Comparable magnitude of haptic size adaptation aftereffects between younger and older people.

Perceptual information is processed independently in each hemisphere at some processing stages. This hemispheric asymmetry is reported to decrease in older people, including for haptic sensation. It has been demonstrated that a prolonged bimanual touch with objects of specific sizes induces a perceptual adaptation aftereffect called haptic size adaptation aftereffect: adaptation to a large/small object in each hand alters the subsequent perceived size of tested objects on the hands as smaller/larger than their actual size. Given that the decrease in hemispheric asymmetry reflects an enhanced inter-hemispheric and inter-hands interaction in older people, an age-related difference in the haptic size adaptation aftereffect could be observed in a bimanual adaptation situation. Our first experiment tested this possibility in the situation where adaptation and test were touched in both hands. We found a comparable magnitude of the aftereffect between younger and older people. In the second experiment, we introduced a situation where adaptation was performed in one hand, and tests were performed with either the adapted or non-adapted hand using a haptic-to-visual size matching task. The aftereffect was only clearly observed for the adapted hand in younger people. However, with some procedural modifications, the third experiment again showed a comparable magnitude of aftereffect between younger and older participants for both two-handed and one-handed adaptations on the adapted hand test in the haptic-to-visual size matching task. Our results suggest that similar perceptual and neural mechanisms, including interhemispheric interactions, underlie haptic size perception in younger and older people.