The World of Touch

Despite its behavioural significance and omnipresence throughout the animal kingdom, the sense of touch is still one of the least studied and understood modalities. There are multiple forms of touch, and the mechanosensory basis underlying touch perception must be divided into several distinct sub-modalities (such as vibration or pressure), as will be made clear by the contributions elsewhere in this encyclopaedia. The commonality of all touch sensing systems is that touch experience is mediated by specialised receptors embedded in the integument—the outer protective layers of the animal such as the mammalian skin or the arthropod cuticle. Comparative research on touch, and its neuroethology, is only just beginning to provide a larger picture of the different forms of touch sensing within the animal kingdom. We begin our volume by reviewing works on several different invertebrate and vertebrate species, focusing on mechanosensation, each one with a specific requirement for tactile information. The aim of this introductory overview is to give selected examples of research on important model organisms from various classes of the animal kingdom, ranging from the skin of worms to the feelers of insects, and from the whiskers of a rat to the human hand. We conclude by discussing forms of human touch and the possibility of its future extension via synthetic systems.