Context dependency in a social rehabilitation scenario Ilaria Bavazzano University of Genoa - DIBRIS IIT - CONTACT Genoa, Italy ilaria.bavazzano@iit.it Carlo Mazzola IIT - RBCS University of Genoa - DIBRIS Genoa, Italy carlo.mazzola@iit.it Giulia Belgiovine IIT - RBCS University of Genoa - DIBRIS Genoa, Italy giulia.belgiovine@iit.it Maura Casadio University of Genoa - DIBRIS Genoa, Italy maura.casadio@unige.it Alessandra Sciutti Italian Institute of Technology (IIT) - CONTACT Genoa, Italy alessandra.sciutti@iit I. INTRODUCTION Human perception works by integrating sensory information with internal models built on previous world experience and acting as priors. This integration is at the basis of Context Dependency, a phenomenon that has already been observed in many perceptual domains, such as visual perception of space [1] and time [2]. It defines the mechanism whereby the perception of a stimulus is affected by the stimuli of the same type perceived before so that their reproduction tends to gravitate toward a mean amplitude. In general, this strategy is adopted to optimize the perceptual error due to the uncertainty of the external world by using priors to reduce the variability of the sensory inputs, even if at the expense of the accuracy. However, in certain cases, the influence of priors can bring a negative outcome. For example, in rehabilitation contexts, subjects should rely less on their internal models, which needs to be corrected to better perceive and reproduce the movements shown by the therapist. Therefore, this research aims firstly to study Context Dependency in the proprioception of the wrist for flexion-extension movements. Furthermore, since [3] demonstrated that during the interaction with a social robot, Context Dependency is less exploited, we will verify whether this variation also occurs for proprioception in the presence of a social robot and improves perceptual performances. II. METHODS AND MATERIALS The experimental task consists of the proprioceptive perception of the wrist in flexion-extension of angular distances shown by the robotic device Wristbot. After a first movement in which participants passively perceived a distance (6°, 9°, 12°, 15°, 18, 21°, 24°), they had to reproduce a movement of equal amplitude for two different sessions. In the individual session, the participant performs the task only with the Wristbot; in the social session, the humanoid robot iCub is present as tutor/therapist during the execution of the task, pretending to control the movement of the Wristbot with a joystick and interacting with the participant. Each session includes 105 trials. Following previous literature, as a measure of Context Dependency, we computed the regression index as the difference in slope between the best linear fit of the reproduced values and the identity line (see fig.1), where 1 indicates a complete regression toward the mean of the stimuli perceived, whereas 0 indicates the absence of Context Dependency. III. PRELIMINARY RESULTS We currently collected preliminary data of the individual session to verify the presence of Context Dependency in proprioception. From a one-tail t-test, we thereby assessed that participants' regression index (7 subj., 2M-5F) was significantly different from 0 (M=0.38 SD=0.15), revealing that they exhibited an evident phenomenon of Context Dependency. IV. CONCLUSIONS Preliminary results revealed for the first time Context Dependency mechanism in proprioception of the wrist. Thus, we can proceed to collect data to verify this phenomenon with larger evidence, which was the first question of this study, and to assess the changes of such a perceptual mechanism during the interaction with the social robot-therapist. Interactions with other agents may have a strong impact with respect to how humans perceive in individual contexts. Investigating these variations may be the chance not only to deepen the basis of social interaction but also to exploit the potential benefits of interacting with others also in the field of rehabilitation. ACKNOWLEDGMENT This work was supported by a Starting Grant from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme. G.A. No 804388, wHiSPER. REFERENCES [1] G. M. Cicchini, R. Arrighi, L. Cecchetti, M. Giusti, and D. C. Burr, “Optimal encoding of interval timing in expert percussionists.,” Journal of Neuroscience, vol. 32, no. 3, pp. 1056–60, Jan. 2012 [2] A. Sciutti, D. Burr, A. Saracco, G. Sandini, and M. Gori, "Development of context dependency in human space perception," Experimental Brain Research, vol. 232, no. 12, pp. 3965–3976, 2014 [3] C. Mazzola, A. M. Aroyo, F. Rea, and A. Sciutti, "Interacting with a social robot affects visual perception of space," Proceedings of 2020 ACM/IEEE International Conference on Human Robot Interaction (HRI'20), pp. 549–557, 2020 Fig.1. A. Data of individual reproduction task B. Experimental set-up