In aesthetics, the is a hypothesized relation between an object's degree of resemblance to a human being and the emotional response to the object. The concept suggests that humanoid objects that imperfectly resemble actual human beings provoke uncanny or strangely familiar feelings of uneasiness and revulsion in observers. "Valley" denotes a dip in the human observer's affinity for the replica—a valence that otherwise increases with the replica's human likeness.
Examples of the phenomenon exist among robotics, 3D computer animations and lifelike dolls. The rising prevalence of technologies (e.g., virtual reality, augmented reality, and photorealistic computer animation) has propagated discussions and citations of the "valley"; such conversation has enhanced the construct's verisimilitude. The uncanny valley hypothesis predicts that an entity appearing almost human will risk eliciting cold, eerie feelings in viewers.
Etymology
Robotics professor Masahiro Mori first introduced the concept in 1970 from his book titled , phrasing it as . Bukimi no tani was literally translated as uncanny valley in the 1978 book Robots: Fact, Fiction, and Prediction written by Jasia Reichardt. Over time, this translation created an unintended link of the concept to Ernst Jentsch's psychoanalytic concept of the uncanny established in his 1906 essay On the Psychology of the Uncanny (), which was then famously critiqued and extended in Sigmund Freud's 1919 essay The Uncanny ().
Hypothesis
Mori's original hypothesis states that as the appearance of a robot is made more human, some observers' emotional response to the robot becomes increasingly positive and empathetic, until it reaches a point beyond which the response quickly becomes strong revulsion. However, as the robot's appearance continues to become less distinguishable from a human being, the emotional response becomes positive once again and approaches human-to-human empathy levels. When plotted on a graph, the reactions are indicated by a deep trough (hence the "valley" part of the name) in the areas where anthropomorphism is closest to reality.
This area of repulsive response aroused by a robot with appearance and motion between a "somewhat human" and "fully human" entity is the uncanny valley. The name captures the idea that an almost human-looking robot seems overly "strange" to some human beings, produces a feeling of uncanniness, and thus fails to evoke the empathic response required for productive human–robot interaction.