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(this part will be for the body schema page)

Extended Body Schema

The idea of the extended body schema is that, aside from the proprioceptive, visual, and sensory components that contribute to making a mental conception of one's body, the same processes that contribute to a body schema are also able to incorporate external objects into the mental conception of one's body. Part philosophical and part neuroscience, this concept builds upon the ideas of plasticity and adaptation to attempt to answer the question of where the body schema ends.

There is debate as to whether this concept truly exists, with one side arguing that the body schema does not extend past the body and the other side believing otherwise.

Supporting Arguments

The perspective shared by those who agree with the theory of the extended body schema follow reasoning in line with such that supports theories on tool use.

In some studies, attempts at understanding tool assimilation are used to argue for the existence of the extended body schema. In an experiment involving the use and interaction with wool objects, subjects were tested on their ability to perceive afterimages of wool objects in varying contexts. Subjects accustomed their eyes to a dark room and then were shown a brief (1 millisecond) flash of light, intending to produce an afterimage effect of their arms which they held out in front of them during the experiment. Moving an arm afterwards would make the afterimage "fade" or disappear as it moved, thus indicating that the feature (the arm) was being tracked and integrated into the person's body schema. To test integration of the meaningless wool objects, subjects experienced four different contexts.

1. Subjects held the wool objects in each hand and one hand (the active hand) would move, still holding the object (the active object).
2. Using the active hand, the active wool object would be dropped once an afterimage was perceived.
3. Using the active hand, one would grab the active wool object once an afterimage was perceived.
4. The subjects were to hold onto a mechanical device which held the wool object. Once an afterimage was perceived, a subject's active hand would cause the mechanical device to drop the wool object.

In all situations but the fourth, the subjects experienced the same "fading" effect as they did with their arm alone. This would thus indicate that the wool objects had been integrated into their body schema and contributes support towards the idea of the body's using proprioceptive and visual elements to create an extended body schema. The mechanical device acted as an intermediate between the subject and the active object, and the subjects' failure to detect an afterimage in that context indicates that this concept of extension is limited to being sensitive to only what the body is directly in contact with.

Dissenting Arguments

The alternate perspective is that the body is the limit of any sort of body schema.

An example of this division is found in a study and discussion on personal and extrapersonal attention, where personal relates to the body's sense of itself (the body schema) and extrapersonal relates to all external of such. Some research supports the claim that these two categories are purely distinct and do not intermingle, contrary to what the extended body schema theory describes. Evidence for such is primarily found in subjects with unilateral neglect, such as in the case of E.D.S., who was a middle-aged man with right hemisphere brain damage. When he was tested for hemispatial neglect using traditional measures such as sentence reading and cancellation tests, E.D.S. showed few signs and upon later examination showed no signs whatsoever, leading doctors to believe he was normal. However, he constantly had issues with physical therapy because he would claim to not be able to see his left leg; upon further examination, E.D.S. was known to have a particular type of hemispatial neglect that only affected the perception of his body. The motor function of the left side of his body was negatively affected though not totally compromised, yet when attempting tasks such as shaving, he would invariably not shave the left side of his face. This led some researchers to believe that there is a distinction between personal and extrapersonal neglect, which would thus reflect a similar distinction with body schema itself.

Body Image (medicine)

Body image is a neurological and medical term, often used in the context of describing a person's cognitive perception of their own body. The concept was introduced by Austrian neuropsychiatrist and psychoanalyst Paul Schilder whose book, The Image and Appearance of the Human Body, was first published in 1935. This concept has a relation to the idea of self-awareness yet is more specific in its defined limits.

Body image and Extended Body Schema

In 1996, a patient known as C.B. experienced a stroke in the right hemisphere of her brain, causing hemispatial neglect on her left side. She wore rings on her left hand yet post-stroke was unable to recognize the rings as being hers so long as they were on her left hand. She also could not recognize her left hand as being hers whatsoever, claiming it belonged to her doctor. It was not until the rings were either placed in front of her or on her right hand that she was able to recall her ownership of the rings. C.B. no longer experienced this effect after she recovered from her stroke. Aglioti et al. wrote that C.B.’s experience could lend credence towards an idea of an “extended body schema”, which involves both a person’s body and the items which a person has made an attachment with. Given changes in nomenclature, a more modern term would be “extended body image”. In this same paper and research, there is a reference to a woman who had similar brain damage yet could only recognize her wedding ring when it was worn on her body, also indicating a necessary relation between flesh and extracorporeal objects to satisfy body recognition and self-perception. However, the researchers did not substantiate this anecdote with data.

Concept as found in other species

Research into whether animals have a degree of self-awareness shows that particular species also contain ideas of body image. Some Magpie, for example, were shown to have this perception through experiments using the mirror test and the mark test. A majority of magpies in the study showed behavior reflecting their perceptions of body image, such as making systematic movements that indicate their testing the contingency of the reflection’s movements to their own to verify that the reflection is theirs. When a part of their body was highlighted with a mark, most birds would attempt to reach said mark on their own body, thus recognizing the reflection as their own and acting based on the information their reflection provided. These behaviors were clearly dependent on the mirror’s presence, as when the mirror was replaced by a gray plate of the same dimensions, no self-behaviors were noted. Thus the magpies in this study showed to have an idea of their body image.

This finding in particular was significant not only for its contribution to the idea that a species’ perception of body image was a convergent feature, but also for its support for the notion that a neocortex is not the necessary threshold for self-recognition, as was once thought based on studies on primarily mammals.