Neutral Point in Haptic Perception of Softness.

Abstract

Haptic perception of objects‘ softness plays an important role in the identification and interaction with objects. How softness is represented in the brain is yet not clear. Here we investigated whether there is a neutral point in the perceptual representation of haptically perceived softness relative to which the objects are represented as being ”soft” or ”hard”. We created a wide range of softness stimuli, varying from very hard (ceramic) to very soft foam with differently soft foam and silicone stimuli in between. Participants were assigned to one of three different stimulus set conditions: full set (18 stimuli), soft set (13 softest stimuli) or the hard set (13 hardest stimuli). They categorized each stimulus as ”hard” or ”soft” and we estimated the neutral point as the point of subjectively equal categorization as ”hard” or ”soft”. We found that neutral points were different from the middle stimulus of each set. Furthermore, during the course of the experiment neutral points rather moved away from the middle of the stimulus set than towards it. Our results indicate that there might be a neutral point in the representation of haptically perceived softness, however range effects may play a role