A special sense is a sense that has a specific organ devoted to the purpose of receiving the sensory input that leads to perception. Vision, for example, is a special sense because the eyes are specifically devoted to receiving light input which is converted into understandable visual information in the brain. Touch, the primary general sense, does not have a devoted sensory organ but instead interprets a variety of sensory signals through receptors inside and outside of the body. One of the major distinctions between the general and special senses is the mechanism through which the sensory data is communicated to the central nervous system.
Each special sense has a dedicated nervous system pathway that communicates the relevant sensory information to the central nervous system. The special somatic afferents (SSAs) are those nerves that are dedicated to the specialized senses of vision, hearing, and balance. Specifically, the optic nerve is responsible for the specialized sense of vision while the vestibulocochlear nerve is responsible for hearing and balance. The special visceral afferents (SVAs) are responsible for carrying sensory data regarding taste and smell. The special afferent nerves specifically related to taste and smell are the olfactory, facial, glossopharyngeal, and vagus nerves.
The general sense of touch, which includes the perception of pressure, vibration, pain, heat, and relative location of the various parts of the body, is governed by the somatosensory system. As opposed to the specific nervous pathway that would handle a specialized sense, these various forms of touch are processed by a vast system of receptors and nervous pathways throughout the body. These receptors are highly prevalent within the skin and are also found within muscles, joints, bones, various internal organs, and many other locations. The sense of touch is perceived and processed by a wide variety of organs and nervous pathways and is not tied to a single sensory organ, marking it as a general rather than special sense.
The special sense organs tend to form during the early stages of embryonic development, but the full development of some of these sense organs takes years. Human eyes, for instance, continue to grow and develop for roughly the first eight years of a child's life. Additionally, newborns tend to be able to respond only reflexively to sounds, though the capacity for more complex sound comprehension develops quickly. The specialized sense of taste, on the other hand, is at its most acute at birth but tends to diminish later in one's life. This is also true of smell.
