Haptic size aftereffects revisited

Although the existence of haptic size aftereffects has been known for quite some time, e.g. [1, 8, 10, 16], almost all of these studies investigated length and not volume as a measure of size. As the haptic aftereffect of three-dimensional volumes has so far only been observed qualitatively, we investigated the significance of this haptic size aftereffect in more detail by means of a size bisection task. The results are straightforward: after grasping a large sphere for a while, a subsequently grasped smaller test sphere feels even smaller. Likewise, adaptation to a small sphere results in perceiving larger spheres as even larger. The difference in perceived size in these two conditions is on average 24 %. An additional result is that in the haptic size bisection task with spheres as stimuli, participants use volume and not surface area or diameter as a measure of size, as might have been expected on the basis of a haptic volume discrimination task [5].