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Modern tools often separate the visual and physical aspects of operation, requiring users to manipulate an instrument while viewing the results indirectly on a display. This can pose usability challenges particularly in applications, such as laparoscopic surgery, that require a high degree of movement precision. Magnification used to augment the view and, theoretically, enable finer movements, may introduce other visual-motor disruptions due to the apparent speed of the visual motion on screen (i.e., motion scaling). In this research, we sought to better understand the effects of visual magnification on human movement performance and control in operating a tool via indirect vision. Ten adult participants manipulated a computer mouse to direct a pointer to targets on a display. Results (Experiment 1) showed that, despite increased motion scaling, magnification of the view on screen enabled higher precision control of the mouse pointer. However, the relative effectiveness of visual magnification ultimately depended on the scale of the physical movement, and more specifically the precision limits of the whole-hand grip afforded by the mouse. When the physical scale of the hand/mouse movement was reduced (Experiment 2), fine-precision control began to reach its limits, even at full magnification. The role of magnification can thus be understood as "amplifying" the particular skill level afforded by the effecting limb. These findings suggest a fruitful area for future research is the optimization of hand-control interfaces of tools to maximize movement precision.

The results suggest that the ageing population (particularly men) may face greater difficulty using an input device such as a mouse that relies on motions of the wrist. In addition, the reduced ROM of the wrist may put the elderly at greater risk of developing cumulative trauma disorders. The implications of these findings for the design of input devices are discussed.

This study examined the impact of target geometry on the trajectories of rapid pointing movements. Participants performed a graphic point-to-point task using a pen on a digitizer tablet with targets and real time trajectories displayed on a computer screen. Circular- and elliptical-shaped targets were used in order to systematically vary the accuracy constraints along two dimensions. Consistent with Fitts' Law, movement time increased as target difficulty increased. Analysis of movement kinematics revealed different patterns for targets constrained by height (H) and width (W). When W was the constraining factor, movements of greater precision were characterized by a lower peak velocity and a longer deceleration phase, with trajectories that were aimed relatively farther away from the center of the target and were more variable across trials. This indicates an emphasis on reactive, sensory-based control. When H was the constraining factor, however, movements of greater precision were characterized by a longer acceleration phase, a lower peak velocity, and a longer deceleration phase. The initial trajectory was aimed closer to the center of the target, and the trajectory path across trials was more constrained. This suggests a greater reliance on both predictive and reactive control.

No abstract