Touch

In general, VR applications focus on providing visual and auditory feedback and much less on touch or force-feedback. It is easier to develop visual virtual worlds with basic sound effects; it requires less specialized equipment. However, the human haptic system, which involves the tactile and kinesthetic senses, is a very important perception channel. It has been shown that the ability to “touch” virtual objects increases the sense of presence [227].

The term hapticcomes from the Greek word haptesthai, which refers to the sense of touch as the way in which the human body perceives objects and space.

Touch is one of the most important human senses; it can be divided into cutaneous, kinesthetic, and haptic systems. The cutaneous system is composed of mechanoreceptors embedded in the skin. It constitutes the tactile sense, which process any stimulation on the body surface, the skin. The kinesthetic system is composed of receptors located in the muscles, tendons, and joints. It constitutes the kinesthetic sense, which allows us to be aware of our limb positions and movements and muscle tensions. It is also called proprioception, from the Latin proprius, meaning “one's own.”

An example of proprioception is when you touch your nose with closed eyes. To perform such a movement, you rely on the kinesthetic sense to know where your fingertip is relative to your nose. In this and most of the cases, the tactile sense is also involved; the fingertip touches the nose. However, the information that is determinant to the correct execution of the action comes primarily from the kinesthetic sense. Thus, the distinction between tactile and kinesthetic senses is functional and task-dependent [228].