then replays it to a stimulator. This stimulator ultimately stimulates a functioning sensory modality. After training, people learn to use the information gained from this stimulation to experience a perception of the sensation they lack instead of the actually stimulated sensation. For example, a leprosy patient, whose perception of peripheral touch was restored, was equipped with a glove containing artificial contact sensors coupled to skin sensory receptors on the forehead (which was stimulated). After training and acclimation, the patient was able to experience data from the glove as if it was originating in the fingertips while ignoring the sensations in the forehead. Tactile systems To understand tactile sensory substitution it is essential to understand some basic physiology of the tactile receptors of the skin. There are five basic types of tactile receptors: Pacinian corpuscle, Meissner's corpuscle, Ruffini endings, Merkel nerve endings, and free nerve endings. These receptors are mainly characterized by which type of stimuli best activates them, and by their rate of adaptation to sustained stimuli. Because of the rapid adaptation of some of these receptors to sustained stimuli, those receptors require rapidly changing tactile stimulation systems in order to be optimally activated. Among all these mechanoreceptors Pacinian corpuscle offers the highest sensitivity to high frequency vibration starting from few 10s of Hz to a few kHz with the help of its specialized mechanotransduction mechanism. There have been two different types of stimulators: electrotactile or vibrotactile. Electrotactile stimulators use direct electrical stimulation of the nerve ending in the skin to initiate the action potentials; the sensation triggered, burn, itch, pain, pressure etc. depends on the stimulating voltage. Vibrotactile stimulators use pressure and the properties of the mechanoreceptors of the skin to initiate action potentials. There are advantages and disadvantages for both these stimulation systems. With the electrotactile stimulating systems a lot of factors affect the sensation triggered: stimulating voltage, current, waveform, electrode size, material, contact force, skin location, thickness and hydration. Electrotactile stimulation may involve the direct stimulation of the nerves (percutaneous), or through the skin (transcutaneous). Percutaneous application causes additional distress to the patient, and is a major disadvantage of this approach. Furthermore, stimulation of the skin without insertion leads to the need for high voltage stimulation because of the high impedance of the dry skin, unless the tongue is used as a receptor, which requires only about 3% as much voltage. This latter technique is undergoing clinical