This paper presents the foundation for a theory of presence that seeks to answer important questions about telepresence and virtual presence. The theory, which develops the definition of telepresence to include virtual presence as a special case, permits the precise definition of various types and degrees of telepresence. General categories of telepresence are defined, using different types of presence that are proposed in the paper. Three types of specifications are used to make the definitions more precise: (1) a set of tasks, (2) a transformation imposed on the human operator's control output and sensory input, and (3) a transformation of the region of presence. The proposed quantitative measure of telepresence involves both objective and subjective measures. The degree of (objective) telepresence is equal to the probability of successfully completing a specified task. The degree of subjective telepresence is equal to the probability that a human operator perceives that he or she is physically present in a given remote environment. The measure of subjective telepresence involves a psychophysical test and is analyzed using signal detection theory. Real-world complications are addressed and a practical example of a subjective telepresence test is described.

This paper presents the integration of a virtual environment (BlindAid) in an orientation and mobility rehabilitation program as a training aid for people who are blind. BlindAid allows the users to interact with different virtual structures and objects through auditory and haptic feedback. This research explores if and how use of the BlindAid in conjunction with a rehabilitation program can help people who are blind train themselves in familiar and unfamiliar spaces. The study, focused on nine participants who were congenitally, adventitiously, and newly blind, during their orientation and mobility rehabilitation program at the Carroll Center for the Blind (Newton, Massachusetts, USA). The research was implemented using virtual environment (VE) exploration tasks and orientation tasks in virtual environments and real spaces. The methodology encompassed both qualitative and quantitative methods, including interviews, a questionnaire, videotape recording, and user computer logs. The results demonstrated that the BlindAid training gave participants additional time to explore the virtual environment systematically. Secondly, it helped elucidate several issues concerning the potential strengths of the BlindAid system as a training aid for orientation and mobility for both adults and teenagers who are congenitally, adventitiously, and newly blind.

BlindAid is a virtual environment (VE) system that enables blind people to more easily learn about new environments on their own. The system is implemented on a desktop personal computer with a Phantom  haptic interface and three-dimensional spatialized audio. In addition to providing blind users with non-visual stimuli similar to what they will depend on in the actual environment, the system is designed to enhance and accelerate the user's understanding of the unknown environment by giving him/her the ability to interact with the VE in ways that are not possible in the real world. The BlindAid system was developed and evaluated as part of an experimental study related to how people who are blind build cognitive maps of their physical environment and how recent advances in VE technology might support orientation and mobility (O&M) training. The current system is able to provide a visual display and record the user's actions in the VE for later review by researchers and O&M instructors. The paper focuses on the technical development of the system with some results from an initial evaluation by four blind volunteers.

This paper presents a virtual reality system (the BlindAid) developed for orientation and mobility training of people who are newly blind. The BlindAid allows users to interact with different virtual structures and objects via auditory and haptic feedback. This case study aims to examine if and how the BlindAid, in conjunction with a traditional rehabilitation programme, can help people who are newly blind develop new orientation and mobility methods. Follow-up research based on this study, with a large experiment and control group, could contribute to the area of orientation and mobility rehabilitation training for the newly blind. The case study research focused on A., a woman who is newly blind, for 17 virtual sessions spanning ten weeks, during the 12 weeks of her traditional orientation and mobility rehabilitation programme. The research was implemented by using virtual environment (VE) exploration and orientation tasks in VE and physical spaces. The research methodology used both qualitative and quantitative methods, including interviews, questionnaire, videotape recording, and user computer logs. The results of this study helped elucidate several issues concerning the contribution of the BlindAid system to the exploration strategies and learning processes experienced by the participant in her encounters with familiar and unfamiliar physical surroundings. [Box: see text].

When we touch an object, surface loads imposed on the skin are transmitted to thousands of specialized nerve endings (mechanoreceptors) embedded within the skin. These mechanoreceptors transduce the mechanical signals imposed on them into a neural code of the incident stimuli, enabling us to feel the object. To understand the mechanisms of tactile sensation, it is critical to understand the relationship between the applied surface loads, mechanical state at the mechanoreceptor locations, and transduced neural codes. In this paper, we characterize the bulk viscoelastic properties of the primate finger pad and show its relationship to the dynamic firing rate of SA-1 mechanoreceptors. Two threedimensional (3D) finite element viscoelastic models, a homogeneous and a multilayer model, of the primate fingertip are developed and calibrated with data from a series of force responses to micro-indentation experiments on primate finger pads. We test these models for validation by simulating indentation with a line load and comparing surface deflection with data in the literature (Srinivasan, 1989, "Surface Deflection of Primate Fingertip Under Line Load," J. Biomech., 22(4), pp. 343-349). We show that a multilayer model with an elastic epidermis and viscoelastic core predicts both the spatial and temporal biomechanical response of the primate finger pad. Finally, to show the utility of the model, ramp and hold indentation with a flat plate is simulated. The multilayer model predicts the strain energy density at a mechanoreceptor location would decay at the same rate as the average dynamic firing rate of SA-1 mechanoreceptors in response to flat plate indentation (previously observed by Srinivasan and LaMotte, 1991 "Encoding of Shape in the Responses of Cutaneous Mechanoreceptors," Information Processing in the Somatosensory System (Wenner-Gren International Symposium Series), O. Franzen and J. Westman, eds., Macmillan Press, London, UK), suggesting that the rate of adaptation of SA-1 mechanoreceptors is governed by the viscoelastic nature of its surrounding tissue.