Haptic environments are user interfaces incorporating a haptic display device, most commonly a point force device such as the PHANToM. Lederman and Klatzky’s Exploratory Procedures work casts doubt on the usability of such devices, as the human haptic system can only perform rapidly and accurately when full hand contact is used rather than a single finger. However, this work has not been extended to virtual ob- jects displayed by point force devices. Usability of multisensory interfaces is even more complex. How does the addition of a force display change performance in a graphical system?

This dissertation presents two benchmark tasks for human performance with point force displays. Stimuli were generated using Koenderink’s shape and curvedness scales for smooth quadric surfaces. The first task, psychophysical magnitude estimation of curvature of paraboloid stimuli, was used to analyze the contribution of haptics to a predominantly visual task. Estimates using vision alone made slightly better discrim- inations than estimates using both senses, although the effect only approached significance. The second task extended Lederman and Klatzky’s shape recognition work to point force environments. Participants learned to haptically recognize 5 shapes from the shape scale and then identified random instances of those shapes. Despite the simplicity of the shapes, the median time was 23 s and median accuracy 87%. Adding a visual cursor did not appreciably change performance.

These results are comparable to physical shape recognition with a single finger, so the benchmarks are useful metrics of haptic environment performance. They indicate that point force haptic performance is considerably worse than full-hand haptics. The results also indicate that point force haptic perception and vision are not simply additive. The addition of haptics to the first task interfered with performance, while the addition of graphics to the second task had little effect. The poor performance of point force haptics may be due to its unfamiliarity. The experience of point force haptics appears to be sufficiently different from physical haptics that we cannot presume a simple equivalence between display technology and human senses. Users require practice to interpret both the force display and the visual display of the force location.