Most decide by "the touch," that is, the feel . . . . --Andrew Ure
Tactile signal. 1. Incoming: A sign received through physical contact with a body part (e.g., a hand or lip), causing it to feel (see HOMUNCULUS). 2. Outgoing: A sign of physical contact (e.g., of pressure, temperature, or vibration) delivered to a body part (see, e.g., KISS).
Usage I: Touch cues are powerful and very real to human beings. If "seeing is believing," then touch is knowing-- i.e., "knowing for sure." Touch cues are used worldwide to show emotion in settings of childcare and courtship, and to establish personal rapport.
Usage II: Touch cues are often used in anxious social settings, e.g., for self-stimulation (see SELF-TOUCH).
Usage III: "Soft" or protopathic touch--found in hairless (or glabrous) areas of the skin--is partly responsible for itching, tickling, and sexual sensations [HB, p. 4-6]. Protopathic touch, which is ancient, gives us little information about the size, shape, texture, or location of a tactile stimulus.
Usage IV. "Itch" sensations may trigger the spinal cord's rhythmic, oscillating scratch reflex. Scratching stimulates pain receptors (nociceptors) which drown out (i.e., block) the itchy feeling. Primates may scratch themselves in anxious social settings.
Usage V. "Tickle" is a tingling sensation, considered both pleasant and unpleasant, which results in laughter, smiling, and involuntary twitching movements of the head, limbs, and torso.
Anatomy. Its outer covering of skin is the body's largest "part." Skin makes up ca. 15% of the body's weight (ca. 23 lbs.), and occupies ca. 21 square feet of surface area [SIG:254]. Pain and protopathic touch cues are received by free nerve endings in the skin and hair follicles. More specialized nerve endings have evolved for finer touch and temperature discrimination. Mechanoreceptors (including Pacinian corpuscles, Merkel's disks, and Meissner's corpuscles) sense pressure, stretching, and indenting of the skin. Thermoreceptors (Krause end bulbs [for cold] and organs of Ruffini [for heat]) are sensitive to changes in temperature.
Evolution. The most primitive, specialized tactile-sense organ of vertebrates is the neuromast, a fluid-filled pit in the skin of fishes which picks up vibration, heat, electrical, and (perhaps) chemical signals in the surrounding water. Each neuromast contains a hair cell, which, when moved by water currents of a nearby fish, e.g., stimulates a sensory nerve. Through the neuromast, the current becomes a nonverbal sign of another fish's presence.
Space. As Apollo 11's pilot, Michael Collins, flew above the Moon, he felt he could "almost reach out and touch it" [L:5].
Neuro-notes: We find pleasure in a carpet's softness, e.g., as it stimulates poorly localized tactile sensations for protopathic touch carried by anterior spinothalamic nerves (whose paleocircuits are phylogenetically older than those for more precise sensations of pain and temperature carried by the lateral spinothalamic nerves; see, e.g., FUR SUBSTITUTE).
See also AROMA CUE, COLOR CUE, EMOTION CUE, TASTE CUE.
Copyright 1998, 1999 (David B. Givens/Center for Nonverbal Studies)
Detail of photo (James Dean holds Julie Harris's hand; copyright by Warner Bros., Inc.)