WPI HIVE: Haptic Senses Page

Human Interaction in Virtual Environments Lab
Department of Computer Science
Worcester Polytechnic Institute

Touch: Elements of the Haptic Senses

The sense of touch is arguably the most complex. This is partially due to several types of sensations all being attributed to this single "sense." Broadly speaking, our sense of touch can be divided into kinesthetic and cutaneous sub-senses. Kinesthetic stimulation maps roughly to forces being exerted on, and sensed by, mechanoreceptors in the joints, tendons, and muscles. For example, we feel the weight of a heavy object held in an upturned palm because the object weight exerts forces on the wrist, elbow, and shoulder joints, and we exert opposite forces to counter the weight. Proprioception, knowing where your limbs are without looking at them, is another example of a kinesthetic sense. Cutaneous stimuli, in contrast, are sensed through mechanoreceptors in the skin layers. There are several kinds of receptors, each allowing us to sense a different type of stimulus, such as thermal properties, vibration of varying frequencies, pressure, and pain. The sense of balance is also sometimes included as a cutaneous sense. The sense of touch is the only one where the entire system conducts both sensing and actuation, e.g., our hands are used both to sense the temperature of a stove, and to move away in case it is hot.

The technologies for generating force-feedback (kinesthetic) stimuli are typically cumbersome, have limited range of motion, and are designed for special purpose applications. On the other hand, these devices can typically generate strong forces and arrest user motion in a realistic manner. Tactile (cutaneous) devices typically generate weaker forces than force-feedback devices. As with sound, a tactile stimulus is made up of a signal with varying frequency and amplitude. Much work has focused on the use of pin arrays for stimulating one of the most sensitive parts of the body, the distal finger pad of the index finger. More-recent work has focused on the use of large numbers of inexpensive vibrating DC motors distributed over a larger area of the body. These devices cannot arrest the motion of the user, but can provide a means for displaying contact cues, as well as other types of information.

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