Shape from touch

The shape of objects cannot only be recognized by vision, but also by touch. Vision has the advantage that shapes can be seen at a distance, but touch has the advantage that during exploration many additional object properties become available, such as temperature (Jones, 2009), texture (Bensmaia, 2009), and weight (Jones, 1986). Moreover, also the invisible backside of the objects can provide shape information (Newell et al., 2001). In active touch, both the cuteanous sense (input from skin receptors) and the kinesthetic sense (input from receptors located in muscles, tendons, and joints) play a role. For such active tactual perception, the term “haptic perception” is used (Loomis and Lederman, 1986). Typical exploratory movements to determine shape by touch are “enclosure” for global shape and size, and “contour following” for exact shape (Lederman and Klatzky, 1987; Klatzky and Reed, 2009). By means of touch, both three-dimensional and two-dimensional shapes can be recognized, although the latter is much harder.