The Uncanny Valley: Existence and Explanations

More than 40 years ago, Japanese roboticist Masahiro Mori (1970/2005) proposed the "uncanny valley" hypothesis, which predicted a nonlinear relation between robots' perceived human likeness and their likability. Although some studies have corroborated this hypothesis and proposed explanations for its existence, the evidence on both fronts has been mixed and open to debate. We first review the literature to ascertain whether the uncanny valley exists. We then try to explain the uncanny phenomenon by reviewing hypotheses derived from diverse theoretical and methodological perspectives within psychology and allied fields, including evolutionary, social, cognitive, and psychodynamic approaches. Next, we provide an evaluation and critique of these studies by focusing on their methodological limitations, leading us to question the accepted definition of the uncanny valley. We examine the definitions of human likeness and likability, and propose a statistical test to preliminarily quantify their nonlinear relation. We argue that the uncanny valley hypothesis is ultimately an engineering problem that bears on the possibility of building androids that may some day become indistinguishable from humans. In closing, we propose a dehumanization hypothesis to explain the uncanny phenomenon.