Saturday, June 03, 2017

Ownership and agency in a predictive brain, implications for manual therapy


Recently I stumbled upon a lovely article in The Scientist, Understanding Body Ownership and Agency

It suggests there are several "selves" within each of us that integrate into a singular seamless "self". 
It's easy enough to manipulate the sense of ownership in several ways - research on kinaesthetic body illusions such as mirror therapy, rubber hand, are discussed. Brain interface prosthetics for amputees are mentioned. 

A slide I made using definitions from the article

The article proposes that agency and ownership, while slightly different, are integrated into one another, and are interdependent. 

"...recent research has sought to understand how body ownership might have developed through the sum of agency experiences that we accrue throughout our life. What we perceive as our body is not only what looks like our body, but what we typically have conscious control over. This control is asserted by learned associations between our muscular movements and the sensory feedback we perceive when performing an action—the so-called “action effects.” 

So, agency precedes ownership, sounds like... we learn our arm is part of "us" i.e., "self", by realizing we can control its movement. Bring food to mouth. Etcetera.

The two are slightly separable concepts though: Ehrsson's virtual body part research is mentioned.

In 2012, Ehrsson, along with his then graduate student Andreas Kalckert, designed a rubber-gloved wooden model hand to make finger movements that were either linked by a wooden rod to (and thus synchronous with) movements of the participant’s own hidden hand, or detached and controlled independently by the experimenter.16 Initiation of synchronous movements by the participant elicited a strong sense of ownership and agency over the model hand; linked, synchronous movements initiated by the experimenter (passive movements) abolished the sense of agency, while the sense of ownership remained intact. Conversely, when the experimenters rotated the robotic hand by 180 degrees—putting it in an anatomically implausible position, with the fingers facing toward the body—participants maintained a sense of agency, but not of ownership.

(I'll never forget the drama involved in Ehrsson's set up, where he induced the illusion of ownership of a rubber hand, then attacks the rubber hand with a hammer, or a knife or something, and measured all the autonomic reaction in the subject.)

The paper brings up some definitions:

"Based on theoretical ideas of 19th century physician and physicist Hermann von Helmholtz, German scientists Erich von Holst and Horst Mittelstaedt demonstrated the reafference principle in 1950 to distinguish between self-generated movements and external perturbations. Any time we move, we generate a motor command (efference) to control the muscles. At the same time, we also generate a prediction—based on prior experience of the sensation resulting from the movement—termed the efference copy. The actual movement-related sensory input, which comes from receptors in the muscle and skin, is referred to as reafference. Any difference between the two signals (reafference and efference copy) is the result of environmental input, which is termed exafference. Understanding errors that may occur within this system is probably central to understanding problems in agency and ownership perception."

Hurray! Words!
I wondered how manual therapy might be involved. 

.... And I speculate: 

 May 1, Understanding Body Ownership and Agency,  2017, The Scientist

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