Psychophysical evaluation of haptic perception under augmentation by a handheld device.

OBJECTIVE: This study investigated the effectiveness of force augmentation in haptic perception tasks. BACKGROUND: Considerable engineering effort has been devoted to developing force augmented reality (AR) systems to assist users in delicate procedures like microsurgery. In contrast, far less has been done to characterize the behavioral outcomes of these systems, and no research has systematically examined the impact of sensory and perceptual processes on force augmentation effectiveness. METHOD: Using a handheld force magnifier as an exemplar haptic AR, we conducted three experiments to characterize its utility in the perception of force and stiffness. Experiments 1 and 2 measured, respectively, the user's ability to detect and differentiate weak force (<0.5 N) with or without the assistance of the device and compared it to direct perception. Experiment 3 examined the perception of stiffness through the force augmentation. RESULTS: The user's ability to detect and differentiate small forces was significantly improved by augmentation at both threshold and suprathreshold levels. The augmentation also enhanced stiffness perception. However, although perception of augmented forces matches that of the physical equivalent for weak forces, it falls off with increasing intensity. CONCLUSION: The loss in the effectiveness reflects the nature of sensory and perceptual processing. Such perceptual limitations should be taken into consideration in the design and development of haptic AR systems to maximize utility. APPLICATION: The findings provide useful information for building effective haptic AR systems, particularly for use in microsurgery.

A model of motor performance during surface penetration: from physics to voluntary control.

The act of puncturing a surface with a hand-held tool is a ubiquitous but complex motor behavior that requires precise force control to avoid potentially severe consequences. We present a detailed model of puncture over a time course of approximately 1,000 ms, which is fit to kinematic data from individual punctures, obtained via a simulation with high-fidelity force feedback. The model describes puncture as proceeding from purely physically determined interactions between the surface and tool, through decline of force due to biomechanical viscosity, to cortically mediated voluntary control. When fit to the data, it yields parameters for the inertial mass of the tool/person coupling, time characteristic of force decline, onset of active braking, stopping time and distance, and late oscillatory behavior, all of which the analysis relates to physical variables manipulated in the simulation. While the present data characterize distinct phases of motor performance in a group of healthy young adults, the approach could potentially be extended to quantify the performance of individuals from other populations, e.g., with sensory-motor impairments. Applications to surgical force control devices are also considered.