Wearable Haptics for Object Compliance Discrimination through Passive Touch

The ability to estimate compliance is an important human skill related to the tactile sense. When the perception of compliance is mediated by haptic devices, the interaction with objects usually takes place through active exploration from the subject. In this paper, we present a wearable haptic device for transmitting information about object compliance through passive touch, meaning that stimuli are generated by an external agent rather than by user motion. More precisely, the dynamics describing the object indentation is reproduced on the user's forearm in the form of decoupled cues representing applied force and surface displacement. The development of such a device has a twofold purpose. Firstly, it allows the study of the human capacity for processing decoupled information to deduce object compliance. Secondly, it makes possible to convey object compliance to someone who is not performing the object indentation. This is especially important in contexts like telemedicine and human-robot collaboration.Users' perception of stiffness, force, and displacement were estimated. Then, a two-phase experiment was carried out to compare the proposed approach with the state of the art. Results of the experimental campaign revealed the effectiveness of the proposed approach. Users were able to discriminate and order objects with different compliance with a success rate 9% greater than the one obtained exploiting state of the art strategies reproducing only forces.