Prior static visual information on material properties increases the efficiency of a subsequent haptic exploration

Previous studies have demonstrated how humans use distinct exploratory procedures (EPs) in active touch that are specialized for materials with particular properties: e.g., rubbing for coarse textures, rotating movements for granular materials, or pressing for highly deformable objects. Research also suggests that humans derive high-level expectations on such dominant mechanical material properties from visual images (Wijntes et al., 2019). Here we investigate whether similar visual stimulus information guides haptic exploration by supporting the selection of named specialized haptic exploratory procedures. For that, we conducted a virtual reality-supported experiment combined with video recording of hand movements and real-world haptic stimuli differing in their dominant material property. In each trial, participants haptically explored two stimuli which were both either of the material type sandpaper, silicone, or sand and had to decide which one is rougher, more deformable or more fine-grained, respectively. In half of the trials, visual information on the dominant material property of the upcoming stimuli was presented in the virtual scene. Visual information disappeared automatically when participants started reaching towards the stimuli. Movement recordings were manually decoded with regard to the EP type at initial contact, the onset times of those EPs that are specialized for the respective material, and the exploration time of the first stimulus. Results show an increase and earlier onsets of the appropriate specialized EPs at initial contact and reduced overall exploration time when prior visual information on the material type was given. We conclude that static visual information on material properties increases the efficiency of a subsequent haptic exploration with regard to movement selection.