Tastevin was testing perception of touch and finger position when he noticed that people often mistook a plastic finger protruding from underneath a cloth near their hand as their real finger. Over the next 40 years, research focused on the senses of touch and limb position , but little, if any, focus was given to mental representations of the body other than case studies of neurological disorders.
Fast-forward to , when Princeton University cognitive scientist Matthew Botvinick headed a study on an illusion similar to the one Tastevin observed to evaluate body ownership. Researchers placed a rubber arm on top of the table in alignment with the real arm below. Subjects reported feeling as if the rubber hand were their own after synchronous but not asynchronous stroking. This rubber-hand illusion RHI suggests that the sense of self is highly malleable; the perceived location of the arm as estimated from the senses of touch and of limb position known as proprioception is superseded by visual input, as this sense is often more reliable.
Some have measured physiological responses following threats to the rubber arm to objectively test if that limb is perceived as a part of the body.
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In , Vilayanur Ramachandran of the University of California, San Diego, and Carrie Armel of Stanford University observed an increase in sweat production, known as skin conductive response SCR , when they bent a finger on the rubber hand into a position that would normally be excruciatingly painful. Illusions of embodiment can be induced in ways other than discordant visual-tactile stimuli.
Receptors in skeletal muscle known as muscle spindles make a large contribution to our sense of proprioception. Moseley and colleagues wondered if muscle spindles might also contribute to the sense of ownership. The experimenters found that when they synchronously moved the real index finger and the rubber finger, the participants reported feeling that the fake finger was embodied, suggesting that input from muscle spindles in conjunction with vision is sufficient to generate ownership.
Knowing what we now do about body ownership, can we help amputees fully embrace their prosthetic limbs? In the mids, researchers at the Toho University School of Medicine in Tokyo, Japan, trained macaques to use a rake to retrieve objects and found that neurons responsive to touch stimuli from the hand and to visual input now also respond to the rake when it was in use.
As a work-around, researchers have begun to use electrical stimulation of the brain regions thought to be involved in representing the body to mimic the effects of stroking a real limb. Last year, working with two patients undergoing brain surgery for epilepsy, Kelly Collins of the University of Washington and colleagues stimulated the region of the somatosensory cortex corresponding to one hand while touching a rubber hand visible to the participants.
Neuropsychology of the Sense of Agency
This study provides hope that a similar procedure could help train amputees to embody their prosthetic limbs. To date, effects of the RHI on pain reduction are equivocal, but a couple of studies suggest that variations of the illusion could have potential, as they generate stronger, more holistic feelings of ownership. The researchers stroked either the intact hand of a complete mannequin or the stump and the area below the stump of an amputated mannequin, while at the same time stroking the stump of the participants. They found that the illusion reduced pain ratings by 37 percent in this cohort.
A better understanding of how body ownership is encoded in the brain could also one day help treat patients with more-extreme body illusions, such as the brain lesion patient who has lost control of her left hand or the defendant who insists he did not fire the gun. Damage in multisensory areas of the brain—particularly the transition between the parietal and the temporal cortex, the so-called temporo-parietal junction, and parts of the medial frontal cortex 11 —may result in an object being incorrectly embodied or in the disembodiment of a limb or even the whole body, as in the case of patients having out-of-body experiences.
We have control when we reach for a glass of water, when we kick a football, and when we put pen to paper. 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 to distinguish between self-generated movements and external perturbations.
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Any time we move, we generate a motor command efference to control the muscles. In the s, facilitated communication, or supported typing, was promoted as a teaching strategy for helping people with autism communicate with the wider world. But the striking thing was that most of the facilitators sincerely believed that they were not the agents of these actions.
Free will is not something we have, so much as something we feel. These observations point to a fundamental paradox about consciousness.
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Why have it? Contrary to what many people believe, I think agency is only relevant to what happens after we act — when we try to justify and explain ourselves to each other.
There are a few hints that support this view. But we have to learn to interpret such feelings, and what other people tell us can alter the way we respond. When doing hard mental work, we have a strong sense of making an effort. In the same way we learn to associate certain experiences of action with a sense of agency. And it is these kinds of action that we feel responsible for.
T he bond between agency and mutual accountability goes back at least as far as BCE. The Greek philosophers, Epicurus and the Stoics, wanted to defend the idea of free will despite believing the universe to be pre-determined by the laws of nature. Free will has two fundamental features, they said.
Furthermore, Epicurus believed that we acquire this sense of responsibility via the praise and blame we received from others. By listening to our peers and elders, we become attuned to our capacity to effect change in the world. Our conscious experience is what enables us to pick up these lessons.
For example, many children are reminded to think before they act, lest they regret it. In another time and place Ben might not get off so lightly for inadvertently kicking Freya. As a result, people are frequently held responsible for their wrongdoings , even when they were the result of an accident or error. Intentionality is impossible to grasp, and therefore largely irrelevant.
Similarly, among the Mopan Maya of Belize and Guatemala, children and adults alike are punished according to the outcome of their actions. Theoretical and Neuropsychological Evidence. From Perception to Selfknowledge. Functional and Dysfunctional Mechanisms. Subject Index.
Bibliografische Informationen. Section I Cognition Consciousness and Agency.
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