Haptic Force Feedback in Mediated Interaction

In face-to-face communication and collaboration people are used to being able to both see and hear other persons. People also take for granted the possibility to give objects to each other, to shake hands or to get someone’s attention by a pat on the shoulder. However, most systems for mediated collaboration do not take physicality into account. Now emerging media space technologies like threedimensional haptic interfaces makes it possible to interact physically in shared haptic object spaces. Many questions then arise about the effects of these modalities on communication and collaboration. 1 The sense of touch The perception of touch is complicated in nature. The human touch system consists of various skin receptors, receptors connected to muscles and tendons, nerve fibres that transmit the touch signals to the touch centre of the brain, as well as the control system for moving the body. Different receptors are sensitive to different types of stimuli. Tactile perception is defined as perception mediated solely by variations in cutaneous stimulation (Loomis and Lederman, 1986). There are receptors sensitive to pressure, stretch of skin, location, vibration, temperature and pain. Contrary to what one might think, there does not seem to be one receptor type for sensing pressure, another for sensing vibration and so forth. Rather, the different receptors react to more than one stimulus type (Burdea, 1996). The skin on different parts of the body is differentially sensitive to touch. The ability to localise stimulation on the skin depends on the density of the receptors, which are especially dense in the hands and face. Moreover, a great deal of information provided by the kinesthetic system is used for force and motor control. The kinesthetic system enables force control and the control of body postures and motion. The kinesthetic system is closely linked with the proprioceptic system, which gives us the ability to sense the position of our body and limbs. Kinesthetic perception is defined as perception from joints and muscles, by limb movement alone, of hardness, viscosity and shape (Loomis and Lederman, 1986). Receptors (Ruffini and Pacinian corpuscles, and free nerve endings) connected to muscles and tendons provide the positional information. Haptic sensing is defined as the use of motor behaviours in combination with touch to identify objects (Appelle, 1991). In haptic perception both the cutaneous sense and kinesthesis convey significant information about distal objects and events. The haptic system unifies input from many sources, e.g., position of fingers, pressure, into a unitary experience. Manipulation of objects can take many forms and one taxonomy illustrates how diverse functions haptics fulfils in everyday life (Lederman, and Klatzky, 1987). People use different strategies depending on the purpose of the tactile manipulation, such as investigating the weight, form, texture or softness of an object. Joint manipulation of objects can take just as many forms. One example is jointly grasping an object and moving it through an area that might have restrictions (Ruddle et al., 2002). Another example is moving an object by pushing from both sides and lifting the object together. Yet another type of joint manipulation is grasping an object and handing it to another person. In a shared haptic object-space people can coordinate joint movement of objects by signalling direction through haptic force and they can give objects to each other almost without verbal communication. Also, the bilateral (Biggs and Srinivasan, 2002) qualities of haptic perception make it possible to both move an object and to get information from it at the same time. In a collaborative situation these aspects of haptic sensing might facilitate the joint understanding of complex information or how something is constructed 2 Psychology of touch The use of the sense of touch for understanding information in the form of texture and shape is often neglected in computer interface design because of the traditionally perceived dominance of vision for interacting with graphical objects. Touch has by a number of philosophers been seen as dominant over other senses in terms of an existence proof for objects, that is, we test reality of a mirage or illusion by trying to touch it (Heller and Schiff, 1991). Humans tend to think of touch as the “reality sense” because we know that it is relatively easy to fool vision by distorting lenses, differences in lightning and viewing conditions. Traditionally touch has been dismissed as a lower sense whereas vision and hearing are looked upon as the higher senses. Katz (1989) however, argued that touch from a perceptual viewpoint must be given precedence over all other senses because its perceptions have the most compelling character of reality. Katz argued that: “touch plays a far greater role than do the other senses in the development of belief in the reality of the external world. What has been touched is the true reality that leads to perception; no reality pertains to the mirrored image, the mirage that applies itself to the eye.” Other senses are more ambiguous than touch and therefore touch is often used to check on reality. It is hard to imagine that we would believe what we see rather than what we feel. Most people think that an object is rather stable over time