available for at least the first third of the movement. These results suggest that designers of virtual environments can manipulate the availability of visual feedback of one's hand without compromising interactivity. This may be applied, for example, when detailed rendering of other aspects of the environmental layout is more important, when motion lag is a problem or when hand/object concealment is an issue.

In this series of experiments, we investigated whether a crude representation of the hand that was extinguished at movement onset improved performance when compared to a no-feedback situation. Subjects performed simple reach to grasp movements in a virtual environment in two experiments. In Experiment 1, trials were blocked so that subjects were aware that a graphical representation of the hand would either be available throughout the movement (FA), be removed at movement onset (FAB), or not be available (NF). In Experiment 2, trials were randomized so that subjects were unaware of whether feedback would be available throughout the trial or removed at movement onset. Our results indicated that when subjects were aware of the availability of graphical feedback, the FAB condition improved performance compared to the NF condition. Furthermore, movement time was similar in the two feedback available conditions (FA, FAB). In contrast, for the randomized trial presentation, the positive influence of the FAB condition was diminished. These results suggest that visual feedback available prior to movement onset can be used to calibrate the proprioceptive system and improve performance over a no feedback situation. These results can be applied by designers of virtual environments to solve problems related to occlusion of important environmental information by the hand as users reach to grasp and manipulate objects.

This work explores how the availability of visual and haptic feedback affects and kinematics of reaching performance in a tabletop virtual environment. Eight subjects performed reach-to-grasp movements toward target objects of various sites in conitions where visual and haptic feedback were either present or absent. It was found that movement time was slower when visual feedback of the moving limb was not available. Further MT varied systematically with target size when haptic feedback was available (i.e. augmented targets), and thus followed Fitts' law. However, movement times were constant regardless of target size when haptic feedback was removed. In depth analysis of the reaching kinematics revealed that subjects spent longer decelerating toward smaller targets in conditions where haptic feedback was available. In contrast, deceleration time was constant when haptic feedback was absent. These results suggest that visual feedback about the moving limb and veridical haptic feedback about object contract are extremely important for humans to effectively work in virtual environments.