The uncanny valley effect is a hypothesized psychological and aesthetic relation between an object's degree of resemblance to a human being and the emotional response to the object. The uncanny valley hypothesis predicts that an entity appearing almost human will elicit uncanny or eerie feelings in viewers.
Examples of the phenomenon exist among robots, animatronics, and lifelike dolls as well as visuals produced by 3D computer animation and predominantly by artificial intelligence. The increasing prevalence of digital technologies (e.g., virtual reality, augmented reality, and photorealistic computer animation) and their increasing verisimilitude have prompted debate about "the valley".
Etymology As related to robotics engineering, robotics professor Masahiro Mori first introduced the concept in 1970 from his book titled , phrasing it as . Bukimi no tani was translated literally as uncanny valley in the 1978 book Robots: Fact, Fiction, and Prediction written by Jasia Reichardt. Over time, this translation created an unintended association 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 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 becomes almost human, at which point the response quickly becomes strong revulsion. However, as the robot's appearance continues to become less distinguishable from that of 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 steep decrease followed by a steep increase (hence the "valley" part of the name) in the areas where anthropomorphism is closest to reality.
This interval of repulsive response aroused by a robot with appearance and motion between a "somewhat human" and "fully human" entity is the uncanny valley effect. The name represents 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.
Theoretical basis
A number of theories have been proposed to explain the cognitive mechanism causing the phenomenon, though support for each is inconsistent: Feature atypicality/anomaly recognition: When an entity possesses some feature or aspect that appears unexpected or otherwise violates one's prediction of how such a feature should appear on that entity. This idea has strong underpinnings in predictability. Consider violation of human norms: If an entity looks sufficiently nonhuman, its human characteristics are noticeable, generating empathy. However, if the entity looks almost human, it elicits our model of a human other and its detailed normative expectations. The nonhuman characteristics are noticeable, giving the human viewer a sense of strangeness. In other words, a robot which has an appearance in the uncanny valley range is not judged as a robot doing a passable job at pretending to be human, but instead as an abnormal human doing a bad job at seeming like a normal person. This idea is often best captured by noticing that the uncanny valley is elicited when something which looks mechanical moves human-like, or, the converse, something which looks human moves mechanically. This has been associated with perceptual uncertainty and the theory of predictive coding. Category error: Varying degrees of ambiguity may sometimes qualify an entity as not easily understood or determined. In such cases, a person's sorting or categorizing of an entity may be delayed or inaccurate. This idea is also referred to as category failure, category conflict, or categorization difficulty. Subtly, but importantly, this concept is sometimes labeled category confusion, but research support for this term is less strong. This could be an extension of the concept of Sorites paradoxes: stimuli with human and nonhuman traits undermine our sense of human identity by linking qualitatively different categories, human and nonhuman, by a quantitative metric: degree of human likeness.Ramey, 2005. The following point elucidates the idea of category error. Conflicting perceptual cues: The negative effect associated with uncanny stimuli is produced by the activation of conflicting cognitive representations. Perceptual tension occurs when an individual perceives conflicting cues to category membership, such as when a humanoid figure moves like a robot or has other visible robot features. This cognitive conflict is experienced as psychological discomfort (i.e., "eeriness"), much like the discomfort that is experienced with cognitive dissonance. Several studies support this possibility. Mathur and Reichling found that the time subjects took to gauge a robot face's human- or mechanical-resemblance peaked for faces deepest in the uncanny valley, suggesting that perceptually classifying these faces as "human" or "robot" posed a greater cognitive challenge. However, they found that while perceptual confusion coincided with the uncanny valley, it did not mediate the effect of the uncanny valley on subjects' social and emotional reactions—suggesting that perceptual confusion may not be the mechanism behind the uncanny valley effect. Burleigh and colleagues demonstrated that faces at the midpoint between human and non-human stimuli produced a level of reported eeriness that diverged from an otherwise linear model relating human-likeness to affect. Yamada et al. found that cognitive difficulty was associated with negative affect at the midpoint of a morphed continuum (e.g., a series of stimuli morphing between a cartoon dog and a real dog). Ferrey et al. demonstrated that the midpoint between images on a continuum anchored by two stimulus categories produced a maximum of negative affect, and found this with both human and non-human entities. Schoenherr and Burleigh provide examples from history and culture that evidence an aversion to hybrid entities, such as the aversion to genetically modified organisms ("Frankenfoods"). Finally, Moore developed a Bayesian mathematical model (founded on categorical perception) that provides a quantitative account of perceptual conflict. There has been some debate as to the precise mechanisms that are responsible. It has been argued that the effect is driven by categorization difficulty, configural processing, perceptual mismatch, frequency-based sensitization, and inhibitory devaluation. Mortality salience: Viewing an "uncanny" robot elicits an innate fear of death and culturally supported defenses for coping with death's inevitability.... disassembled androids...play on subconscious fears of reduction, replacement, and annihilation: (1) A mechanism with a human façade and a mechanical interior plays on our subconscious fear that we are all just soulless machines. (2) Androids in various states of mutilation, decapitation, or disassembly are reminiscent of a battlefield after a conflict and, as such, serve as a reminder of our mortality. (3) Since most androids are copies of actual people, they are doppelgängers and may elicit a fear of being replaced, on the job, in a relationship, and so on. (4) The jerkiness of an android's movements could be unsettling because it elicits a fear of losing bodily control. Mate selection: Automatic, stimulus-driven appraisals of uncanny stimuli elicit aversion by activating an evolved cognitive mechanism for the avoidance of selecting mates with low fertility, poor hormonal health, or ineffective immune systems based on visible features of the face and body that are predictive of those traits.Rhodes, G. & Zebrowitz, L. A. (eds) (2002). Facial Attractiveness: Evolutionary, Cognitive, and Social Perspectives, Ablex Publishing. Pathogen avoidance: Uncanny stimuli may activate a cognitive mechanism that originally evolved to motivate the avoidance of potential sources of pathogens by eliciting a disgust response. "The more human an organism looks, the stronger the aversion to its defects, because (1) defects indicate disease, (2) more human-looking organisms are more closely related to human beings genetically, and (3) the probability of contracting disease-causing bacteria, viruses, and other parasites increases with genetic similarity." The visual anomalies of androids, robots, and other animated human characters cause reactions of alarm and revulsion, similar to corpses and visibly diseased individuals. Threat to humans' distinctiveness and identity: Negative reactions toward very humanlike robots can be related to the challenge that this kind of robot leads to the categorical human–non-human distinction. Kaplan stated that these new machines challenge human uniqueness, pushing for a redefinition of humanness. Ferrari, Paladino and Jetten found that the increase of anthropomorphic appearance of a robot leads to an enhancement of threat to the human distinctiveness and identity. The more a robot resembles a real person, the more it represents a challenge to our social identity as human beings. Religious definition of human identity: The existence of artificial but humanlike entities is viewed by some as a threat to the concept of human identity. An example can be found in the theoretical framework of psychiatrist Irvin Yalom. Yalom explains that humans construct psychological defenses to avoid existential anxiety stemming from death. One of these defenses is 'specialness', the irrational belief that aging and death as central premises of life apply to all others but oneself.Yalom, Irvin D. (1980) "Existential Psychotherapy", Basic Books, Inc., Publishers, New York The experience of the very humanlike "living" robot can be so rich and compelling that it challenges humans' notions of "specialness" and existential defenses, eliciting existential anxiety. In folklore, the creation of human-like, but soulless, beings is often shown to be unwise, as with the golem in Judaism, whose lack of human empathy and spirit can lead to disaster, however good the intentions of its creator. Uncanny valley of the mind or AI: Due to rapid advancements in the areas of artificial intelligence and affective computing, cognitive scientists have also suggested the possibility of an "uncanny valley of mind". Accordingly, people might experience strong feelings of aversion if they encounter highly advanced, emotion-sensitive technology. Among the possible explanations for this phenomenon, both a perceived loss of human uniqueness and expectations of immediate physical harm, are discussed by contemporary research.
Research
A series of studies experimentally investigated whether uncanny valley effects exist for static images of robot faces. Mathur MB & Reichling DB used two complementary sets of stimuli spanning the range from very mechanical to very human-like: first, a sample of 80 objectively chosen robot face images from Internet searches, and second, a morphometrically and graphically controlled 6-face series set of faces. They asked subjects to explicitly rate the likability of each face. To measure trust toward each face, subjects completed an investment game to measure indirectly how much money they were willing to "wager" on a robot's trustworthiness. Both stimulus sets showed a robust uncanny valley effect on explicitly rated likability and a more context-dependent uncanny valley on implicitly rated trust. Their exploratory analysis of one proposed mechanism for the uncanny valley, perceptual confusion at a category boundary, found that category confusion occurs in the uncanny valley but does not mediate the effect on social and emotional responses.