Haptic Touch Modulates Size Adaptation Aftereffects on the Hand

When we interact with objects using our hands, we derive their size through our skin. Prolonged exposure to an object leads to a perceptual size aftereffect: adapting to a larger/smaller object makes a subsequently perceived object to appear smaller/larger than its actual size. This phenomenon has been described as haptic as tactile sensations with kinesthetic feedback are involved. However, the exact role of different haptic components in generating this aftereffect remains largely underexplored. Here, we investigated how different aspects of haptic touch influence size perception. After adaptation to a large sphere with one hand and a small sphere with the other, participants touched two test spheres of equal or different sizes and judged which one felt larger. Similar haptic size adaption aftereffects were observed (a) when participants repeatedly grasped on and off the adapters, (b) when they simply continued to grasp the adapters without further hand movements, and (c) when the adapters were grasped without involving the fingers. All these conditions produced stronger aftereffects than a condition where the palms were simply resting on the adapter. Our findings suggest that the inclusion of grasp markedly increased the aftereffects, highlighting the pivotal role of haptic interactions in determining perceptual size adaptation. Public Significance StatementProlonged touch of a small or large object can alter how we perceive objects' size that we subsequently touch. This effect allowed us to assess the underlying mechanisms of tactile size perception. We show that not only tactile size itself, but also the manner in which the ball is touched contributes to this effect. These results suggest that the way we interact with objects serve as cues for tactile size perception. Our findings provide insight into the fundamental processes underlying our ability to explore the world using our hands.