Touch

Tactile senses, or touch, are an important source of information for animals. Touch provides information when light is unavailable, when noise interference obscures sound, or when vocalizations might attract predators. In mammals, touch is an important aspect of affiliative behaviors in social groups. Touch also provides important information about proximity of food, predators, and other environmental features.

The tactile sense in vertebrates is supported by pressure-responsive nerve cells near the surface of the skin. These act directly as transducers. Tactile receptors are not evenly distributed over the animal's surface. They are in higher concentration, and therefore closer together, on surfaces which are critical for exploration, manipulation, expression, or critical to protect. A standard neurological test in humans involves touching the skin with two needles. On the hands or face, the two stimuli are felt as separate points when only a few millimeters apart. On the upper arm or back, the needles will be felt as a single point when close together and will be felt as separate stimuli only when they have been moved one or two centimeters apart. The upper arm and back are less critical areas and are not involved so much in exploration, manipulation or expression; consequently there are not as many tactile receptors in these areas.

In mammals, such as this domestic dog, Canis familiaris, tactile receptors are associated with hairs on the animal's surface, as well. Specialized long, stiff hairs ("whiskers") enhance the ability of many mammals to assess the location and movement of items near their mouth.

In insects hair-like sensillae play the same role. Again, there are many touch receptors in critical areas, such as the antennae, and many fewer on the thorax and abdomen.