Weber's Touch Circles

Weber's touch circles, or circles of single sensations, are areas of skin within which two tactile stimuli are perceived as a single sensation; on different areas of the body, these circles have different diameters; the smaller the diameter, the more precisely spatial perception is performed on that area, as two simultaneous touches are distinguished as such at a minimal distance. On the extremities, these circles have an oval shape and are arranged with their long diameter parallel to the axis of the limb. The sizes of Weber's circles (in millimeters): tip of the tongue-1.12, palmar surface of the third phalanx of the fingers--2.25, red part of the lips-4.5, back of the tongue-9, skin of the cheek-11.25, back of the hand-31.5, forearm-40.5, shin-40.5, back (upper part)-53, back of the neck-67.5, back (middle)-67.5, thigh (middle)-67.5. Weber's compass, an instrument for measuring spatial perceptions by the skin; the principle of the device is based on the physiological law according to which two simultaneous touches to the skin at a certain proximity are perceived as one; ,E.