10 Mar 2013

Frederick B. Mills “A Phenomenological Approach to Psychoprosthetics”, summary

summary by Corry Shores
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[My own commentary is in brackets. All boldface and underlining is my own. Extra spacing between paragraphs follow the paragraph divisions in the original text.]

Frederick B. Mills

“A Phenomenological Approach to Psychoprosthetics”



Brief Summary

The integration of prosthetic devices into users’ bodies and activities can be seen in terms of Merleau-Ponty’s phenomenology of the body.

Abstract [Quoting]

The phenomenology of human embodiment can advance the practitioner’s understanding of the lived human body and in particular, what it means to incorporate a prosthetic device into one’s body. In order for a prosthesis to be incorporated into the lived body of the patient, the prosthesis must arguably be integrated into the body schema. This article uses the phenomenology of Maurice Merleau-Ponty and others to identify three of the necessary conditions of embodiment that determine the body schema: corporeal understanding, transparency and sensorimotor feedback. It then examines the structure of each of these conditions of embodiment and how they impact the lived body’s incorporation of prostheses and other artifacts. (Mills p.1)



The aim of Mills’ article is to “offer an interpretation of how some of the insights about embodiment contained in Maurice Merleau-Ponty’s work relates to the relatively new health science field of psychoprosthetics. These insights show the value of the phenomenological method to the understanding of human embodiment and introduce practitioners to the practice of phenomenology.” (1Ac)

Methodological considerations

Mills draws from Gallagher et al.’s definition of psychoprosthetics. Psychoprosthetics is “the study of ‘the psychological aspects of prosthetic use and of rehabilitative processes in those conditions that require the use of prosthetic devices’” (1Bd). Psychoprosthetics is concerned with “prosthetic technologies and the behavior and experience of the prosthesis user” (2Aa). Psychoprosthetics makes use of two complementary methodologies: 1) (object-orientation) evidence-based empirical research, which is thus mostly concerned with measurable outcomes; and 2) (subject-orientation) phenomenological efforts, normally concerned more with the qualitative lived experiences of the prosthesis user, and it “includes the systematic use of introspection, testimonials and questionnaires as research tools. Such phenomenological research, when applied to psychoprosthetics, is inter-subjective, empathetic, and focuses on what it is like to be the user of an artificial limb as he or she progresses through the rehabilitative process”. (2Aa.b)

Mills notes the importance of phenomenology in the work of Craig Murray, who  claims that clinical intervention that is informed by phenomenological research will make it more likely for prosthesis users to not give up until their device becomes integrated into their body schema; “until the prosthetic device is integrated into their bodies. This is because the qualitative experience of prosthesis use determines to a significant degree whether a prosthesis is really being progressively integrated into the user’s body. The work of Merleau-Ponty is relevant to this task because it helps us to systematically identify and study the basic experiential features of the incorporation of artifacts into the lived body.” (2Ab citing Murray 2008)

Merleau-Ponty does not ignore the importance of empirical research, and he deals with the question of what about human nature that opens it to both subjective and objective study. Merleau-Ponty breaks with the Cartesian substance dualism of mind and extension, which “poses an irresolvable problem of how the activities of the mind and body are nevertheless systematically correlated.” (2AD)

Merleau-Ponty thinks we need to “reach back to our lived experience prior to reflecting about our bodies as objects, we do not find ourselves divided into two separate worlds (a mind and a body) but as living, sensing and moving bodies.” (2Ba)

Our everyday experiences tell us that we do not normally separate mind and body, as for example when we see someone smile, we do not see it merely as flesh moving nor merely as an imperceptible emotion. “With this expressive nature of human behavior in mind, we can engage in a phenomenological investigation into the basic features of human embodiment and its extension in artifacts and in particular, prostheses.” (2Bb)

Basic features of embodiment

The body image and the body schema

Human embodiment’s structure includes both body image and body schema. There is no consensus on their meanings, but Mills will work through some distinctions and relations between them. (2Bc)

Our body image is the way we think we look to others. (2Bc)

Body image is also important for prosthesis integration, but this paper focuses more on body schema. (2Bd)

Shaun Gallagher defines body schema as ““a system of sensory-motor processes that constantly regulate posture | and movement – processes that function without reflective awareness or the necessity of perceptual monitoring” (Gallagher qt in Mills pp.2|3)

Mills broadens this definition. Body schema is the general idea of schema and body schemas are the system or plurality of schemas. Mills also broadens the concept of body schemas to include “processes of which we can be marginally and even focally aware.” (3Aa)

Body schemas are what allow us to engage skillfully with the world. Neuronal descriptions are not enough to describe this; we need to see how the structure and meaning of phenomenal experience correlates with neurophysiological processes in the brain. (3Ab)

Body image helps in the development of our body schema. (3Ac)

To elaborate the concept of body schema, Mills quotes Merleau-Ponty from Phenomenology of Perception [p.160-167]

A movement is learned when the body has understood it, that is, when it has incorporated it into its ‘world’, and to move one’s body is to aim at things through it; it is to allow oneself to respond to their call, which is made upon it independently of any representation. (Merleau-Ponty qtd in Mills 3Ac)

Mills gets three basic features of the body schema from the paragraph this quote comes from: 1) corporeal understanding, 2) transparency, and 3) sensory-motor feedback.

Corporeal understanding

Corporeal understanding is not reflexive because “unless we are learning a new skill, we do not normally represent a situation to ourselves prior to enacting the intended behavior; we merely aim at our purpose and the behavior unfolds in | its very enactment”. (3A-B) But our corporeal understanding is not reflexive either, because our behaviors are normally not mechanical responses to stimuli but instead “Objects call our attention because they have a certain value for us. We are active players in generating our behaviors.” (3Ba)

Corporeal is not something cognitive but is more like as Hubert Dreyfus calls it ‘know how’. We know how an action comes about in the context of a wider activity, like hitting the ‘h’ key while typing, even though we do not have an explicit visual map of the keyboard. (3Bb)

We need to reenact a behavior to recall it, because “corporeal understanding is activated at the lived body-world interface. At the body-world interface, we do not experience our bodies per se, as separate from the world; we experience our bodies as joined with and challenged by the world.” (3Bc)

Transparency (absence and presence)

Cognitive understanding requires that the part of the body that is perceptually and kinesthetically engages with the world be transparent to us. Drew Leder notes that insofar as our body brings some part of the world to presence, revealing it to us, the part of the body that does the revealing withdraws from our view, like our our eyes are absence from our field of vision. (3Bc)

Mills quotes Merleau-Ponty to elaborate [Phenomenology of Perception p.104]:

I observe external objects with my body, I handle them, examine them, walk round them, but my body itself is a thing which I do not observe; in order to be able to do so, I should need the use of a second body which itself would be unobservable. (3Bd)

Transparency is a part of all our kinetic and perceptual behaviors. (3-4)

Michael Polanyi notes how our the motile and perceptive parts of our body recede and in a sense become transparent; Drew Leder “calls this type of absence focal disappearance”. (4Aa)

Also, according to Leder, we experience the background disappearance of our body; through most of the day we have just a marginal awareness of it. Mills will use ‘transparency’ to refer to both kinds of phenomenal absence. (4Ab)

Intentionality is thinking’s manner of being directed towards objects. For Merleau-Ponty, it is the whole lived embodied person who does the thinking, perceiving and behaving.

As living bodies, we are both perceptually and kinesthetically directed towards and engaged with the world. Merleau-Ponty conceptualizes the ways in which we are directed towards our world as rays of intentionality projecting out of the body schema. These rays constitute our many purposes and invest our surroundings with the meaning of possible behaviors. The door is the way out of the room. The keyboard is the potential to enter data. The light switch is the potential to turn the lights on or off. The road is the way out of the neighborhood. The rays of intentionality are correlated with a network of utilitarian relationships between objects in the world. Merleau-Ponty refers to the totality of these rays as an “arc of intentionality” (4Ac)

Normally much in our arc of intentionality remains below our thematic awareness until something brings them into focus. (4A.B)

Things can come into focus for a variety of reasons, depending on the context. (4B.ab)

Changes of thematic awareness can be like Gestalt figure/ground shifts. (4B.b)

Sensorimotor feedback

From the physiological perspective, “sensations are neural events and sensorimotor feedback is a dynamic relationship between the adaptive body and environmental stimuli”; but from the phenomenal perspective “sensations are qualitative experiences.” Mills will focus on the phenomenal aspect. (4B.c)

Sensorimotor feedback can be marginal and focal and involve more than one perceptual Gestalt at a time. (4D) This helps us attend to multiple tasks at one time. (5Aa)

Incorporation of artifacts into the lived body

On these bases will will conceptualize the incorporation of artifacts, such as prosthetic devices, into the lived body.This requires a modification of the three basic features of embodiment. (5Ab)

Incorporation of artifacts involves integrating them into our body schema.

When an artifact is integrated into the body schema such that it modifies the corporeal understanding, the body and artifact merge in such a way that together they interface with the world to generate behaviors that are neither reflexive nor conceptually guided but rather skillful or habitual. This means that the body schema comes to include the artifact in its arc of intentionality. (5Abc)

Incorporation also involves a change in the absence presence dynamic where the artifact becomes absent or transparent.

Ideally the prosthesis can become a part of the body from which a worldly gestalt becomes present and a skillful or habitual behavior becomes possible. Such integration can occur when sensorimotor feedback appears to come from the interface between body-artifact as a unified whole and the world rather than the interface between the body and the artifact. (5Ac)

Examples of the embodiment of artifacts

Merleau-Ponty uses the examples of the walking stick and the typewriter. [At the end of this entry we look at the examples and the passages they come from.] Mills quotes Merleau-Ponty [Phenomenology of Perception 165-166]

The blind man’s stick has ceased to be an object for him, and is no longer perceived for itself; its point has become an area of sensitivity, extending the scope and active radius of touch, and providing a parallel to sight. In the exploration of things, the length of the stick does not enter expressly as a middle term: the blind man is rather aware of it through the position of objects [p.165 | p.166] than of the position of objects through it. (5Ba)

So the walking stick eventually is incorporated into the arc of intentionality and becomes like an extension of her body.

The user literally extends her reach, the stick being lived as part of the extended arm. The stick becomes transparent because the blind person is not focused on her grasp of the walking stick; she is directed towards the ground through the hand-stick combination. Sensorimotor feedback is experienced not as a relation between the hand and movements of the stick but rather as an experience of the texture and location of the ground and other items through the stick as if it were an extension of her arm. (5Bb)

Mills also quotes Merleau-Ponty’s typewriter example [Phenomenology of Perception 166-167]

It is possible to know how to type without being able to say where the letters which make the words are to be found on the banks of keys. To know how to type is not, then, to know the place of each letter among the keys, nor even to have acquired a conditioned reflex for each one, which is set in motion by the letter as it comes before our eye. If habit is neither a form of knowledge nor an involuntary action, what then is it? It is knowledge in the hands, which is forthcoming only when bodily effort is made, and cannot be formulated in detachment from that effort. The subject knows where the letters are on the typewriter as we know where one of our limbs is…. When the typist performs the necessary movements on the typewriter, these movements are governed by an intention, but the intention does not posit the keys as objective locations. It is literally true that the subject who learns to type incorporates the key-bank space into his bodily space. (5Bb.c)

The key, the finger, and other aspects of the body’s positioning and behavior fall into the background. (5Bc)

The corporeal understanding of the skilled typist is not reflexive, because the keys are not stimuli causing her fingers to move. And the typing does not involve representation, because the typist does not make use of a mental model representing the keyboard. “The corporeal understanding is in the hands.”  (5Bc.d)

Embodiment of prosthetic devices

So the incorporation of prosthetic devices requires a modification in our corporeal understanding, transparency, and sensorimotor feedback. (5-6) Mills draws from Craig Murray’s empirical studies of prosthetic incorporations.

For there to be transparency, the device must be affixed properly so that no pain or discomfort is felt, for otherwise it will be noticed rather than disappear from awareness. Practice is as well critical for attaining transparency. [Following first quotes Mills, then has Mill’s quote of Murray 2004]

Murray notes that some respondents testify that with practice, walking starts to become natural again:

Walking becomes pretty intuitive after the age of three or four; you don’t think about it, you just do it. Now, I do have to think occasionally, such as when I stand up from a chair. I have to think which foot, is that foot in the right position, is it going to hit anything? You do still have to check for things like that. Occasionally, I’ll get it trapped under a chair as I stand up. So a couple of times it brings it back to you that you have a problem there. But once moving, in general, it’s pretty much a matter of well I want to go from here to there, and I just walk. It’s intuitive now. (6Abc)

Mills continues [again first Mills then Murray 2004]

The prosthesis, in one report, became so transparent, that the user got up from bed without realizing that the artificial limb was not on: “I fell on the floor, landing on the distal end of the stump. It was a very frightening thing. Scary. It hurt like hell, and I stayed off it for about a week. So I guess I have reached a point where I am capable of such foolish acts as that and forget my leg was not on.” (6Ad)

Incorporation could be more likely if sensorimotor feedback occurs “at the interface of the prosthesis and the environment”. (6Ad) Mills notes [second is quote from Murray 2004]

One user in the Murray study reported: “I do sense it [the ground] with the prosthesis on. It is a general awareness of the ground. As I walk, I can feel my heel land, and the foot move forward to the toes”. (6Ba)

There are technologies that can make the feedback appear to come from the environment.

For example, prosthetics fixed to bones rather than fitting in sockets tend to give better feedback. [citing Hagberg et al.]

For example, the sensorimotor feedback provided by boneanchored (osseointegrated) prostheses (OI), osseoperception, seems to be more vivid and detailed than that attained by socket technology. In one study, several patients reported more control over their artificial limb (than with a socket style prosthesis) and the ability to identify the material of the surface they are walking on. Other users report that the osseointegrated prosthesis feels more like a part of the body than did the socket prosthesis. (6Bb)

Another technique for enhancing sensorimotor feedback is targeted re-innervation, which “improves the communication of the surface of the prosthesis with intact nerves on the residual limb.” (6Bb) [When a limb is amputated, it seems in these cases that the nerves of that limb are removed and reattached to the remaining limb nerve channels, so that sensations normally given in the limb are still givable through these nerves. Then, sensors in the prosthetic limb create signals that stimulate the attached nerves so that the user feels as if the sensation is coming from within the prosthetic device.]

There are a variety of technologies that seek to improve the communication of the surface of the prosthesis with intact nerves on the residual limb to improve sensorimotor feedback. One of these strategies is targeted re-innervation. In a 2010 study conducted at the Rehabilitation Institute of Chicago and led by Paul D. Marasco, an artificial sense of tactile sensation was created for a prosthetic limb so it felt, to the user, as though sensations were coming from the prosthesis and not merely mediated by the prosthesis. Here is how it works. Sensors are placed on the artificial hand. These sensors send a message to a robotic device that is located on the residual limb in proximity to areas sensitized by the re-innervated nerves. The robotic device responds to the sensor information by stimulating “surgically redirected cutaneous sensory nerves... that once served the lost limb”. I want to emphasize that Marasco used both evidence-based medicine and phenomenology. In particular, he made use of questionnaires and testimony as well as temperature changes in the residual limb. He found that the illusion that sensations were coming from the prosthesis were vivid. Marasco suggests that “this may help amputees to more effectively incorporate an artificial limb into their self image, providing the possibility that a prosthesis becomes not only a tool, but also an integrated body part”. If we couple this technology with recent advances in the kinesthetic response of prosthetic devices, users may benefit even more from enhanced sensorimotor feedback. It is likely that the more such devices mimic organic limbs and provide sensorimotor feedback, the more a corporeal understanding and a natural feel can be achieved. [Mills 6Bb citing Marasco et al.]


Not all prosthesis users attain transparency. “However, in those cases where integration is the goal, the insights of Merleau-Ponty on the lived body help us to understand what it means for a prosthetic device to be incorporated into a patient’s lived body.” (6Bd)

Mills concludes “Those rehabilitative strategies that begin to make the prosthesis more transparent to the user; provide finer grained sensorimotor feedback as coming from the (body-prosthesis) – world interface; and restore increasingly more skillful functionality are likely to achieve the maximal prosthetic incorporation.”  (7Ab)

Frederick B. Mills. “A Phenomenological Approach to Psychoprosthetics.” Disability & Rehabilitation, 2012; Early Online: 1–7 © 2012 Informa UK, Ltd. ISSN 0963-8288 print/ISSN 1464-5165 online

Gallagher P, Desmond D, MacLachlan M. Psychoprosthetics: an introduction. In: Gallagher P, Desmond D, MacLachlan M, editors. Psychoprosthetics. London: Springer-Verlag Limited; 2008. pp 1–10.

Gallagher S. How the body shapes the mind. New York: Oxford University Press; 2005.]

Hagberg K, Häggström E, Jönsson S, Rydevik B, Brånemark R. Osseoperception and osseointegrated prosthetic limbs. In: Gallagher P, Desmond D, MacLachlan M, editors. Psychoprosthetics. London: Springer-Verlag Limited; 2008. pp 131–140.

Leder D. The absent body. Chicago: The University of Chicago Press; 1990.

Marasco PD, Kim K, Colgate JE, Peshkin MA, Kuiken TA. Robotic touch shifts perception of embodiment to a prosthesis in targeted reinnervation amputees. Published by Oxford University Press on behalf of the Guarantors of Brain; 2011, January 20.

Merleau-Ponty, Maurice. Phenomenology of Perception. Transl. Colin Smith. London/New York: Routledge, 1958.

Murray CD. An interpretative phenomenological analysis of the embodiment of artificial limbs. Disabil Rehabil 2004;26:963–973. 3.

Murray CD. Embodiment and prosthetics. In: Gallagher P, Desmond D, MacLachlan M, editors. Psychoprosthetics. London: Springer-Verlag Limited; 2008. pp 119–129.

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