Masahiro Mori was a Japanese roboticist and professor renowned for ...
#### TL;DR The Uncanny Valley is Masahiro Mori's most influenti...
**A Bunraku puppet** is a traditional Japanese puppet used in a for...
Movement amplifies the uncanny valley effect. The author suggests t...
> ***Thus, because of the risk inherent in trying to increase their...
Interesting thought, that the uncanny valley is really a misapplied...
The Uncanny Valley
By Masahiro Mori (Translated by Karl F. MacDorman and Norri Kageki)
A Valley in One’s
Sense of Affinity
The mathematical term monotonically
increasing function describes a rela-
tion in which the function y ¼ fxðÞ
increases continuously with the
variable x. For example, as effort x
grows, income y increases, or as a car’s
accelerator is pressed, the car moves
faster. This kind of relation is ubiqui-
tous and easily understood. In fact,
because such monotonically increas-
ing functions cover most phenomena
of everyday life, people may fall under
the illusion that they represent all
relations. Also attesting to this false
impression is the fact that many
people struggle through life by persis-
tently pushing without understanding
the effectiveness of pulling back. That
is why people usually are puzzled
when faced with some phenomenon
that this function cannot represent.
An example of a function that does
not increase continuously is climbing
a mountainthe relation between the
distance (x) traveled by a hiker toward
the summit and the hiker’s altitude
(y)owing to the intervening hills
and valleys. I have noticed that, in
climbing toward the goal of making
robots appear like a human, our affin-
ity for them increases until we come
to a valley (Figure 1), which I call the
uncanny valley.
Nowadays, industrial robots are
increasingly recognized as the driving
force behind reductions in factory
personnel. However, as is well known,
these robots just extend, contract, and
rotate their arms; without faces or legs,
they do not look human. Their design
policy is clearly based on functionality.
From this standpoint, the robots must
perform functions similar to those of
human factory workers, but whether
they look similar does not matter. Thus,
given their lack of resemblance to
human beings, in general, people hardly
feel any affinity for them. (Note: How-
ever, industrial robots are considerably
closer in appearance to humans than
general machinery, especially in their
arms.) If we plot the industrial robot on
ness, it lies near the origin in Figure 1.
In contrast, a toy robot’s designer
may focus more on the robot’s appear-
ance than its functions. Consequently,
despite its being a sturdy mechanical
figure, the robot will start to have a
roughly human-looking external form
with a face, two arms, two legs, and a
torso. Children seem to feel deeply
attached to these toy robots. Hence,
the toy robot is shown more than half-
way up the first hill in Figure 1.
Since creating an artificial human is
itself one of the objectives of robotics,
various efforts are underway to build
humanlike robots. (Note: Others believe
that the true appeal of robots is their
potential to exceed and augment humans.)
For example, a robot’s arm may be com-
posed of a metal cylinder with many
bolts, but by covering it with skin and
adding a bit of fleshy plumpness, we can
achieve a more humanlike appearance.
As a result, we naturally respond to it
with a heightened sense of affinity.
Many of our readers have experi-
ence interacting with persons with
physical disabilities, and all must have
felt sympathy for those missing a hand
or leg and wearing a prosthetic limb.
Recently, owing to great advances in
fabrication technology, we cannot dis-
tinguish at a glance a prosthetic hand
from a real one. Some models simulate
wrinkles, veins, fingernails, and even
fingerprints. Though similar to a real
hand, the prosthetic hand’s color is
Digital Object Identifier 10.1109/MRA.2012.2192811
Date of publication: 6 June 2012
JUNE 2012
Editor’s note: More than 40 years ago, Masahiro Mori, a robotics
professor at the Tokyo Institute of Technology, wrote an essay [1]
on how he envisioned people’s reactions to robots that looked
and acted almost like a human. In particular, he hypothesized that
a person’s response to a humanlike robot would abruptly shift
from empathy to revulsion as it approached, but failed to attain, a
lifelike appearance. This descent into eeriness is known as the
uncanny valley. The essay appeared in an obscure Japanese jour-
nal called Energy in 1970, and in subsequent years, it received
almost no attention. However, more recently, the concept of the
uncanny valley has rapidly attracted interest in robotics and other
scientific circles as well as in popular culture. Some researchers
have explored its implications for humanrobot interaction and
computer-graphics animation, whereas others have investigated
its biological and social roots. Now interest in the uncanny valley
should only intensify, as technology evolves and researchers build
robots that look human. Although copies of Mori’s essay have circu-
lated among researchers, a complete version hasn’t been widely
available. The following is the first publication of an English transla-
tion that has been authorized and reviewed by Mori. (See “Turning
Point” in this issue for an interview with Mori.)
pinker as if it had just come out of
the bath.
One might say that the prosthetic
hand has achieved a degree of resem-
blance to the human form, perhaps
on par with false teeth. However, once
we realize that the hand that looked
real at first sight is actually artificial,
we experience an eerie sensation. For
example, we could be startled during a
handshake by its limp boneless grip
together with its texture and coldness.
When this happens, we lose our sense
of affinity, and the hand becomes
uncanny. In mathematical terms, this
can be represented by a negative value.
Therefore, in this case, the appearance
of the prosthetic hand is quite human-
like, but the level of affinity is negative,
thus placing the hand near the bottom
of the valley in Figure 1.
I don’t think that, on close inspec-
tion, a bunraku puppet appears similar
to a human being. Its realism in terms
of size, skin texture, and so on, does not
even reach that of a realistic prosthetic
hand. But when we enjoy a puppet
show in the theater, we are seated at a
certain distance from the stage. The
puppet’s absolute size is ignored, and
its total appearance, including hand
and eye movements, is close to that of a
human being. So, given our tendency
as an audience to become absorbed in
this form of art, we might feel a high
level of affinity for the puppet.
From the preceding discussion, the
readers should be able to understand the
concept of the uncanny valley. Now let
us consider in detail the relation between
the uncanny valley and movement.
The Effect of Movement
Movement is fundamental to ani-
malsincluding human beingsand
thus to robots as well. Its presence
changes the shape of the uncanny val-
ley graph by amplifying the peaks and
valleys (Figure 2). For illustration,
when an industrial robot is switched
off, it is just a greasy machine. But
once the robot is programmed to
move its gripper like a human hand,
we start to feel a certain level of affin-
ity for it. (In this case, the velocity,
acceleration, and deceleration must
approximate human movement.)
Conversely, when a prosthetic hand
that is near the bottom of the uncanny
valley starts to move, our sensation of
eeriness intensifies.
Some readers may know that re-
cent technology has enabled prosthetic
hands to extend and contract their fin-
gers automatically. The best commer-
cially available model, shown in Figure
3, was developed by a manufacturer in
Vienna. To explain how it works, even
if a person’s forearm is missing, the
intention to move the fingers produces
a faint current in the arm muscles,
which can be detected by an electro-
myogram. When the prosthetic hand
detects the cur-
rent by means of
electrodes on the
skin’s surface, it
amplifies the sig-
nal to activate a
small motor that
moves its fingers.
As this myoelec-
tric hand makes
movements, it
could make healthy people feel uneasy.
If someone wearing the hand in a dark
Uncanny Valley
Healthy Person
Bunraku Puppet
Prosthetic Hand
Toy Robot
Industrial Robot
Affinity (Shinwakan)
Human Likeness 50% 100%
Figure 1. The graph depicts the uncanny valley, the proposed relation between the
human likeness of an entity, and the perceiver’s affinity for it. [Translators’ note: Bunraku
is a traditional Japanese form of musical puppet theater dating to the 17th century. The
puppets range in size but are typically a meter in height, dressed in elaborate costumes,
and controlled by three puppeteers obscured only by their black robes (see front cover).]
Uncanny Valley
Healthy Person
Bunraku Puppet
Prosthetic Hand
Humanoid Robot
Industrial Robot
Affinity (Shinwakan)
Human Likeness 50% 100%
Ill Person
Okina Mask
Ordinary Doll
Myoelectric Hand
Yase Otoko Mask (Noh Play)
Figure 2. The presence of movement steepens the slopes of the uncanny valley. The
arrow’s path represents the sudden death of a healthy person. [Translators’ note: Noh is
a traditional Japanese form of musical theater dating to the 14th century in which
actors commonly wear masks. The yase otoko mask bears the face of an emaciated
man and represents a ghost from hell. The okina mask represents an old man.]
possible to create a
safe level of affinity by
deliberately pursuing
JUNE 2012
place shook a woman’s hand with it,
the woman would assuredly shriek.
Since the negative effects of move-
ment are apparent even with a pro-
sthetic hand, to build a whole robot
would magnify the creepiness. This is
just one robot. Imagine a craftsman
being awakened suddenly in the dead
of the night. He searches downstairs for
something among a crowd of manne-
quins in his workshop. If the manne-
quins started to move, it would be like
Movement-related effects could be
observed at the 1970 World Exposi-
tion in Osaka, Japan. Plans for the
event had prompted the construction
of robots with some highly sophisti-
cated designs. For example, one robot
had 29 pairs of artificial muscles in
the face (the same number as a human
being) to make it smile in a humanlike
fashion. According to the designer, a
smile is a dynamic sequence of facial
deformations, and the speed of the
deformations is crucial. When the
speed is cut in half in an attempt to
make the robot bring up a smile more
slowly, instead of looking happy, its
expression turns creepy. This shows
how, because of a variation in move-
ment, something that has come to
appear close to humanlike a robot,
puppet, or prosthetic handcould
easily tumble down into the uncanny
Escape by Design
We hope to design and build robots
and prosthetic hands that will not fall
into the uncanny valley. Thus, because
of the risk inherent in trying to
increase their degree of human like-
ness to scale the second peak, I recom-
mend that designers instead take the
first peak as their goal, which results in
a moderate degree of human likeness
and a considerable sense of affinity. In
fact, I predict that it is possible to cre-
ate a safe level of affinity by deliber-
ately pursuing a nonhuman design. I
ask designers to ponder this. To illus-
trate the principle, consider eyeglasses.
Eyeglasses do not resemble real eye-
balls, but one could say that their
design has created a charming pair of
new eyes. So we should follow the
same principle in designing prosthetic
hands. In doing so, instead of pitiful-
looking realistic hands, stylish ones
would likely become fashionable.
As another example, consider this
model of a human hand created by a
woodcarver who sculpts statues of
Buddhas (Figure 4). The fingers bend
freely at the joints. The hand lacks fin-
gerprints, and it retains the natural
color of the wood, but its roundness
and beautiful curves do not elicit any
eerie sensation. Perhaps this wooden
hand could also serve as a reference
for design.
An Explanation of the Uncanny
As healthy persons, we are repre-
sented at the second peak in Figure 2
(moving). Then when we die, we are
unable to move; the body goes cold,
and the face becomes pale. Therefore,
our death can be regarded as a move-
ment from the second peak (moving)
to the bottom of the uncanny valley
(still), as indicated by the arrow’s path
in Figure 2. We might be glad that this
arrow leads down into the still valley
of the corpse and not the valley ani-
mated by the living dead.
I think this descent explains the
secret lying deep beneath the uncanny
valley. Why were we equipped with
this eerie sensation? Is it essential for
human beings? I have not yet consid-
ered these questions deeply, but I have
no doubt it is an integral part of our
instinct for self-preservation. (Note:
The sense of eeriness is probably a
form of instinct that protects us from
proximal, rather than distal, sources
of danger. Proximal sources of danger
include corpses, members of different
species, and other entities we can closely
approach. Distal sources of danger
include windstorms and floods.)
We should begin to build an accu-
rate map of the uncanny valley so that
through robotics research we can begin
to understand what makes us human.
This map is also necessary to create
using nonhuman designsdevices to
which people can relate comfortably.
(Notes given in parentheses are foot-
notes in the original article.)
[1] M. Mori, “The uncanny valley,” Energy,
vol. 7, no. 4, pp. 3335, 1970 (in Japanese).
Karl F. MacDorman is an associate
professor at the School of Informatics,
Indiana University.
Norri Kageki is a business and tech-
nology writer based in Silicon Valley
and the founder of
Figure 4. A model of a hand created by a
woodcarver of Buddha statues. Reprinted
from [1] with permission.
Figure 3. A human arm (top left)
controls a realistic myoelectric hand,
called the “Vienna Hand.” Reprinted from
[1] with permission.
JUNE 2012
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#### TL;DR The Uncanny Valley is Masahiro Mori's most influential paper. This paper explores how people's emotional response to robots changes as they become more human-like. The main takeaways are: - **Uncanny valley** refers to a decrease in affinity as robots start to look more human. - factors like **movement, realism and behavior influence the magnitude uncanny valley effect. ** - movement can dramatically influence influence that effect Developers and designers in robotics and artificial intelligence encounter these challenges as they build robots and AIs meant to interact with humans. The uncanny valley theory has become a foundational concept related to human-computer interaction, psychology, and robotics. **A Bunraku puppet** is a traditional Japanese puppet used in a form of puppet theater called Bunraku, which originated in Osaka in the 17th century. Here is a video of [Bunraku Puppet Theater]( !["bunraku"]( You can also learn more here: [Bunraku]( Masahiro Mori was a Japanese roboticist and professor renowned for his work in robotics and for conceptualizing the theory of the "Uncanny Valley". He made significant contributions to the field of robotics and human-robot interaction influencing how humans perceive and react to human like "beings". ![]( An interview with Masahiro Mori: [An Uncanny Mind: Masahiro Mori on the Uncanny Valley and Beyond ]( Interesting thought, that the uncanny valley is really a misapplied reaction to an instinctive fear of a corpse? Movement amplifies the uncanny valley effect. The author suggests that a moving humanoid that falls into the uncanny valley will create a stronger negative response than a still one. > ***Thus, because of the risk inherent in trying to increase their degree of human likeness to scale the second peak, I recommend that designers instead take the first peak as their goal, which results in a moderate degree of human likeness and a considerable sense of affinity. ***