in turn, strike, receive and give, feed, take an oath, beat a musical rhythm, read for the blind, speak for the mute, reach to a friend, stop a foe." Being able to touch, feel, and manipulate objects in an environment, in addition to seeing (and hearing) them, provides a sense of immersion in the environment that is otherwise not possible. It is quite likely that much greater immersion in a VE can be achieved by the synchronous operation of even a simple haptic interface with a visual and auditory display, than by large improvements in, say, the fidelity of the visual display alone. Real environments or VEs in which one is deprived of the touch and feel of objects seem impoverished, seriously handicap human interaction capabilities, and, at worst, can be disorienting.

Although haptic interfaces are typically designed to be operated by the user's hands, alternative designs suitable for the tactual and motor systems of other body segments are conceivable. However, not all interfaces that interact with the human mechano-sensorimotor systems are haptic interfaces. The distinction is based on the nature of the tasks for which the interface is used. For example, whole body motion interfaces (Chapter 6) concerned with conveying a sense of mobility to the user are not haptic interfaces in a strict sense.

In order to develop cost-effective haptic interfaces, it is necessary to understand the roles played by the mechanical, sensory, motor, and cognitive subsystems of the human haptic system. The mechanical structure of the human hand consists of an intricate arrangement of 19 bones, connected by almost as many frictionless joints and covered by soft tissue and skin. Altogether, the bones are attached to about 20 intrinsic and extrinsic muscles through numerous tendons, which serve to activate 22 degrees of freedom (DOF) of the hand. The sensory system includes large numbers of various classes of receptors and nerve endings in the skin, joints, tendons, and muscles. Appropriate mechanical, thermal, and chemical stimuli activate these receptors, causing them to transmit electrical impulses via the afferent neural network to the central nervous system (of which the brain forms a part), which in turn sends commands through the efferent neurons to the muscles for desired motor action.

Haptic exploration and manipulation of solid objects covers a wide range of haptic functions yet provides a task framework within which the roles of the biomechanical, sensory, motor, and cognitive subsystems can be understood. Exploration is concerned mainly with the extraction of object properties, and it is therefore a sensory dominant task, although

FRONT MATTER (R1-R14)

Executive Summary (1-10)

PART I OVERVIEW (11-88)

PART II RESEARCH AND TECHNOLOGY (89-92)

1 Some Psychological Considerations (93-110)

2 The Visual Channel (111-133)

3 The Auditory Channel (134-160)

4 Haptic Interfaces (161-187)

5 Position Tracking and Mapping (188-204)

6 Whole-Body Motion, Motion Sickness, and Locomotion Interfaces (205-230)

7 Speech, Physiology, and Other Interface Components (231-246)

8 Computer Hardware and Software for the Generation of Virtual Environments (247-303)

9 Telerobotics (304-361)

10 Networking and Communications (362-372)

11 Evaluation of Synthetic Environment Systems (373-378)

PART III APPLICATIONS (379-386)

12 Specific Applications of SE Systems (387-443)

References (444-516)

APPENDIXES (517-518)

A Biographical Sketches (519-525)

B Contributors (526-528)

Index (529-542)