Communicative Cues for Reach-to-Grasp Motions: From Humans to Robots

Intent communication is an important challenge in the context of human-robot interaction. The aim of this work is to identify subtle non-verbal cues that make communication among humans fluent and use them to generate intent expressive robot motion. A human human reach-to-grasp experiment (n = 14) identified two temporal and two spatial cues: (1) relative time to reach maximum hand aperture (MA), (2) overall motion duration (OT), (3) exaggeration in motion (Exg), and (4) change in grasp modality (GM). Results showed there was statistically significant difference in the temporal cues between no-intention and intention conditions. In a follow-up experiment (n = 30), reach-to-grasp motions of a simulated robot containing different cue combinations were shown to the participants. They were asked to guess the target object during robot's motion, based on the assumption that intent expressive motion would result in earlier and more accurate guesses. Results showed that, OT, GM and several cue combinations led to faster and more accurate guesses which imply they can be used to generate communicative motion. However, MA had no effect, and surprisingly Exg had a negative effect on expressiveness.