Subjective Ratings of Robot Video Clips for Human Likeness,
Familiarity, and Eeriness: An Exploration of the Uncanny Valley
Karl F. MacDorman

Introduction
To build robots that at least superficially approach human likeness is leading to insights in human perception
and face-to-face interaction. These android robots possess the physical presence that simulated characters lack,yet can be more perfectly controlled than any humanactor, to isolate the factor under study. Even in experiments in which the android’s responses are identical, we can observe how human responses vary according to their beliefs. For example, Japanese participants
showed the same modesty with their eyes by avertinggaze downward when interacting with an android as
when interacting with a human interlocutor if they believed the android were under human control by telepresence [MacDorman et al., 2005].
In addition, androids provide an ideal testing groundfor theories from the social and cognitive sciences because competing models can be implemented in an android and then tested by letting the android interact withfamiliarity

Masahiro Mori observed that as robots come to look
more humanlike, they seem more familiar, until a pointis reached at which subtle deviations from human norms
cause them to look creepy. He referred to this dip in familiarity and corresponding surge in strangeness as theuncanny valley. The eerie sensation associated with amismatch between human expectations and a robot’s
behavior provides a useful source of feedback to improvethe cognitive models implemented in the robot. Is theuncanny valley a necessary property of near-humanlike
forms? This paper contributes to ongoing work in understanding the nature and causes of the uncanny valley
by means of an experiment: 56 participants were asked
to rate 13 robots and 1 human, shown in video clips, ona very mechanical (1) to very humanlike (9) scale, a very
strange (1) to very familiar (9) scale, and a not eerie (0)to extremely eerie (10) scale. Contrary to earlier studies
with morphs [MacDorman and Ishiguro, 2006], plots ofaverage and median values for ratings on these scales
do not reveal a single U-shaped valley as predicted by
Mori’s uncanny valley hypothesis [1970], although hishypothesis allows for some variation owing to movement.
Robots rated similarly on the mechanical versus humanlike scale can be rated quite differently on the strange
versus familiar or the eeriness scales. The results indicate that the perceived human likeness of a robot is
not the only factor determining the perceived familiarity,
strangeness, or eeriness of the robot. This suggests that
other factors could be manipulated to vary the familiarity, strangeness, or eeriness of a robot independently of
its human likeness.

uncanny valley
movingstill{Abstract+School of Informatics, Indiana University, USA

bunraku puppet
humanoid robot

healthy
personstuffed animalindustrial robot

human likeness50%
corpse100%
prosthetic handzombieFigure 1: Mori hypothesized the relation between humanlikeness and perceived familiarity: familiarity increases withhuman likeness until an uncanny valley is reached causedby sensitivity to perceived imperfections in near-humanlike
forms [Mori, 1970]. Movement, according to Mori, magnifies
the uncanny valley.

people [MacDorman and Ishiguro, 2006]. Androids provide not only a platform for integrating techniques fromscience and engineering but also for studying the relationship between interaction and cognitive mechanism.
Thus, they may one day provide an avenue for unifying
the behavioral sciences and cognitive neuroscience.
Recent evidence indicates that androids are generally better able to elicit human-directed norms
of interaction than less humanlike robots or animated characters [MacDorman and Ishiguro, 2006][Cowley and MacDorman, 2006].
However, Mori
[1970] observed a heightened sensitivity to defects innear-humanlike forms—an uncanny valley in what isotherwise a positive relationship between human likeness and familiarity (Fig. 1). Although Mori proposedthat abstract human forms should serve as the principle
for designing socially-acceptable robots, the uncanny
valley can be seen more positively—for example, byindicating when a robot’s responses do not rise to theexpectations elicited by its human form. This provides
useful feedback for improving the cognitive models
implemented in the android (see Fig. 6).

123

4

5

6

78

910

11

12345678910

1189881177967 1167586551091086
1 244346334 51435324225238111719217 11 8 10900123456

Very mechanical

789

Very humanlike

Figure 2: Average ratings for strange versus familiar (solidline) and eeriness (dashed line) were plotted against mechanical versus humanlike for images morphing from the robot
Qrio the Philip K. Dick android to Philip K. Dick himself.
The plots reproduce Mori’s hypothesized uncanny valley andindicate a corresponding region of eeriness.

Plotting the uncanny valley
In a previous study, 45 Indonesian participants wereasked to rate 31 images on a nine-point scale ranging from very mechanical (1) to very humanlike(9) and from very strange (1) to very familiar (9)[MacDorman and Ishiguro, 2006]. They were then asked
to select eerie images and rate them for eeriness on a tenpoint scale, ranging from slightly eerie (1) to extremely
eerie (10).1 Two sets of 11 morphed images were included among the 31 images.
Fig. 2 shows the plot of the average ratings on thestrange versus familiar (solid line) and eeriness (dashedline) scale for the first set of images, which morphedfrom a photograph of the humanoid robot Qrio (left) toone of the Philip K. Dick android developed by Hanson Robotics (center) to one of Philip K. Dick himself(right). Fig. 3 shows the plot for a second set of images,
which morphed from a photograph of the humanoid robot Eveliee (left) to one of the android Repliee Q1Expo(center) to Repliee’s human model (right). The independent axis is the average rating on the mechanical versus
humanlike scale. The plots reproduce Mori’s posited uncanny valley (solid line) and indicate a region of eerinessin the same area (dashed line).

Experiment: Ratings of videos
The intention of the current study is to determine
whether the uncanny valley is a necessary property ofnear-humanlike forms. Participants are presented withshort video clips of a wide range of mainly android andhumanoid robots engaged in various activities in different settings.
161

10Images that were not selected as eerie were rated 0.

1
Very mechanical234567

Very humanlike

Figure 3: The same plots as Fig. 2 but for images morphingfrom the robot Eleviee to the android Repliee Q1Expo to theandroid’s human model.

Subjects. There were 56 Indonesian participants, 43
male and 13 female, of whom 13 were 17 to 20 years
old, 36 were 21 to 25, 4 were 26 to 30, and 3 were 31
to 35. The participants were mainly university students,
young professionals, and government workers. Participants were recruited from an Internet cafe and received
two hours of free Internet access.
Procedure. Participants were asked on a computerbased questionnaire, in individual sessions, to rate 14
video clips, most of which were 30 to 60 seconds inlength, on a nine-point mechanical versus humanlike
scale, a nine-point strange versus familiar scale, and aten-point eeriness scale. The scales ranged from very mechanical (1) to very humanlike (9), from very strange (1)to very familiar (9), and from not eerie (0) to extremely
eerie (10). The video clips included a mobile robot (Pioneer II), a manipulator arm, seven humanoid robots(Rovovie-M3, HR-2, VisiON Nexta, Chronio, Robovie,
Wakamaru, Asimo), two android heads (K-bot, Eva),
two androids (Philip K. Dick, Repliee Q1Expo), and one
human being. The video clips were presented in random
order. For each video the three ratings were requested
in random order. The direction of the scales was determined randomly for each question.
Results. Fig. 4 shows the plot of the average ratings
on the strange versus familiar (solid line) and eeriness(dashed line) scale for a given average rating on the mechanical versus humanlike scale for the video clips of the14 robots. There is no consistent valley shape when plotting familiarity against human likeness. Instead, there
are oscillations in eeriness for robots that range from mechanical looking (1.96) to approaching very humanlike(8.57). The plot of strange versus familiar and eerinessare almost mirror images.
The average standard deviation (SD) was 1.69 for themechanical versus humanlike scale, 2.43 for the strange

612

Table 1: Median ratings of the 14 video clips on a very
5

mechanical (1) to very humanlike (9) scale and a very strange(1) to very familiar (9) scale

11No.
12345678910111412131043928114713814761025 63812451317114939211173113625 84141012012345678Very mechanical

9Very humanlike

Figure 4: Based on the average ratings of 56 participants, 14

Very familiar

video clips are arranged from left, mechanical, to right, approaching very humanlike. The names of the robots are listed
in Table 1. The solid line plots the relationship between perceived humanlikeness (on the mechanical versus humanlikescale) and perceived familiarity (on the strange versus familiar scale). The dashed line plots the relationship between
perceived humanlikeness and eeriness. There is no single uncanny valley in the plot.
9148
1073625456781213

14119

Very strange

3

Name
Manipulator
Pioneer IIHR-2
Robovie-M3
Nexta
Chronio
Wakamaru
Robovie
K-bot
Asimo
Eva
HumanRepliee
PKD android

mech. v hum.
22
3
3
4
4
4
4
67
7
9
99strange v fam.
54
65
65.5
54.5
373.5
85.5
5

versus familiar scale, and 1.68 for the eeriness scale.
Median values were considered a more robust indicatorof central tendency, especially given the high variance inthe data and the the subjective nature of the questions.
Table 1 lists the values for the mechanical versus humanlike and strange versus familiar scales. The medianvalues for the eerie scale are not listed because they were
all 0 except for K-bot whose median value was 1. Fig. 5
plots the median values for the strange verus familiar
scale against the median values for the mechanical versus humanlike scale.
Table 1 and Fig. 5 show that video clips of robots
that were rated as having the same median human likeness could have much more or much less median familiarity. For example, the median value was very humanlike (9) for the Philip K. Dick android, Repliee Q1Expo,and its human model, although the median value for thehuman model was familiar (8) but neutral (5) for thePhilip K. Dick android and near neutral (5.5) for Repliee
Q1Expo. The median values also represent Asimo as
somewhat familiar and K-bot as somewhat strange, although Asimo was represented as more humanlike thanK-bot. Thus, the depiction of Asimo in the video clip
seemed to bump up its human likeness despite the factthat it does not have a humanlike face with skin, teeth,
nostrils, pupils, and so on.

Discussion

21
1

2

Very mechanical

3

4

5

6

7

8

9

Very humanlike

Figure 5: The median ratings on a strange versus familiar
scale are plotted against the median ratings on a mechanicalversus humanlike scale for the robots in Table 1 and Fig. 4.
Robots with the same median value for human likeness canshow quite different median values for familiarity.

The video clips exhibit a wide range of robots performing different actions in quite different contexts, sometimes with speech accompaniment. The results do notindicate a single uncanny valley for a particular range ofhuman likeness. Rather, they suggest that human likeness is only one of perhaps many factors influencing theextent to which a robot is perceived as being strange,
familiar, or eerie. This is an important result because it
implies that factors other than human likeness could beThe Synthetic Methodology
Analysis ofmechanisms
underlyinghuman activity{Social Psychology
Cognitive Psychology
Cognitive Neuroscience
Hypothesis
verification

Developmentof humanlike
electromechanicaldevices{HumanBeing

Hypothesis
formation
Android
Artificial Intelligence
Pattern Recognition
Control Systems
Mechanical Engineering
Materials Science

Human-robot interaction
Integration of science and engineering

Figure 6: Ishiguro [2005] proposes a synthetic methodology
for investigating human interaction that integrates scienceand engineering.

manipulated to overcome the uncanny valley. Of course,
Mori [1970] [Mori, 1970] identified motion as one suchfactor, so it may be argued that his hypothesis could accommodate the results. But the variations in familiarityand eeriness for a given level of human likeness are notconsistent with motion-induced magnifications of a valley shape.
So why does morphing from a mechanical-looking robot to an android and then to its human model produce
an uncanny valley in still images, as shown in Fig. 2 and3? One possible explanation is that the morphs provide
a more gradual and consistent change with less extraneous variation. For example, as the images were still,variations in movement and speech were not an issue.
We might expect to find uncanny valleys in more controlled experiments that vary appearance or movement
along fewer parameters.
The notion that the uncanny valley can be escapedby varying factors unrelated to human likeness is consistent with an experiment performed by Hanson [2006]
using morphs. Although he found that morphing from amechanical-looking robot to an android produced a valley in a familiarity scale and in an appealing scale anda peak in an eeriness scale, these effects were greatly reduced by tuning the morphs. Thus, without making amorph more or less humanlike, Hanson was largely able
to design around the uncanny valley. His technique wasto adjust the appearance of the uncanny morphs toward
the cuter features of a doll.

Conclusion
The results of the experiment suggest that human likeness is only one factor determining the familiarity,
strangeness, and eeriness of a robot. This offers thehope that other factors modulating these qualities will
be uncovered. MacDorman and Ishiguro [2006] have documented a number of possible explanations for the uncanny valley, ranging from expectation violation and cog-nitive paradoxes [Ramey, 2005] to evolutionary aesthetics [Etcoff, 1999] and pathogen avoidance. As the validity of these explanations comes under scientific scrutiny,
design principles will appear that engineers can use todevelop robots with desirable aesthetics. Whether it isindeed desirable to build a robot that is appealing orunnerving will depend on its purpose and the setting inwhich it is used. Given the success of the horror genre,
it is clear that eeriness is not always considered a badthing.

Acknowledgments
Much appreciation goes to Heryati Madiapuri for recruiting participants and conducting the experiments in September, 2005, to Yuli Suliswidiawati, for reviewing theexperimental procedures, and to Z. A. Dwi Pramono andChristopher H. Ramey for serving on the ethics advisory panel and providing comments on the experimental
design. Thanks also go to David Hanson, Almir Heralik, Takayuki Kanda, Hiroshi Ishiguro, Takahashi Tomotaka, ActivMedia Robots, ATR, Honda, Kokoro Co.,
Ltd., Mitsubishi, and Vstone for the robots.

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