The hand stigma myth and 'sociable' prosthetics

My own experience is that a life-like silicon hand (or glove) has a tendency to make other people really nervous.

Reportedly, it causes them to check constantly whether it is fake or not. It can be visually irritating and constitute a permanent visual magnet.

Even close friends or family reported the experience to be relatively stressful.

People not associated with me may praise the quality of a cosmetic glove's imitation quality - but from my view and what I discussed with various folks, I have to say such feedback has to be strongly weighted and categorized into compliment versus their own opinion.

Far less stressful appeared to be the appearance of the red color 'on one hand' and the Becker Lock Grip hand 'on the other' (waah, these 'one hand other hand' puns are funny aren't they) - that was almost unanimously greeted with curiosity or friendliness, that got people to laugh from joy, that had people grab it and touch it without asking. I mean, those were instant gut reactions, not slowly carefully thought out patterns.

But also a steel hook was reported to make other people feel not nearly as tense as the mimicry attempt of so-called life like prosthetic appearance of my hand. Hooks - if anything - intimidate and frighten little boys or people that still are little boys (link) mostly based on mythical and legendary beliefs.

So I am not sure what psycho-physical studies are cited when comparing the impact of a well drafted artificial look and a good life-like imitation - but current artistic prosthesis designs all avoid to simulate real skin with very good reason.

So what do we get to read now? In arXiv:0909.3559v1 [physics.med-ph] Towards Humanlike Social Touch for Sociable Robotics and Prosthetics: Comparisons on the Compliance, Conformance and Hysteresis of Synthetic and Human Fingertip Skins by John-John Cabibihan, Stephane Pattofatto, Moez Jomaa, Ahmed Benallal and Maria Chiara Carrozza, we read this recently published [September 2009] paragraph:

Any disfigurement of the hand, which is among the easily noticed part of the body, certainly affects the psychological well-being. The reported effects of amputation are depression, feelings of hopelessness, low self-esteem, fatigue, anxiety and sometimes suicidal ideation of the patient [5]. It was found that concealment of prosthesis usage is an effective coping strategy so that the prosthetic users can integrate socially and prevent stigmatization [6]. For this purpose, modern prosthetic hands are being made with very human like appearances.

So clearly, this is not just about robots or mannequins - it is also about humans wearing artificial arms.

They continue to go all the way to spend effort and time to identify what's wrong with current attempts at simulation of human skin and how to measure specifics of an optimal skin model. All nice and sweet.

But the paper misses a number of significant points.

  • Proprioception through a prosthetic hand replacement suffers from every layer that is soft. My Otto Bock voluntary opening hand essentially is a metal hook covered by thick plastic, that then is covered with a cosmetic silicone glove. I can forget proprioception there. With my hook as well as the uncovered Becker Lock Grip hand, hard structures provide feedback about touch and resistance.
  • All kinds of materials are agreeable to touch. Not just skin. Leather, cotton, wool, synthetic fabric, metal, wood are all not even mentioned in that article. They point to Otto Bock's PVC glove - but that is not a skin simulation - that is comparatively well gliding and cheap material sold at a premium, it does not aim to satisfy touch or looks criteria. But practical aspects matter! If you want to put on a jacket and require the glove to slide well through the sleeve, using a PVC glove is great - and silicone sucks. I once spent a while in shop trying on virtually every jacket they had there: none of them had a sleeve where my cosmetic silicone glove would slide through.
  • The Uncanny Valley. Apparent similarity of a prosthetic hand to a real hand is achieved only very partly through static similarity. Motion is far more important to achieve a sense of similarity. As a realistically moving prosthetic hand is not available, both today's most advanced bionic hands - iLimb, Michelangelo - ship with white transparent or similarly industrially designed gloves. Personally, I think it is great like that. My own experience with a red hand and red prosthetic socket is very positive. But there is no indication both on theory and practice of hand prosthetics that life-like skin is the solution to better integration. It can be helpful and important in certain situations - and it may be stressful or impractical in others.

However, the underlying premise seems to be this piece of controversial assumption right here:

http://www.technologyreview.com/blog/arxiv/24152/

When it comes to building realistic robots, it's not just the way they look that's important. It's also the way they feel to the touch, says John-John Cabibihan at the National University of Singapore and pals. They argue that if robots are ever to be accepted socially, they will need to have human like skin so that actions such as handshakes can be made as realistic as possible.

I do not understand one thing though. All kinds of real people - that have human skin as real, as authentic, as alive and as realistic as it ever gets - are not accepted very well into society, for any deliberate reason such as culture, race, ethnicity, gender or other. Moreover, disabled people still have serious problems being accepted in society despite most of them being covered with entirely real human skin from head to toes.

So really the point is missed unless, of course, thoughts will be presented whether the newly developed skin also has to be white (for better social acceptance)? Until then I believe that if the authors of the study find themselves less accepted in society it's maybe not so much due to their unrealistic fingertip skin compliance as due to their peculiar sense of humor.

Far more to the point are current research endeavors that characterize various materials for the subjective touch quality, e.g. in automotive industry: there, the feel of living room sofas is increasingly abandoned for fabrics that are optimized for the hedonic pleasure they generate - not for their similarity to a non-existent reality. In other words that industry realized they leave behind generation of simulacra for the generation of new realities.

So here is the requirement list for surfaces to prosthetic/robot hands to integrate into society:

  • Look cool (hint: this one is subjective - so if you are a manufacturer this one spells out as choice or range of options; here is how to sew textile patterns).
  • Look as life-like as required but not more (hint: this likely affects dynamic more than static appearance - so if you cannot even get the motion right, why be overly concerned with static looks).
  • Grip side: no slip, somehwat sticky yet easy to clean and easy to swap individually (manufacturers: hard one, this one, isn't it).
  • Non-grip side: slippery, smooth, not rubbery, not sticky.
  • The whole surface should be easy to swap as a whole.
  • Subjective feel for grip: check automotive industry and their research into the hedonistic qualities of touch. Wood, leather, hard plastic or some sort of textile may be more pleasant to shake hands with. If real skin was the most pleasant surface type to touch, we'd at least be finding that type of feeling all over today's cars - but we are not. Seriously, there are reasons for this.

Cite this article:
Wolf Schweitzer: Technical Below Elbow Amputee Issues - The hand stigma myth and 'sociable' prosthetics; published October 9, 2009, 01:24; URL: https://www.swisswuff.ch/tech/?p=225.

BibTeX: @MISC{schweitzer_wolf_1582669074, author = {Wolf Schweitzer}, title = {{Technical Below Elbow Amputee Issues - The hand stigma myth and 'sociable' prosthetics}}, month = {October},year = {2009}, url = {https://www.swisswuff.ch/tech/?p=225}}