Human processing of social versus object-based touch and its implications for robotics

Although progress in social robotics has been considerable, human-robot interaction is largely limited to visual and verbal processing, with the use of touch in robots largely focused on object manipulation. Although humans use such object-based touch, another crucial aspect of touch is social, e.g. when hugging a person or tapping their shoulders to get attention. Here, we investigated differences between object-based and social touch using behavioural and brain imaging experiments. We used a novel database of 75 videos, displaying both social (e.g., hugging a person) and object-based touch scenarios (e.g. carrying a box). Importantly, low-level aspects of the videos (type of grasp and motion energy) were matched between the two categories. In the behavioural task, 22 participants evaluated pleasantness and arousal of the videos. Subsequently, fMRI brain-scans were made to investigate brain activity during passive touch observation. Our behavioural results showed that social touch spanned the range of positive-negative and high-low arousing ratings, whereas object-based touch was perceived as neutral and un-arousing. Similarly, brain imaging results revealed wide-spread differences in both sensory and higher-level brain areas. These results show the importance of going “beyond objects”, giving robots the ability to interpret (and execute) social touch events for richer human-robot interaction.status: publishe