The Perception of Humans and Robots: Uncanny Hills in Parietal Cortex

The Perception of Humans and Robots: Uncanny Hills in Parietal Cortex Ayse Pinar Saygin (saygin@cogsci.ucsd.edu) Department of Cognitive Science, University of California, San Diego La Jolla, CA 92093-0515 USA Thierry Chaminade (tchamina@gmail.com) Mediterranean Institute for Cognitive Neuroscience, Aix-Marseille University CNRS Marseille, 13402 France Hiroshi Ishiguro (ishiguro@ams.eng.osaka-u.ac.jp) Department of Adaptive Machine Systems, Osaka University Suita, Osaka, Japan Abstract We report on a functional magnetic resonance imaging (fMRI) study of the perception of human and artificial agents. Participants viewed videos of familiar body movements enacted by the android Repliee Q2, the human after whom it was modeled, and the “skinned” version of Q2 revealing its mechanical parts. We used a neural adaptation (repetition suppression) analysis to reveal brain areas sensitive to body movements, and explored whether the identity of the perceived agents modulated these responses. We found significantly higher activity in a distributed network of brain areas for the android, most notably in anterior intraparietal cortex. The responses for the human and the robot with the mechanical appearance resembled each other. We interpret these results within the framework of predictive coding and suggest that the “uncanny valley” phenomenon may have its roots in processing conflicts within the brain’s action perception system. Keywords: action perception; body perception; biological motion; social robotics; artificial agents; neuroimaging; fMRI; uncanny valley Introduction In the near future, artificial agents and humanoid robots are expected to be part of our daily lives, not only in entertainment and retail, but also in important domains such healthcare and education (Billard, Robins, Nadel, & Dautenhahn, 2007; Dautenhahn, 2007; Kanda, Ishiguro, Imai, & Ono, 2004). Thus, exploring human factors in interactive robot design and development is crucial (Ishiguro, 2007; MacDorman & Ishiguro, 2006). Conversely, experiments using artificial agents can address questions about the functional properties of mechanisms involved in the perception of others’ actions (Blake & Shiffrar, 2007; Rizzolatti & Craighero, 2004). Here, we summarize a neuroimaging study that we performed as part of an interdisciplinary research program that aims to reveal factors that can guide the design of future artificial agents, as well as to improve our understanding of action and body movement perception more generally. In primates, the perception of body movements is supported by network of lateral superior temporal, inferior parietal and inferior frontal brain areas (Rizzolatti & Craighero, 2004). Here we will refer to this network as the Action Perception System (APS). The frontal and parietal nodes of the system are known to contain mirror neurons, which respond not only when the monkey executes a particular action, but also when it observes another individual perform the action. The existence of a similar system in humans has been suggested by several neuroimaging and lesion studies (e.g., Fadiga, Fogassi, Pavesi, & Rizzolatti, 1995; Grafton, Arbib, Fadiga, & Rizzolatti, 1996; Hari et al., 1998; Iacoboni et al., 1999; Saygin, 2007; Saygin, Wilson, Dronkers, & Bates, 2004). The neural activity in premotor and parietal regions during action perception is often interpreted within the framework motor resonance, where “an action is understood when its observation causes the motor system of the observer to ‘resonate”’ (Rizzolatti, Fogassi, & Gallese, 2001). But what are the boundary conditions for this resonance? There is a small neuroscience literature on the perception of artificial agents, including robots (Chaminade & Hodgins, 2006; MacDorman & Ishiguro, 2006). Unfortunately, the results are not consistent. Some experiments have reported that robot actions affect the observers’ own motor processing or the activity of the APS, whereas others have argued that the APS does not respond, or responds weakly if the perceived actor is an artificial agent (Catmur, Walsh, & Heyes, 2007; Chaminade, Hodgins, & Kawato, 2007; Gazzola, Rizzolatti, Wicker, & Keysers, 2007; Kilner, Paulignan, & Blakemore, 2003; Oberman, McCleery, Ramachandran, & Pineda, 2007; Press, Gillmeister, & Heyes, 2007; Tai, Scherfler, Brooks, Sawamoto, & Castiello, 2004). Furthermore, the specific roles of biological appearance or biological motion have not been sufficiently explored in these experiments, but is an area of interest in social robotics, cognitive neuroscience, and vision science (Chaminade, Hodgins, & Kawato, 2007; Cook, Saygin, Swain, & Blakemore, 2009; Kanda,