On Feeling and Reaching: Touch, Action, and Body Space

One of the most important functions of an organism is the ability to move around the environment and to interact with objects within the environment. Spatial information is crucial here. For example, we need to know where objects are on a cluttered table in order to be able to move toward and grasp that ubiquitous cup of coffee while avoiding spilling the jug of juice. Importantly, we need to know where these items are with respect to our own body in order to perform these movements accurately. This requires spatial information about our own body parts, from proprioception and touch as well as visual information about the items in the environment. In turn somatosensory input is not just used for guiding actions, but can also directly provide spatial perceptual information about the environment through haptic exploration, as well as about our targets on our own body. These spatial somatosensory perceptual experiences are not necessarily veridical, but can be prone to specific distortions. In healthy participants, distortions in somatosensory experience may tell us something about the underlying spatial representations. However, perceptual somatosensory experience can also be disturbed in clinical populations. In this chapter I start by providing an overview of the functional organization of the somatosensory system. Somatosensory input is important for providing a representation of our body as well as for haptic exploration of external objects. Both are reviewed next. A representation of the space surrounding our body, the peripersonal space, has been linked to body representations as well as goal-directed action and is described next. Finally, spatial processes underlying the guidance of reaching and grasping are discussed.