The year 2018 was interesting in relation to the rubber hand illusion subject.
I had participated in an extensive interview study regarding embodiment just a year before [link]. Then, I had been identified as a prosthesis "super user" [link] - these people wanted to investigate my type of "embodiment" through fMRI, but we quickly identified my prosthetic arm design (not my brain) as the key aspect regarding the question of why I have a prosthesis that I can actually use rather than just pose with as so many others. My own view here clearly is that if you are after embodiment, you have to go all Sherlock Holmes, you have to go all forensic, all CSI and all crime mystery: and as in "cherchez la femme" when looking for a motive in a crime, it is "cherchez le bras" when studying embodiment: for all issues that center around prosthetic use, go for the core physical aspects first. There are extremely bad things that may, can, and will happen if you do not make that your real first priority. The "rubber hand illusion" is an extreme variation of body ownership of a rubber hand that does not even touch a person and still that person thinks they are being touched if that rubber hand is touched. The illusion to make an amputee believe they embody or bodily own a prosthetic hand is quite different. But both pose risks, whereas the risk that an amputee faces when getting a prosthetic arm that is integrated into his body image has not been considered yet. My slightly experience based consideration proposes that the body image is tyrannically governed, for good and for bad, and if the prosthetic body part - already starting with bad cards, body image wise - craps out, and it always does so far too often, then it draws the hot red angry ire, the depressed disappointment, the falling apart of the cyborg body, of the amputee - and definitely not the cool "oh a neutral object just disintegrated" that one will wish for from a societal, insurance or repair view. The integration into a body image brings with it that the device becomes subject to totally tyranically governed bodies. When it is difficult enough to make any device ready for real world usage, making it ready to survive tyrannies of that nature will be even harder. I proposed an unforgiving approach to failure testing in a recent paper (link) but I cannot say that paper has been greeted with any enthusiasm by the industry that actually builds prosthetic arm components. Because they get to directly face the anger, hate, and rejection of all the users that they had not informed well of just how fragile their prosthetic arm parts really are (link), and they are in absolutely no position to technically improve these parts. So, manufacturers go into hiding. They do not want many users - they want users that buy and do not complain. The last thing they need is a hard bright unforgiving look into just how bad their engineering is. Every non-user, every rejector, should be cautiously left alone, not recruited to wear a prosthesis - because the risk is considerable (link). Researchers currently have the problem that amputees run away, everywhere (link), also because we are continously treated as mentally incompetent. So in essence, we are a group of people that increasingly realizes the extent to which we are being fooled, being had, told stories, and increasingly, we are getting critical. Potential rubber hand illusion switches, dragged to market to be soldered into prosthetic arms, if ever they are a medical treatment or a part thereof, will have negative effects as well: what are these? What do we know about deeply problematic aspects of bodily ownership? I had been invited to talk about that aspect for a group of people interested in robotic control and user interfaces, on December 7th 2018, in Mannheim (Germany). The presentation that I gave now is typed out here in more detail for further reference.
Rubber hand illusion is an idea that, by and large, was somehow transformed into multi-sensory rubber hand illusion, and they now want to put it into prosthetic arms to make users believe the prosthesis belongs to their bodies.
With that, rubber hand illusion goes to market.
This is not really that fascinating. While I am not interested in prosthetic arms because I find the field fascinating, I have been drawn into the field due to circumstances. And as much as you feel that I am locked into this constraint space of shared idiocies, dreams, hopes and failing hardware together with you, in some type of brotherhood by bad fate, you may also realize you are locked into this with me, as consequence of bad fate. Those then are also circumstances. As I deal with it, you may also have to find a way. If you think that is uncomfortable, send me a mail, so we may talk about uncomfortable a bit.
The ultimate consquence of this piece of reflection is not at all bad, however. We will see just how too much "ownership" has bad aspects as well. It risks to slip prosthetic hands into a domain where it is subject to the most vicious decision making that there is: tyrannic and wilful, impulsive and emotional decision making within one's own very personal domain of body or body image with owned body part dependent urgencies and requirements. To withstand these storms, a prosthetic arm has to withstand not only the physical requirements of real life use (which it normally does not to a degree that will make your jaw drop), it also has to be acknowledged in that capacity by manufacturers and care-givers, emergency teams or repair units, where none of similarly urgencies are currently provided.
To even reach a level of "tool", to be useful enough to be accepted as technical solution (not as embodied "owned" limb), a typical prosthetic arm may have to undergo a most serious metamorphosis, from commercial parts (link)(link) to tuned and optimized parts (link). If you are in R&D and want to do something good in support of arm amputees, it may be relevant to address actual issues such as failing devices or phantom pain (link), before going all out on a limb and drag ill-defined concepts to a domain where they may wreck more than they really help.