Masahiro Moti and prosthetic arms - Uncanny Valley revisited

With absolute fascination, we listen to Masahiro Moti ["Uncanny Valley Revisited" special session at IROS 2013 in Tokyo], telling us the story of the Uncanny Valley - a concept I had already explored from early on, that now I can comment from a very practical angle.

What are the key issues?

1. Mahsahiro Moti predicts that it is possible to create a safe level of affinity by deliberately pursuing a nonhuman design.

My comments about this:

  • I will fully confirm this from practical experience.
  • A human-like design of a prosthetic arm is not necessary in order for others to feel comfortable. A red hand - as example - or a white shop window mannequin arm may have others feel entirely at ease and serve as communication facilitator.
  • A human-like design can make others really, really, really uneasy.
  • Dynamical appearance heightens the static appearance's impact.

But the Uncanny Valley may be deformed by a proximity effect if it is oneself that is affected. I find that wearing a PVC, rubber or silicone hand is immensely relaxing for myself when I wear it compared to not wearing any. Seeing myself on a photo taken from distance will cause an effect as predicted by the Uncanny Valley - but having my own disabled arm equipped with a human-like prosthesis is extremely relaxing and nice.

Relatively to that, wearing a technical prosthetic arm really is an acquired taste. Finding that not too revolting is an active step. Also, wearing a red hand does require balls. The interesting effect seems to be that wearing non-human prosthetic grippers is far more relaxing for others than it is for me, myself.

So I would extended the Uncanny Valley to include changes to my own body in a different way, thus creating a tension field between the way others see me and the way I see myself; and once one understands that the degree of tension between my own and others' rating of the looks, may be more important for us, as social animals, than the absolute positions on the curves within this diagram. uncanny_valley_wolf

2. Why were we equipped with this eerie sensation? Is it essential for human beings?

I would contend that there are biological reasons why the Uncanny Valley makes sense.

  • I am ill from a common cold today. Looking ill to others when acutely ill has two effects. It can help boosting others' immune response as that seems how we are wired. And it keeps them at a safe distance by feeling disgusted.
  • Looking disgusting to others when chronically ill will have to elicit a social, caring response. When chronically ill, deviation from a healthy normal appearance tends to increase and quite possibly cross the Uncanny Valley.

While thinking deeply about his research, Masahori Moti says he was also listening to his intuitions. There is a deep value in the small things, small notices, one realizes in daily life and that one needs to pick up, that are crucial to accomplish a break through.

Robotics faces steep challenges that can not be overcome by pushing a linear approach.

 3. Other presentations

Marek Michalowski

Marek Michalowski of BeatBots said that he saw robotics as the next step in the illusion of creating life. He then says that few degrees of freedom are better than many, as a few DOF are easier to control. He presented Disney Studio's problem list to revamp initially unpleasing stop motion or cartoon movies (such as Steamboat Willy, a creepy movie from 1928) into attractive motion pictures (such as Snow White and the Seven Dwarves from 1937), later detailed by John Lasseter [1]:

  • Squash and stretch. When an object squashes or stretches, it appears to be made of a pliable material, if it doesn't then it appears rigid. Objects that are partially pliable and partially rigid should have only the pliable parts deform.
  • Timing and motion. The speed of an action, i.e., timing, gives meaning to movement, both physical and emotional meaning. The animator must spend the appropriate amount of time on the anticipation of an action, on the action, and on the reaction to the action. If too much time is spent, then the viewer may lose attention, if too little, then the viewer may not notice or understand the action.
  • Anticipation. Anticipation can be the anatomical preparation for the action, e.g., retracting a foot before kicking a ball. It can also be a device to attract the viewer's attention to the proper screen area and to prepare them for the action, e.g., raising the arms and staring at something before picking it up, or staring off-screen at something and then reacting to it before the action moves on-screen.
  • Staging.Staging is the presentation of an idea so that it is clear. This idea can be an action, a personality, an expression, or a mood. The key idea is that the idea is made clear to the viewer. An important objective of staging is to lead the viewers eye to where the action will occur so that they do not miss anything. This means that only one idea at a time occur, or else the viewers may be looking at the wrong thing. So, the main object should be contrasted in some way with the rest of the scene. A good example is motion, since the eye is drawn to motion in an otherwise still scene. In a scene with everything moving, the eye is drawn to a still object.
  • Straight ahead action and pose to pose. Straight Ahead Action in hand drawn animation is when the animator starts at the first drawing in a scene and then draws all of the subsequent frames until he reaches the end of the scene. This creates very spontaneous and zany looking animation and is used for wild, scrambling action. Pose-to-Pose Action is when the animator carefully plans out the animation, draws a sequence of poses, i.e., the initial, some in-between, and the final poses and then draws all the in-between frames (or another artist or the computer draws the inbetween frames). This is used when the scene requires more thought and the poses and timing are important.
  • Follow through and overlapping action. "It is not necessary for an animator to take a character to one point, complete that action completely, and then turn to the following action as if he had never given it a thought until after completing the first action. When a character knows what he is going to do he doesn't have to stop before each individual action and think to do it. He has it planned in advance in his mind."
  • Slow in and slow out. This refers to the spacing of the inbetween frames at maximum positions. It is the second and third order continuity of motion of the object. Rather than having a uniform velocity for an object, it is more appealing, and sometimes more realistic, to have the velocity vary at the extremes.
  • Arcs. The visual path of action for natural movement.
  • Secondary action. This is an action that directly results from another action. It can be used to increase the complexity and interest in a scene. It should always be subordinate to and not compete with the primary action in the scene. An example might be the facial expression on a character.
  • Exaggeration. Exaggeration does not mean just distorting the actions or objects arbitrarily, but the animator must carefully choose which properties to exaggerate. If only one thing is exaggerated then it may stand out too much. If everything is exaggerated, then the entire scene may appear too unrealistic.
  • Appeal. Appeal means something that the audience will want to see. This is equivalent to charisma in a live actor. A scene or character should not be too simple (boring!) or too complex (can't understand it). One principle to achieve this is to avoid mirror symmetry. Asymmetry tends to be more interesting and appealing.


[1] J. Lasseter, "Principles of traditional animation applied to 3D computer animation," in ACM Siggraph Computer Graphics, 1987, pp. 35-44.
  title={{Principles of traditional animation applied to 3D computer animation}},
  author={Lasseter, John},
  booktitle={{ACM Siggraph Computer Graphics}},

Cite this article:
Wolf Schweitzer: Technical Below Elbow Amputee Issues - Masahiro Moti and prosthetic arms - Uncanny Valley revisited; published 24/11/2013, 08:44; URL:

BibTeX: @MISC{schweitzer_wolf_1627812529, author = {Wolf Schweitzer}, title = {{Technical Below Elbow Amputee Issues - Masahiro Moti and prosthetic arms - Uncanny Valley revisited}}, month = {November},year = {2013}, url = {}}