Current state-of-the-art haptic interfaces only provide kinesthetic (force) feedback, yet studies have shown that providing tactile feedback in concert with kinesthetic information can dramatically improve a person's ability to dexterously interact with and explore virtual environments. In this research, tactile feedback was provided by a device, called a contact location display (CLD), which is capable of rendering the center of contact to a user. The chief goal of the present work was to develop algorithms that allow the CLD to be used with polygonal geometric models, and to do this without the resulting contact location feedback being overwhelmed by the perception of polygonal edges and vertices. Two haptic shading algorithms were developed to address this issue and successfully extend the use of the CLD to 2D and 3D polygonal environments. Two experiments were run to evaluate these haptic shading algorithms. The first measured perception thresholds for rendering faceted objects as smooth objects. It was found that the addition of contact location feedback significantly increased user sensitivity to edges and that the use of shading algorithms was able to significantly reduce the number of polygons needed for objects to feel smooth. The second experiment explored the CLD device's ability to facilitate exploration and shape recognition within a 3D environment. While this study provided a validation of our 3D algorithm, as people were able to identify the rendered objects with reasonable accuracy, this study underscored the need for improvements in the CLD device design in order to be effectively used in general 3D environments.

The suggestion that the body surface might be used as an additional means of presenting information to human-machine operators has been around in the literature for nearly 50 years. Although recent technological advances have made the possibility of using the body as a receptive surface much more realistic, the fundamental limitations on the human information processing of tactile stimuli presented across the body surface are, however, still largely unknown. This literature review provides an overview of studies that have attempted to use vibrotactile interfaces to convey information to human operators. The importance of investigating any possible central cognitive limitations (i.e., rather than the peripheral limitations, such as related to sensory masking, that were typically addressed in earlier research) on tactile processing for the most effective design of body interfaces is highlighted. The applicability of the constraints emerging from studies of tactile processing under conditions of unisensory (i.e., purely tactile) stimulus presentation, to more ecologically valid conditions of multisensory stimulation, is also discussed. Finally, the results obtained from recent studies of tactile information processing under conditions of multisensory stimulation are described, and their implications for haptic/tactile interface design elucidated.

This study investigates the effect of update rate on the quality of haptic virtual textures, with the goal to develop a guideline for choosing an optimal update rate for haptic texture rendering. Two metrics, control stability and perceived quality of the virtual haptic texture, were used. For control stability, we examined the effect of update rate on the “buzzing” of virtual haptic textures. For perceived quality, we measured the discriminability of virtual haptic textures rendered at different update rates. Our study indicates that update rates much higher than the conventional 1 kHz are needed in order to achieve a stable rendering of “clean and hard” textured surfaces. We also found that our ability to distinguish textures rendered with different update rates depends on whether the virtual textures contain perceived instability. Based on these results, we provide a general guideline for selecting an optimal update rate for rendering virtual textured surfaces.

This article reports the second study in a series that investigates perceived instability—unrealistic sensations associated with virtual objects—of virtual haptic texture. Our first study quantified the maximum stiffness values under which virtual haptic textures were perceived to be stable (Choi & Tan, 2004). The present study investigated the effect of the collision-detection algorithm by removing the step changes in force magnitude that could have contributed to perceived instability in the first study. Our results demonstrate a significant increase in the maximum stiffness for stable haptic texture rendering. We also report a new type of perceived instability, aliveness, that is characterized by a pulsating sensation. We discuss the possible cause of aliveness and show that it is not always associated with control instability. Our results underscore the important roles played by environment modeling and human haptic perception, as well as control stability, in ensuring a perceptually stable virtual haptic environment.

This paper presents a quantitative characterization of the instability that a human user often experiences while interacting with a virtual textured surface rendered with a force-reflecting haptic interface. First, we quantified the degree of stability/ instability during haptic texture rendering through psychophysical experiments. The stiffness of the virtual textured surface upon detection of instability was measured under a variety of experimental conditions using two texture rendering methods, two exploration modes, and various texture model parameters. We found that the range of stiffness values for stable texture rendering was quite limited. Second, we investigated the attributes of the proximal stimuli experienced by a human hand while exploring the virtual textured surface in an attempt to identify the sources of perceived instability. Position, force, and acceleration were measured and then analyzed in the frequency domain. The results were characterized by sensation levels in terms of spectral intensity in dB relative to the human detection threshold at the same frequency. We found that the spectral bands responsible for texture and instability perception were well separated in frequency such that they excited different mechanoreceptors and were, therefore, perceptually distinctive. Furthermore, we identified the high-frequency dynamics of the device to be a likely source of perceived instability. Our work has implications for displaying textured surfaces through a force feedback device in a virtual environment.