Scoping review of the neural evidence on the uncanny valley

The Uncanny Valley (UV) theory predicts that imperfectly human-like artificial agents elicit negative reactions in perceivers. While to date most studies investigating the UV have been behavioral, there is a growing number of neuroscientific studies that hold the potential of shedding light on the automatic processes related to the UV. The current paper provides a scoping review of studies using brain imaging techniques that addressed the UV. Of the total of 74 studies found in the database search, 13 met the inclusion criteria and compared the neural processing of human vs. artificial agent stimuli. Neural differences were found when processing the faces of humans and artificial agents, with reduced responses for the latter in a face-selective brain region, the fusiform face area. At the temporal level, specific event-related potential (ERP) components were susceptible to facial appearance, such as the Late Positive Potential. The studies that employed mentalizing, i.e., reasoning about other agents' behavior, showed that different brain regions of the mentalizing network were engaged, with the temporoparietal junction being more responsive to humans, while the ventromedial prefrontal cortex and the precuneus were more responsive when reasoning about artificial agents. Some commonalities were also observed: the processing of human and artificial agent actions activated comparable brain areas in the sensorimotor cortex. Not only does this scoping review shed light on the neural processes that may underlie the UV, but it also allows for generating predictions with respect to processing differences regarding human and artificial agents.