An aftereffect is the change in the perception of a (test) stimulus after prolonged stimulation with an (adaptation) stimulus. Usually, this change is in the negative direction, that is, in a direction opposite to that of the adaptation stimulus. Aftereffects are often fast and strong. A well-known example in vision is the waterfall illusion: when looking at trees after staring at a waterfall for a minute or more, the subsequently viewed trees seem to move upwards (Addams, 1834; Swanston and Wade, 1994). Also touch is susceptible to strong aftereffects: temperature, roughness, shape, curvature, motion and size of an object all give rise to aftereffects in touch.