Chih-Hao Ho

An experimental study on the role of touch in shared virtual environments

Investigating virtual environments has become an increasingly interesting research topic for engineers, computer and cognitive scientists, and psychologists. Although there have been several recent studies focused on the development of multimodal virtual environments (VEs) to study human-machine interactions, less attention has been paid to human-human and human-machine interactions in shared virtual environments (SVEs), and to our knowledge, no attention paid at all to what extent the addition of haptic communication between people would contribute to the shared experience. We have developed a multimodal shared virtual environment and performed a set of experiments with human subjects to study the role of haptic feedback in collaborative tasks and whether haptic communication through force feedback can facilitate a sense of being and collaborating with a remote partner. The study concerns a scenario where two participants at remote sites must cooperate to perform a joint task in an SVE. The goals of the study are (1) to assess the impact of force feedback on task performance, (2) to better understand the role of haptic communication in human-human interactions, (3) to study the impact of touch on the subjective sense of collaborating with a human as reported by the participants based on what they could see and feel, and (4) to investigate if gender, personality, or emotional experiences of users can affect haptic communication in SVEs. The outcomes of this research can have a powerful impact on the development of next-generation human-computer interfaces and network protocols that integrate touch and force feedback technology into the internet, development of protocols and techniques for collaborative teleoperation such as hazardous material removal, space station.

Virtual environments for medical training: graphical and haptic simulation of laparoscopic common bile duct exploration

We develop a computer-based training system to simulate laparoscopic procedures in virtual environments for medical training. The major hardware components of our system include a computer monitor to display visual interactions between 3D virtual models of organs and instruments together with a pair of force feedback devices interfaced with laparoscopic instruments to simulate haptic interactions. We simulate a surgical procedure that involves inserting a catheter into the cystic duct using a pair of laparoscopic forceps. This procedure is performed during laparoscopic cholecystectomy to search for gallstones in the common bile duct. Using the proposed system, the user can be trained to grasp and insert a flexible and freely moving catheter into the deformable cystic duct in virtual environments. The associated deformations are displayed on the computer screen and the reaction forces are fed back to the user through the force feedback devices. A hybrid modeling approach was developed to simulate the real-time visual and haptic interactions that take place between the forceps and the catheter, as well as the duct; and between the catheter and the duct.

Efficient Point-Based Rendering Techniques for Haptic Display of Virtual Objects

Computer haptics, an emerging field of research that is analogous to computer graphics, is concerned with the generation and rendering of haptic virtual objects. In this paper, we propose an efficient haptic rendering method for displaying the feel of 3-D polyhedral objects in virtual environments (VEs). Using this method and a haptic interface device, the users can manually explore and feel the shape and surface details of virtual objects. The main component of our rendering method is the neighborhood watch algorithm that takes advantage of precomputed connectivity information for detecting collisions between the end effector of a force-reflecting robot and polyhedral objects in VEs. We use a hierarchical database, multithreading techniques, and efficient search procedures to reduce the computational time such that the haptic servo rate after the first contact is essentially independent of the number of polygons that represent the object. We also propose efficient methods for displaying surface properties of objects such as haptic texture and friction. Our haptic-texturing techniques and friction model can add surface details onto convex or concave 3-D polygonal surfaces. These haptic-rendering techniques can be extended to display dynamics of rigid and deformable objects.

Ray-Based Haptic Rendering: Force and Torque Interactions between a Line Probe and 3D Objects in Virtual Environments

Virtual environments (VEs) that enable the user to touch, feel, and manipulate virtual objects through haptic interactions are expected to have applications in many areas such as medicine, CAD/CAM, entertainment, fine arts, and education. The current state of technology allows the human operator to interact with virtual objects through the probe (such as a thimble or a stylus) of a force-reflecting haptic interface. Most of the current haptic interaction algorithms model the probe as a single point and allow the user to feel the forces that arise from point interactions with virtual objects. In this paper, we propose a ray-based haptic-rendering algorithm that enables the user to touch and feel convex polyhedral objects with a line segment model of the probe. The ray-based haptic-rendering algorithm computes both forces and torques due to collisions of the tip and/or side of the probe with multiple virtual objects, as required in simulating many tool-handling applications. Since the real-time simulation of haptic interactions between a 3D tool and objects is computationally quite expensive, the ray-based rendering can be considered as an intermediate step toward achieving this goal by simplifying the computational model of the tool. To compare the ray- and point-based haptic interaction techniques in the haptic perception of 3D objects, we conducted perceptual experiments in which the participants were asked to identify the shape of four different 3D primitives (sphere, cone, cylinder, and cube) that were displayed in random order using both point-and ray-based techniques. The results of the study show that on average, 3D objects are recognized faster with ray-based rendering than with point-based rendering.

Haptic Interactions in the Real and Virtual Worlds

In humans or machines, haptics refers to the use of hands for manual sensing and manipulation. Recently, haptic machines that enable the user to touch, feel, and manipulate virtual environments have generated considerable excitement. Synthesizing virtual haptic objects requires an optimal balance between the human haptic ability to sense object properties, computational complexity to render them in real time, and fidelity of the device in delivering the computed mechanical signals. In this paper, we primarily describe the progress made in our “MIT Touch Lab” over the past few years concerning the development of haptic machines, the paradigms and algorithms used in the emerging field of “Computer Haptics” (analogous to Computer Graphics), and experimental results on human perception and performance in multimodal virtual environments. Several ongoing applications such as the development of a surgical simulator and virtual environments shared by multiple users are also described.