The Tipping Point of Animacy

Imagining Others' Minds: The Positive Relation Between Children's Role Play and Anthropomorphism

Children’s role playing, whether personifying toys or imagining invisible friends, involves imagining others’ minds and internal states. Similarly, anthropomorphism – the attribution of internal states to non-human others (e.g., animals, inanimate nature, or technologies) – also involves imagining others’ minds and internal states. We propose that the imaginative process of simulating and projecting internal states is common to both role play and anthropomorphism. The current study investigated the relation between children’s role play and anthropomorphism. Ninety children (5, 7, and 9 years) were administered Individual Differences in Anthropomorphism Questionnaire – Child Form (IDAQ-CF), comprised of the technology-inanimate nature and animal subscales, and the Role Play Scale, which assessed (a) impersonation of animals, people, and/or machines and (b) imaginary companions (ICs), including invisible friends and personified toys. Results indicated that the imaginative act of impersonating an animal, person, and/or machine was positively related to anthropomorphism, and specifically anthropomorphism of inanimate nature and technology. Second, anthropomorphism of animals was highest amongst children with invisible ICs, followed by those with toy ICs and those who impersonated. Finally, children who frequently engaged with an invisible ICs more readily anthropomorphized in general and technology and inanimate nature in particular relative to all other children. Results are discussed in terms of the differing degrees of imagination involved in anthropomorphism of animals versus technology and inanimate nature.

Animacy cues facilitate 10-month-olds' categorization of novel objects with similar insides

In this experiment, we examined whether sensitivity to the relevance of object insides for the categorization of animate objects is in place around 10 months of age. Using an object examining paradigm, 10-month-old infants' (N = 58) were familiarized to novel objects with varying outward appearances but shared insides in one of three groups: No cues, Eyes, and Cue control. During test trials, infants were presented with a novel in-category test object followed by an out-of-category test object. When objects were presented with animacy cues (i.e., Eyes), infants categorized the objects together. In contrast, when objects were presented without any added cues or when they were presented with a shared perceptual marker (Cue control, i.e., plastic spoons placed on top of the objects), infants showed no evidence of categorization. These results indicate that by 10 months of age, eyes signal to infants that objects share some kind of uniting commonality that may not be obvious or readily perceptually available.

Avatars in Pain: Visible Harm Enhances Mind Perception in Humans and Robots

Previous research has shown that when people read vignettes about the infliction of harm upon an entity appearing to have no more than a liminal mind, their attributions of mind to that entity increased. Currently, we investigated if the presence of a facial wound enhanced the perception of mental capacities (experience and agency) in response to images of robotic and human-like avatars, compared with unharmed avatars. The results revealed that harmed versions of both robotic and human-like avatars were imbued with mind to a higher degree, irrespective of the baseline level of mind attributed to their unharmed counterparts. Perceptions of capacity for pain mediated attributions of experience, while both pain and empathy mediated attributions of abilities linked to agency. The findings suggest that harm, even when it appears to have been inflicted unintentionally, may augment mind perception for robotic as well as for nearly human entities, at least as long as it is perceived to elicit pain.

The uncanny valley effect in typically developing children and its absence in children with autism spectrum disorders

Robots and virtual reality are gaining popularity in the intervention of children with autism spectrum disorder (ASD). To shed light on children’s attitudes towards robots and characters in virtual reality, this study aims to examine whether children with ASD show the uncanny valley effect. We varied the realism of facial appearance by morphing a cartoon face into a human face, and induced perceptual mismatch by enlarging the eyes, which has previously been shown as an effective method to induce the uncanny valley effect in adults. Children with ASD and typically developing (TD) children participated in a two-alternative forced choice task that asked them to choose one they liked more from the two images presented on the screen. We found that TD children showed the effect, i.e., the enlargement of eye size and the approaching realism reduced their preference. In contrast, children with ASD did not show the uncanny valley effect. Our findings in TD children help resolve the controversy in the literature about the existence of the uncanny valley effect among young children. Meanwhile, the absence of the uncanny valley effect in children with ASD might be attributed to their reduced sensitivity to subtle changes of face features and their limited visual experience to faces caused by diminished social motivation. Last, our findings provide practical implications for designing robots and virtual characters for the intervention of children with ASD.

Those Virtual People all Look the Same to me: Computer-Rendered Faces Elicit a Higher False Alarm Rate Than Real Human Faces in a Recognition Memory Task

Virtual as compared with real human characters can elicit a sense of uneasiness in human observers, characterized by lack of familiarity and even feelings of eeriness (the “uncanny valley” hypothesis). Here we test the possibility that this alleged lack of familiarity is literal in the sense that people have lesser perceptual expertise in processing virtual as compared with real human faces. Sixty-four participants took part in a recognition memory study in which they first learned a set of faces and were then asked to recognize them in a testing session. We used real and virtual (computer-rendered) versions of the same faces, presented in either upright or inverted orientation. Real and virtual faces were matched for low-level visual features such as global luminosity and spatial frequency contents. Our results demonstrated a higher response bias toward responding “seen before” for virtual as compared with real faces, which was further explained by a higher false alarm rate for the former. This finding resembles a similar effect for recognizing human faces from other than one's own ethnic groups (the “other race effect”). Virtual faces received clearly higher subjective eeriness ratings than real faces. Our results did not provide evidence of poorer overall recognition memory or lesser inversion effect for virtual faces, however. The higher false alarm rate finding supports the notion that lesser perceptual expertise may contribute to the lack of subjective familiarity with virtual faces. We discuss alternative interpretations and provide suggestions for future research.

Kinds of individuals defined by patterns of variables

This paper argues that investigators should consider replacing the popular practice of comparing individuals varying in gender, social class, and/or ethnicity on one or more continuous measures with a search for kinds of individuals defined by patterns of properties that include not only their values on outcome measures but also their gender, social class, and ethnicity. Investigators who believe that a particular predictor contributes to an outcome independent of the gender, class, or ethnicity of the participants often implement statistical procedures that promise to remove the contributions of the above categories. These analyses lead to misleading conclusions when the controlled category is correlated with the dependent measures. The final sections summarize the properties of genders, classes, and ethnic groups that make distinctive contributions to many psychological outcomes. The paper ends by noting that a society's ethical beliefs constitute a defensible basis for ignoring the biological properties associated with these categories in order to allow members of these groups access to whatever educational or occupational goals they desire.

Changes in alpha activity reveal that social opinion modulates attention allocation during face processing

Participants' performance differs when conducting a task in the presence of a secondary individual, moreover the opinion the participant has of this individual also plays a role. Using EEG, we investigated how previous interactions with, and evaluations of, an avatar in virtual reality subsequently influenced attentional allocation to the face of that avatar. We focused on changes in the alpha activity as an index of attentional allocation. We found that the onset of an avatar's face whom the participant had developed a rapport with induced greater alpha suppression. This suggests greater attentional resources are allocated to the interacted-with avatars. The evaluative ratings of the avatar induced a U-shaped change in alpha suppression, such that participants paid most attention when the avatar was rated as average. These results suggest that attentional allocation is an important element of how behaviour is altered in the presence of a secondary individual and is modulated by our opinion of that individual.

The Developmental Origins of Dehumanization

Dehumanization is a complex social phenomenon, intimately connected to intergroup harm and neglect. However, developmental research has only recently started to investigate this important topic. In this chapter, we review research in areas closely related to dehumanization including children's intergroup preferences, essentialist conceptions of social groups, and understanding of relative status. We then highlight the small number of recent studies that have investigated the development of this social bias more directly. We close by making a series of suggestions for future research that will enable us to better understand the nature and causes of this harmful phenomenon.

Perceiving Sophisticated Minds Influences Perceptual Individuation

In six studies, we investigated how ascribing humanlike versus animallike minds to targets influences how easily targets are individuated. Across the studies, participants learned to discriminate among a variety of "aliens" (actually Greebles). Our initial study showed that participants' ability to learn to individuate targets was related to beliefs that targets had sophisticated minds. Investigating the directionality of this relationship, we found that learning to better recognize the targets did not affect perceptions of mind (Study 2). However, when targets were described as having sophisticated humanlike (relative to simplistic animallike) mental faculties, perceivers indicated more motivation to individuate (Study 3) and were more successful individuating them (Studies 4 and 5). Finally, we showed that increased self-similarity mediated the relationship between targets' mental sophistication and perceivers' motivation to individuate (Study 6). These findings indicate ascribing sophisticated mental faculties to others has implications for how we individuate them.

Avoidance of Novelty Contributes to the Uncanny Valley

A hypothesis suggests that objects with a high degree of visual similarity to real humans trigger negative impressions (i.e., the uncanny valley). Previous studies have suggested that difficulty in object categorization elicits negative emotional reactions to enable the avoidance of potential threats. The present study further investigated this categorization-difficulty hypothesis. In an experiment, observers categorized morphed images of photographs and human doll faces as "photograph" or "doll" and evaluated the perceived eeriness of the images. Additionally, we asked the observers to answer questionnaires on behavioral inhibition systems (BIS). The results indicated that individual differences in the BIS score were associated with enhanced eeriness in the objects with a specific human likeness. These findings suggest that the tendency to avoid a potentially threatening novel experience contributes to promoting the perceived eeriness of objects with some degree of visual similarity to real humans.

The Eyes as Windows Into Other Minds

Eyes have been shown to play a key role during human social interactions. However, to date, no comprehensive cross-discipline model has provided a framework that can account for uniquely human responses to eye cues. In this review, I present a framework that brings together work on the phylogenetic, ontogenetic, and neural bases of perceiving and responding to eyes. Specifically, I argue for a two-process model: a first process that ensures privileged attention to information encoded in the eyes and is important for the detection of other minds and a second process that permits the decoding of information contained in the eyes concerning another person's emotional and mental states. To some degree, these processes are unique to humans, emerge during different times in infant development, can be mapped onto distinct but interconnected brain regions, and likely serve critical functions in facilitating cooperative interactions in humans. I also present evidence to show that oxytocin is a key modulator of sensitive responding to eye cues. Viewing eyes as windows into other minds can therefore be considered a hallmark feature of human social functioning deeply rooted in our biology.

Robots As Intentional Agents: Using Neuroscientific Methods to Make Robots Appear More Social

Robots are increasingly envisaged as our future cohabitants. However, while considerable progress has been made in recent years in terms of their technological realization, the ability of robots to interact with humans in an intuitive and social way is still quite limited. An important challenge for social robotics is to determine how to design robots that can perceive the user's needs, feelings, and intentions, and adapt to users over a broad range of cognitive abilities. It is conceivable that if robots were able to adequately demonstrate these skills, humans would eventually accept them as social companions. We argue that the best way to achieve this is using a systematic experimental approach based on behavioral and physiological neuroscience methods such as motion/eye-tracking, electroencephalography, or functional near-infrared spectroscopy embedded in interactive human-robot paradigms. This approach requires understanding how humans interact with each other, how they perform tasks together and how they develop feelings of social connection over time, and using these insights to formulate design principles that make social robots attuned to the workings of the human brain. In this review, we put forward the argument that the likelihood of artificial agents being perceived as social companions can be increased by designing them in a way that they are perceived as intentional agents that activate areas in the human brain involved in social-cognitive processing. We first review literature related to social-cognitive processes and mechanisms involved in human-human interactions, and highlight the importance of perceiving others as intentional agents to activate these social brain areas. We then discuss how attribution of intentionality can positively affect human-robot interaction by (a) fostering feelings of social connection, empathy and prosociality, and by (b) enhancing performance on joint human-robot tasks. Lastly, we describe circumstances under which attribution of intentionality to robot agents might be disadvantageous, and discuss challenges associated with designing social robots that are inspired by neuroscientific principles.

Designing Artificial Agents as Social Companions

When we interact with others, we make inferences about their internal states (i.e., intentions, emotions) and use this information to understand and predict their behavior. Reasoning about the internal states of others is referred to as mentalizing, and presupposes that our social partners are believed to have a mind. Seeing mind in others increases trust, prosocial behaviors and feelings of social connection, and leads to improved joint performance. However, while human agents trigger mind perception by default, artificial agents are not automatically treated as intentional entities but need to be designed to do so. The panel addresses this issue by discussing how mind attribution to robots and other automated agents can be elicited by design, what the effects of mind perception are on attitudes and performance in human-robot and human-machine interaction and what behavioral and neuroscientific paradigms can be used to investigate these questions. Application areas covered include social robotics, automation, driver-vehicle interfaces, and others.

You Look Human, But Act Like a Machine: Agent Appearance and Behavior Modulate Different Aspects of Human-Robot Interaction

Gaze following occurs automatically in social interactions, but the degree to which gaze is followed depends on whether an agent is perceived to have a mind, making its behavior socially more relevant for the interaction. Mind perception also modulates the attitudes we have toward others, and determines the degree of empathy, prosociality, and morality invested in social interactions. Seeing mind in others is not exclusive to human agents, but mind can also be ascribed to non-human agents like robots, as long as their appearance and/or behavior allows them to be perceived as intentional beings. Previous studies have shown that human appearance and reliable behavior induce mind perception to robot agents, and positively affect attitudes and performance in human–robot interaction. What has not been investigated so far is whether different triggers of mind perception have an independent or interactive effect on attitudes and performance in human–robot interaction. We examine this question by manipulating agent appearance (human vs. robot) and behavior (reliable vs. random) within the same paradigm and examine how congruent (human/reliable vs. robot/random) versus incongruent (human/random vs. robot/reliable) combinations of these triggers affect performance (i.e., gaze following) and attitudes (i.e., agent ratings) in human–robot interaction. The results show that both appearance and behavior affect human–robot interaction but that the two triggers seem to operate in isolation, with appearance more strongly impacting attitudes, and behavior more strongly affecting performance. The implications of these findings for human–robot interaction are discussed.

The Impact of Face Inversion on Animacy Categorization

Face animacy perception is categorical: Gradual changes in the real/artificial appearance of a face lead to nonlinear behavioral responses. Neural markers of face processing are also sensitive to face animacy, further suggesting that these are meaningful perceptual categories. Artificial faces also appear to be an “out-group” relative to real faces such that behavioral markers of expert-level processing are less evident with artificial faces than real ones. In the current study, we examined how categorical processing of real versus doll faces was impacted by the face inversion effect, which is one of the most robust markers of expert face processing. We examined how explicit categorization of faces drawn from a real/doll morph continuum was affected by face inversion (Experiment 1) and also how the response properties of the N170 were impacted by face animacy and inversion. We found that inversion does not change the position or steepness of the category boundary measured behaviorally. Further, neural markers of face processing are equally impacted by inversion regardless of whether they are elicited by real faces or doll faces. On balance, our results indicate that inversion has a limited impact on the categorical perception of face animacy.

Human Perception of Animacy in Light of the Uncanny Valley Phenomenon

The uncanny valley hypothesis by Japanese roboticist Masahiro Mori posits a nonlinear relation between human replicas’ human likeness and the emotional responses they elicit. In three studies, we corroborated the uncanny valley hypothesis, using the uncanny phenomenon as a vehicle to shed a new light on human animacy perception. In Study 1, 62 participants rated emotional responses and human likeness of 89 artificial and human faces. In Study 2, another 62 participants conducted a visual looming task with the same 89 faces allowing for the measurement of perceived threat. Results support the uncanny valley hypothesis, suggesting that the uncanny feeling may serve a function to wary humans of the potential danger of entities crossing the animate–inanimate boundary. In Study 3, 36 participants sorted faces as either real or unreal as quickly as possible in a reaction time sorting task allowing for the measurement of categorical uncertainty associated with animacy perception. Faces associated with longer sorting reaction times were also those associated with the highest ratings of negative emotions, suggesting that categorical uncertainty in animacy detection is related to the uncanny feeling. Results are discussed in light of human animacy perception and new directions for future research are suggested.

In dialogue with an avatar, language behavior is identical to dialogue with a human partner

The use of virtual reality (VR) as a methodological tool is becoming increasingly popular in behavioral research as its flexibility allows for a wide range of applications. This new method has not been as widely accepted in the field of psycholinguistics, however, possibly due to the assumption that language processing during human-computer interactions does not accurately reflect human-human interactions. Yet at the same time there is a growing need to study human-human language interactions in a tightly controlled context, which has not been possible using existing methods. VR, however, offers experimental control over parameters that cannot be (as finely) controlled in the real world. As such, in this study we aim to show that human-computer language interaction is comparable to human-human language interaction in virtual reality. In the current study we compare participants' language behavior in a syntactic priming task with human versus computer partners: we used a human partner, a human-like avatar with human-like facial expressions and verbal behavior, and a computer-like avatar which had this humanness removed. As predicted, our study shows comparable priming effects between the human and human-like avatar suggesting that participants attributed human-like agency to the human-like avatar. Indeed, when interacting with the computer-like avatar, the priming effect was significantly decreased. This suggests that when interacting with a human-like avatar, sentence processing is comparable to interacting with a human partner. Our study therefore shows that VR is a valid platform for conducting language research and studying dialogue interactions in an ecologically valid manner.

Identifying Computer-Generated Portraits: The Importance of Training and Incentives

The past two decades have seen remarkable advances in photo-realistic rendering of everything from inanimate objects to landscapes, animals, and humans. We previously showed that despite these tremendous advances, human observers remain fairly good at distinguishing computer-generated from photographic images. Building on these results, we describe a series of follow-up experiments that reveal how to improve observer performance. Of general interest to anyone performing psychophysical studies on Mechanical Turk or similar platforms, we find that observer performance can be significantly improved with the proper incentives.

How social opinion influences syntactic processing-An investigation using virtual reality

The extent to which you adapt your grammatical choices to match that of your interlocutor’s (structural priming) can be influenced by the social opinion you have of your interlocutor. However, the direction and reliability of this effect is unclear as different studies have reported seemingly contradictory results. We have operationalized social perception as the ratings of strangeness for different avatars in a virtual reality study. The use of avatars ensured maximal control over the interlocutor’s behaviour and a clear dimension along which to manipulate social perceptions toward this interlocutor. Our results suggest an inverted U-shaped curve in structural priming magnitude for passives as a function of strangeness: the participants showed the largest priming effects for the intermediately strange, with a decrease when interacting with the least- or most-strange avatars. The relationship between social perception and priming magnitude may thus be non-linear. There seems to be a 'happy medium' in strangeness, evoking the largest priming effect. We did not find a significant interaction of priming magnitude with any social perception.

Differential effects of face-realism and emotion on event-related brain potentials and their implications for the uncanny valley theory

Cartoon characters are omnipresent in popular media. While few studies have scientifically investigated their processing, in computer graphics, efforts are made to increase realism. Yet, close approximations of reality have been suggested to evoke sometimes a feeling of eeriness, the “uncanny valley” effect. Here, we used high-density electroencephalography to investigate brain responses to professionally stylized happy, angry, and neutral character faces. We employed six face-stylization levels varying from abstract to realistic and investigated the N170, early posterior negativity (EPN), and late positive potential (LPP) event-related components. The face-specific N170 showed a u-shaped modulation, with stronger reactions towards both most abstract and most realistic compared to medium-stylized faces. For abstract faces, N170 was generated more occipitally than for real faces, implying stronger reliance on structural processing. Although emotional faces elicited highest amplitudes on both N170 and EPN, on the N170 realism and expression interacted. Finally, LPP increased linearly with face realism, reflecting activity increase in visual and parietal cortex for more realistic faces. Results reveal differential effects of face stylization on distinct face processing stages and suggest a perceptual basis to the uncanny valley hypothesis. They are discussed in relation to face perception, media design, and computer graphics.

Young children perceive less humanness in outgroup faces

We investigated when young children first dehumanize outgroups. Across two studies, 5- and 6-year-olds were asked to rate how human they thought a set of ambiguous doll-human face morphs were. We manipulated whether these faces belonged to their gender in- or gender outgroup (Study 1) and to a geographically based in- or outgroup (Study 2). In both studies, the tendency to perceive outgroup faces as less human relative to ingroup faces increased with age. Explicit ingroup preference, in contrast, was present even in the youngest children and remained stable across age. These results demonstrate that children dehumanize outgroup members from relatively early in development and suggest that the tendency to do so may be partially distinguishable from intergroup preference. This research has important implications for our understanding of children's perception of humanness and the origins of intergroup bias.

Circling Around the Uncanny Valley: Design Principles for Research Into the Relation Between Human Likeness and Eeriness

The uncanny valley effect (UVE) is a negative emotional response experienced when encountering entities that appear almost human. Research on the UVE typically investigates individual, or collections of, near human entities but may be prone to methodological circularity unless the properties that give rise to the emotional response are appropriately defined and quantified. In addition, many studies do not sufficiently control the variation in human likeness portrayed in stimulus images, meaning that the nature of stimuli that elicit the UVE is also not well defined or quantified. This article describes design criteria for UVE research to overcome the above problems by measuring three variables (human likeness, eeriness, and emotional response) and by using stimuli spanning the artificial to human continuum. These criteria allow results to be plotted and compared with the hypothesized uncanny valley curve and any effect observed can be quantified. The above criteria were applied to the methods used in a subset of existing UVE studies. Although many studies made use of some of the necessary measurements and controls, few used them all. The UVE is discussed in relation to this result and research methodology more broadly.

The Eyes Are the Windows to the Mind: Direct Eye Gaze Triggers the Ascription of Others' Minds

Eye gaze is a potent source of social information with direct eye gaze signaling the desire to approach and averted eye gaze signaling avoidance. In the current work, we proposed that eye gaze signals whether or not to impute minds into others. Across four studies, we manipulated targets' eye gaze (i.e., direct vs. averted eye gaze) and measured explicit mind ascriptions (Study 1a, Study 1b, and Study 2) and beliefs about the likelihood of targets having mind (Study 3). In all four studies, we find novel evidence that the ascription of sophisticated humanlike minds to others is signaled by the display of direct eye gaze relative to averted eye gaze. Moreover, we provide evidence suggesting that this differential mentalization is due, at least in part, to beliefs that direct gaze targets are more likely to instigate social interaction. In short, eye contact triggers mind perception.

Of Mannequins and Men

Recent research has demonstrated that ascribing minds to humanlike stimuli is a product of both their perceptual similarity to human faces and whether they engaged configural face processing. We present the findings of two experiments in which we both manipulate the amount of humanlike features in faces (in a doll-to-human morph continuum) and manipulate perceivers’ ability to employ configural face processing (via face inversion) while measuring explicit ratings of mind ascription (Study 1) and the spontaneous activation of humanlike concepts (Study 2). In both studies, we find novel evidence that ascribing minds to entities is an interactive product of both having strong perceptual similarity to human faces and being processed using configural processing mechanisms typical of normal face perception. In short, ascribing mind to others is bounded jointly by the featural cues of the target and by processes employed by the perceiver.

Familiar faces rendered strange: Why inconsistent realism drives characters into the uncanny valley

Computer-modeled characters resembling real people sometimes elicit cold, eerie feelings. This effect, called the uncanny valley, has been attributed to uncertainty about whether the character is human or living or real. Uncertainty, however, neither explains why anthropomorphic characters lie in the uncanny valley nor their characteristic eeriness. We propose that realism inconsistency causes anthropomorphic characters to appear unfamiliar, despite their physical similarity to real people, owing to perceptual narrowing. We further propose that their unfamiliar, fake appearance elicits cold, eerie feelings, motivating threat avoidance. In our experiment, 365 participants categorized and rated objects, animals, and humans whose realism was manipulated along consistency-reduced and control transitions. These data were used to quantify a Bayesian model of categorical perception. In hypothesis testing, we found reducing realism consistency did not make objects appear less familiar, but only animals and humans, thereby eliciting cold, eerie feelings. Next, structural equation models elucidated the relation among realism inconsistency (measured objectively in a two-dimensional Morlet wavelet domain inspired by the primary visual cortex), realism, familiarity, eeriness, and warmth. The fact that reducing realism consistency only elicited cold, eerie feelings toward anthropomorphic characters, and only when it lessened familiarity, indicates the role of perceptual narrowing in the uncanny valley.

Seeing Minds in Others - Can Agents with Robotic Appearance Have Human-Like Preferences?

Ascribing mental states to non-human agents has been shown to increase their likeability and lead to better joint-task performance in human-robot interaction (HRI). However, it is currently unclear what physical features non-human agents need to possess in order to trigger mind attribution and whether different aspects of having a mind (e.g., feeling pain, being able to move) need different levels of human-likeness before they are readily ascribed to non-human agents. The current study addresses this issue by modeling how increasing the degree of human-like appearance (on a spectrum from mechanistic to humanoid to human) changes the likelihood by which mind is attributed towards non-human agents. We also test whether different internal states (e.g., being hungry, being alive) need different degrees of humanness before they are ascribed to non-human agents. The results suggest that the relationship between physical appearance and the degree to which mind is attributed to non-human agents is best described as a two-linear model with no change in mind attribution on the spectrum from mechanistic to humanoid robot, but a significant increase in mind attribution as soon as human features are included in the image. There seems to be a qualitative difference in the perception of mindful versus mindless agents given that increasing human-like appearance alone does not increase mind attribution until a certain threshold is reached, that is: agents need to be classified as having a mind first before the addition of more human-like features significantly increases the degree to which mind is attributed to that agent.

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.

How Well Do Computer-Generated Faces Tap Face Expertise?

The use of computer-generated (CG) stimuli in face processing research is proliferating due to the ease with which faces can be generated, standardised and manipulated. However there has been surprisingly little research into whether CG faces are processed in the same way as photographs of real faces. The present study assessed how well CG faces tap face identity expertise by investigating whether two indicators of face expertise are reduced for CG faces when compared to face photographs. These indicators were accuracy for identification of own-race faces and the other-race effect (ORE)-the well-established finding that own-race faces are recognised more accurately than other-race faces. In Experiment 1 Caucasian and Asian participants completed a recognition memory task for own- and other-race real and CG faces. Overall accuracy for own-race faces was dramatically reduced for CG compared to real faces and the ORE was significantly and substantially attenuated for CG faces. Experiment 2 investigated perceptual discrimination for own- and other-race real and CG faces with Caucasian and Asian participants. Here again, accuracy for own-race faces was significantly reduced for CG compared to real faces. However the ORE was not affected by format. Together these results signal that CG faces of the type tested here do not fully tap face expertise. Technological advancement may, in the future, produce CG faces that are equivalent to real photographs. Until then caution is advised when interpreting results obtained using CG faces.

Artificial faces are harder to remember

Observers interact with artificial faces in a range of different settings and in many cases must remember and identify computer-generated faces. In general, however, most adults have heavily biased experience favoring real faces over synthetic faces. It is well known that face recognition abilities are affected by experience such that faces belonging to "out-groups" defined by race or age are more poorly remembered and harder to discriminate from one another than faces belonging to the "in-group." Here, we examine the extent to which artificial faces form an "out-group" in this sense when other perceptual categories are matched. We rendered synthetic faces using photographs of real human faces and compared performance in a memory task and a discrimination task across real and artificial versions of the same faces. We found that real faces were easier to remember, but only slightly more discriminable than artificial faces. Artificial faces were also equally susceptible to the well-known face inversion effect, suggesting that while these patterns are still processed by the human visual system in a face-like manner, artificial appearance does compromise the efficiency of face processing.

The Face of Humanity

Across three studies, we test the hypothesis that the perceived “humanness” of a human face can have its roots, in part, in low-level, feature-integration processes typical of normal face perception—configural face processing. We provide novel evidence that perceptions of humanness/dehumanization can have perceptual roots. Relying on the well-established face inversion paradigm, we demonstrate that disruptions of configural face processing also disrupt the ability of human faces to activate concepts related to humanness (Experiment 1), disrupt categorization of human faces as human (but not animal faces as animals; Experiment 2), and reduce the levels of humanlike traits and characteristics ascribed to faces (Experiment 3). Taken together, the current findings provide a novel demonstration that dehumanized responses can arise from bottom-up perceptual cues, which suggests novel causes and consequences of dehumanizing responses.

Reducing consistency in human realism increases the uncanny valley effect; increasing category uncertainty does not

Human replicas may elicit unintended cold, eerie feelings in viewers, an effect known as the uncanny valley. Masahiro Mori, who proposed the effect in 1970, attributed it to inconsistencies in the replica's realism with some of its features perceived as human and others as nonhuman. This study aims to determine whether reducing realism consistency in visual features increases the uncanny valley effect. In three rounds of experiments, 548 participants categorized and rated humans, animals, and objects that varied from computer animated to real. Two sets of features were manipulated to reduce realism consistency. (For humans, the sets were eyes-eyelashes-mouth and skin-nose-eyebrows.) Reducing realism consistency caused humans and animals, but not objects, to appear eerier and colder. However, the predictions of a competing theory, proposed by Ernst Jentsch in 1906, were not supported: The most ambiguous representations-those eliciting the greatest category uncertainty-were neither the eeriest nor the coldest.

Navigating a social world with robot partners: A quantitative cartography of the Uncanny Valley

Android robots are entering human social life. However, human-robot interactions may be complicated by a hypothetical Uncanny Valley (UV) in which imperfect human-likeness provokes dislike. Previous investigations using unnaturally blended images reported inconsistent UV effects. We demonstrate an UV in subjects' explicit ratings of likability for a large, objectively chosen sample of 80 real-world robot faces and a complementary controlled set of edited faces. An "investment game" showed that the UV penetrated even more deeply to influence subjects' implicit decisions concerning robots' social trustworthiness, and that these fundamental social decisions depend on subtle cues of facial expression that are also used to judge humans. Preliminary evidence suggests category confusion may occur in the UV but does not mediate the likability effect. These findings suggest that while classic elements of human social psychology govern human-robot social interaction, robust UV effects pose a formidable android-specific problem.

Real or Artificial? Intergroup Biases in Mind Perception in a Cross-Cultural Perspective

Recent research suggests that attributions of aliveness and mental capacities to faces are influenced by social group membership. In this article, we investigated group related biases in mind perception in participants from a Western and Eastern culture, employing faces of varying ethnic groups. In Experiment 1, Caucasian faces that ranged on a continuum from real to artificial were evaluated by participants in the UK (in-group) and in India (out-group) on animacy, abilities to plan and to feel pain, and having a mind. Human features were found to be assigned to a greater extent to faces when these belonged to in-group members, whereas out-group faces had to appear more realistic in order to be perceived as human. When participants in India evaluated South Asian (in-group) and Caucasian (out-group) faces in Experiment 2, the results closely mirrored those of the first experiment. For both studies, ratings of out-group faces were significantly predicted by participants’ levels of ethnocultural empathy. The findings highlight the role of intergroup processes (i.e., in-group favoritism, out-group dehumanization) in the perception of human and mental qualities and point to ethnocultural empathy as an important factor in responses to out-groups.

Arousal, valence, and the uncanny valley: psychophysiological and self-report findings

The main prediction of the Uncanny Valley Hypothesis (UVH) is that observation of humanlike characters that are difficult to distinguish from the human counterpart will evoke a state of negative affect. Well-established electrophysiological [late positive potential (LPP) and facial electromyography (EMG)] and self-report [Self-Assessment Manikin (SAM)] indices of valence and arousal, i.e., the primary orthogonal dimensions of affective experience, were used to test this prediction by examining affective experience in response to categorically ambiguous compared with unambiguous avatar and human faces (N = 30). LPP and EMG provided direct psychophysiological indices of affective state during passive observation and the SAM provided self-reported indices of affective state during explicit cognitive evaluation of static facial stimuli. The faces were drawn from well-controlled morph continua representing the UVH’ dimension of human likeness (DHL). The results provide no support for the notion that category ambiguity along the DHL is specifically associated with enhanced experience of negative affect. On the contrary, the LPP and SAM-based measures of arousal and valence indicated a general increase in negative affective state (i.e., enhanced arousal and negative valence) with greater morph distance from the human end of the DHL. A second sample (N = 30) produced the same finding, using an ad hoc self-rating scale of feelings of familiarity, i.e., an oft-used measure of affective experience along the UVH’ familiarity dimension. In conclusion, this multi-method approach using well-validated psychophysiological and self-rating indices of arousal and valence rejects – for passive observation and for explicit affective evaluation of static faces – the main prediction of the UVH.

Persistence of the uncanny valley: the influence of repeated interactions and a robot's attitude on its perception

The uncanny valley theory proposed by Mori has been heavily investigated in the recent years by researchers from various fields. However, the videos and images used in these studies did not permit any human interaction with the uncanny objects. Therefore, in the field of human-robot interaction it is still unclear what, if any, impact an uncanny-looking robot will have in the context of an interaction. In this paper we describe an exploratory empirical study using a live interaction paradigm that involved repeated interactions with robots that differed in embodiment and their attitude toward a human. We found that both investigated components of the uncanniness (likeability and eeriness) can be affected by an interaction with a robot. Likeability of a robot was mainly affected by its attitude and this effect was especially prominent for a machine-like robot. On the other hand, merely repeating interactions was sufficient to reduce eeriness irrespective of a robot's embodiment. As a result we urge other researchers to investigate Mori's theory in studies that involve actual human-robot interaction in order to fully understand the changing nature of this phenomenon.

Impact of stimulus uncanniness on speeded response

In the uncanny valley phenomenon, the causes of the feeling of uncanniness as well as the impact of the uncanniness on behavioral performances still remain open. The present study investigated the behavioral effects of stimulus uncanniness, particularly with respect to speeded response. Pictures of fish were used as visual stimuli. Participants engaged in direction discrimination, spatial cueing, and dot-probe tasks. The results showed that pictures rated as strongly uncanny delayed speeded response in the discrimination of the direction of the fish. In the cueing experiment, where a fish served as a task-irrelevant and unpredictable cue for a peripheral target, we again observed that the detection of a target was slowed when the cue was an uncanny fish. Conversely, the dot-probe task suggested that uncanny fish, unlike threatening stimulus, did not capture visual spatial attention. These results suggested that stimulus uncanniness resulted in the delayed response, and importantly this modulation was not mediated by the feelings of threat.

Is it the real deal? Perception of virtual characters versus humans: an affective cognitive neuroscience perspective

Recent developments in neuroimaging research support the increased use of naturalistic stimulus material such as film, avatars, or androids. These stimuli allow for a better understanding of how the brain processes information in complex situations while maintaining experimental control. While avatars and androids are well suited to study human cognition, they should not be equated to human stimuli. For example, the uncanny valley hypothesis theorizes that artificial agents with high human-likeness may evoke feelings of eeriness in the human observer. Here we review if, when, and how the perception of human-like avatars and androids differs from the perception of humans and consider how this influences their utilization as stimulus material in social and affective neuroimaging studies. First, we discuss how the appearance of virtual characters affects perception. When stimuli are morphed across categories from non-human to human, the most ambiguous stimuli, rather than the most human-like stimuli, show prolonged classification times and increased eeriness. Human-like to human stimuli show a positive linear relationship with familiarity. Secondly, we show that expressions of emotions in human-like avatars can be perceived similarly to human emotions, with corresponding behavioral, physiological and neuronal activations, with exception of physical dissimilarities. Subsequently, we consider if and when one perceives differences in action representation by artificial agents versus humans. Motor resonance and predictive coding models may account for empirical findings, such as an interference effect on action for observed human-like, natural moving characters. However, the expansion of these models to explain more complex behavior, such as empathy, still needs to be investigated in more detail. Finally, we broaden our outlook to social interaction, where virtual reality stimuli can be utilized to imitate complex social situations.

Visual adaptation of the perception of "life": animacy is a basic perceptual dimension of faces

One critical component of understanding another's mind is the perception of "life" in a face. However, little is known about the cognitive and neural mechanisms underlying this perception of animacy. Here, using a visual adaptation paradigm, we ask whether face animacy is (1) a basic dimension of face perception and (2) supported by a common neural mechanism across distinct face categories defined by age and species. Observers rated the perceived animacy of adult human faces before and after adaptation to (1) adult faces, (2) child faces, and (3) dog faces. When testing the perception of animacy in human faces, we found significant adaptation to both adult and child faces, but not dog faces. We did, however, find significant adaptation when morphed dog images and dog adaptors were used. Thus, animacy perception in faces appears to be a basic dimension of face perception that is species specific but not constrained by age categories.

A review of empirical evidence on different uncanny valley hypotheses: support for perceptual mismatch as one road to the valley of eeriness

The uncanny valley hypothesis, proposed already in the 1970s, suggests that almost but not fully humanlike artificial characters will trigger a profound sense of unease. This hypothesis has become widely acknowledged both in the popular media and scientific research. Surprisingly, empirical evidence for the hypothesis has remained inconsistent. In the present article, we reinterpret the original uncanny valley hypothesis and review empirical evidence for different theoretically motivated uncanny valley hypotheses. The uncanny valley could be understood as the naïve claim that any kind of human-likeness manipulation will lead to experienced negative affinity at close-to-realistic levels. More recent hypotheses have suggested that the uncanny valley would be caused by artificial–human categorization difficulty or by a perceptual mismatch between artificial and human features. Original formulation also suggested that movement would modulate the uncanny valley. The reviewed empirical literature failed to provide consistent support for the naïve uncanny valley hypothesis or the modulatory effects of movement. Results on the categorization difficulty hypothesis were still too scarce to allow drawing firm conclusions. In contrast, good support was found for the perceptual mismatch hypothesis. Taken together, the present review findings suggest that the uncanny valley exists only under specific conditions. More research is still needed to pinpoint the exact conditions under which the uncanny valley phenomenon manifests itself.

Perceptual discrimination difficulty and familiarity in the Uncanny Valley: more like a "Happy Valley"

The Uncanny Valley Hypothesis (UVH) predicts that greater difficulty perceptually discriminating between categorically ambiguous human and humanlike characters (e.g., highly realistic robot) evokes negatively valenced (i.e., uncanny) affect. An ABX perceptual discrimination task and signal detection analysis was used to examine the profile of perceptual discrimination (PD) difficulty along the UVH' dimension of human likeness (DHL). This was represented using avatar-to-human morph continua. Rejecting the implicitly assumed profile of PD difficulty underlying the UVH' prediction, Experiment 1 showed that PD difficulty was reduced for categorically ambiguous faces but, notably, enhanced for human faces. Rejecting the UVH' predicted relationship between PD difficulty and negative affect (assessed in terms of the UVH' familiarity dimension), Experiment 2 demonstrated that greater PD difficulty correlates with more positively valenced affect. Critically, this effect was strongest for the ambiguous faces, suggesting a correlative relationship between PD difficulty and feelings of familiarity more consistent with the metaphor happy valley. This relationship is also consistent with a fluency amplification instead of the hitherto proposed hedonic fluency account of affect along the DHL. Experiment 3 found no evidence that the asymmetry in the profile of PD along the DHL is attributable to a differential processing bias (cf. other-race effect), i.e., processing avatars at a category level but human faces at an individual level. In conclusion, the present data for static faces show clear effects that, however, strongly challenge the UVH' implicitly assumed profile of PD difficulty along the DHL and the predicted relationship between this and feelings of familiarity.