  Social touch provides a rich non-verbal communication channel between humans
and robots. Prior work has identified a set of touch gestures for human-robot
interaction and described them with natural language labels (e.g., stroking,
patting). Yet, no data exists on the semantic relationships between the touch
gestures in users' minds. To endow robots with touch intelligence, we
investigated how people perceive the similarities of social touch labels from
the literature. In an online study, 45 participants grouped 36 social touch
labels based on their perceived similarities and annotated their groupings with
descriptive names. We derived quantitative similarities of the gestures from
these groupings and analyzed the similarities using hierarchical clustering.
The analysis resulted in 9 clusters of touch gestures formed around the social,
emotional, and contact characteristics of the gestures. We discuss the
implications of our results for designing and evaluating touch sensing and
interactions with social robots.
