To date, most human-computer interactive systems have focused primarily on the graphical rendering of visual information and, to a lesser extent, on the display of auditory information. Among all senses, the human haptic system provides unique and bidirectional communication between humans and their physical environment. Extending the frontier of human-machine interaction, haptic interfaces—or force feedback devices—have the potential to increase the quality and capability of human-computer interaction by exploiting our sense of touch and ability to skillfully manipulate objects. The direct physical interaction with computer-generated objects enabled by haptic interfaces provides a useful and intuitive augmentation to visual display and the opportunity to enhance the understanding of, and interaction with, complex data sets. Several novel applications already effectively use haptic technologies; these include molecular docking, nanomaterial manipulation, surgical training, virtual prototyping, and digital sculpting.

Compared to visual and auditory display, haptic rendering has extremely demanding computational requirements. To maintain a stable system while displaying smooth and realistic forces and torques, haptic update rates of 1 kHz or more are typical. Haptics presents new challenges in the development of novel data structures to encode shape and material properties, as well as new techniques for data processing, analysis, physical modeling, and visualization. This special issue examines some of the latest advances on haptic rendering and applications, and provides an introductory view of the challenges and opportunities in the field.

The first article, a tutorial by Salisbury, Barbagli, and Conti, provides an overview of the haptics field with a particular focus on the architecture of haptic rendering systems and the devices that enable force feedback-based haptic interaction. Unlike graphic and auditory rendering, the rendering of haptic interactions requires modeling the physical interactions between objects and generating forces that arise during contact and motion in real time. As in the field of computer graphics, practitioners of computer haptics are intensely interested in the best rendering methods of objects, so that humans can meaningfully perceive them. This topic alone is a vast area that will occupy researchers for years to come. The first article gives a basic view of methods used to render the way an object feels—it discusses modeling these physical interactions and the dynamic stability issues that arise in real-world implementations.

In the design of haptic systems, we need to consider the sensory, perceptual, and cognitive abilities and limitations of humans. In the second article, Hale and Stanney present a review of physiological and psychophysical aspects of human cutaneous and kinesthetic senses, followed by a discussion of issues related to incorporating haptic interaction with a graphical display. The authors present several design guidelines for developing multimodal interaction systems. Their objectives were to identify conditions under which haptic interaction might enhance human perception and performance. By combining neurological and behavioral research methods, they evaluate various sensory integration methods (for example, ramp-up patterns or timing) for better design of haptic interaction systems.

A key area in haptics receiving increased attention is the rendering of surface texture. Surface texture typically refers to microgeometric features on object surfaces in haptic rendering. Intrinsic surface properties like textures are among the most salient haptic characteristics of objects. The third article by Choi and Tan presents a survey on systematic studies of issues that contribute to the perceived instability of haptic texture rendering. The authors conduct psychophysical experiments to investigate conditions under which perceived instability of virtual texture occurs and the type of perceived instability frequently reported by users. By analyzing the measured data, they identify the proximal stimuli that caused the perceived instability and indicate the sources that produce the stimuli.

The next article by Mahvash and Hayward describes an efficient method to synthesize the nonlinear haptic response of deformable models from prerecorded simulation. This article defines high-fidelity haptic synthesis. It then characterizes force response due to deformation in terms of deflection—that is, the displacement of the initial point of contact between an instrument and a deformable body. Therefore, the full specification of the mutual response between a pair of soft objects can be described by force fields for each pair of surface points. By taking advantages of off-line computation, various effects of contact mechanics can be reproduced accurately at the desired haptic update rates by online interpolation among a finite set of precalculated (or premeasured) force fields. This approach is useful for modeling soft objects in virtual environments and is important for developing surgical simulators with high-fidelity force feedback.

Some of the most exciting applications of force feedback have been found in surgical simulation. Research includes simulation for a variety of medical procedures, for example, limb surgery, eye surgery, plastic surgery, gastrointestinal endoscopy, epidural anesthesiology, and laparoscopic procedures. Among them, haptics plays a key role in training both sensorimotor and cognitive skills required for surgery. The article by Muniyandi et al. presents an overview of research on distributed, collaborative haptic systems for laparoscopic surgery. It also describes several key technologies—such as ray-based collision detection and a force model—in the design of haptic rendering systems for medical training.

Concluding this issue is an article by Kim et al. presenting a haptic rendering technique based on a hybrid surface representation—a combination of a geometric and an implicit surface model. This representation addresses many limitations in haptic displays and achieves fast, accurate, and stable simulation of surface properties including friction, stiffness, and textures. Based on the hybrid representation, the authors present techniques for decorating and editing a model using a haptic interface. Their prototype sculpting system allows the user to paint directly on the 3D model and edit local surface properties. This representation can be potentially applied to various applications, such as digital art and medical training.

As this issue examines some of the recent developments in haptic rendering and applications, we believe that computational haptics—a human interface technology still in its early stages—will significantly improve and enrich human-computer interaction by engaging one of our most basic sensory channels: the sense of touch.

We thank all the authors and anonymous reviewers who contributed to this special issue. We are also grateful to the staff of IEEE CG&A for their support and assistance in reviewing, formatting, and finalizing the details for this special issue.

Ming Lin is an associate professor in the Department of Computer Science at the University of North Carolina (UNC), Chapel Hill. Her research interests include haptics, physically based modeling, robotics, and geometric computing. Lin received a BS, MS, and PhD in electrical engineering and computer science from the University of California, Berkeley. She received the National Science Foundation Young Faculty Career Award in 1995, the Honda Research Initiation Award in 1997, the UNC/IBM Junior Faculty Development Award in 1999, and the UNC Hettleman Award for Scholarly Achievements in 2002. She has served as a program committee member for many leading conferences on virtual reality, computer graphics, robotics, and computational geometry. She also serves on the steering committee of ACM Siggraph/Eurographics Symposium on Computer Animation. She is an associate and guest editor of several journals and magazines.

Kenneth Salisbury is a member of the faculty at Stanford University in the departments of Computer Science and Surgery. His research interests include robotics, haptics, human—machine interaction, collaborative computer-mediated haptics, and surgical simulation. Salisbury received a PhD in mechanical engineering from Stanford University. Among the projects with which he has been associated are the Stanford-JPL Robot Hand, the JPL Force-Reflecting Hand Controller, the MIT Whole Arm Manipulator, and the Black Falcon Surgical Robot. His work with haptic interface technology led to the founding of SensAble Technologies, producers of the Phantom haptic interface and FreeForm software. He was a scientific adviser to Intuitive Surgical, where his efforts focused on the developing dexterity-enhancing telerobotic systems for surgeons. He has served on the National Science Foundation's Advisory Council for Robotics and Human Augmentation, as scientific adviser to Intuitive Surgical, and as technical adviser to Robotic Ventures.