Disowning Limbs in The Healthy Brain

Question 1

Intro

Answer 1

Possible to induce ownership over fake limbs and virtual bodies using multisensory illusions.

However, unresolved question remains relating to whether or not we disown our own limbs/bodies when embodying a new limb/body…

Question 2

Gusterman

Answer 2

Used VR and real time video to change the PS visual perpective to that of a pair of cameras placed 2m behind body.

• Experimenter stroked real and illusory chest sync and async
• Creates illusory experience that one’s body is located 2m behind real body and that the (camera) rod is directly causing the felt touch.
• 2 basic experiences: 1) illusory body and 2) illusory self-location
• Measured SCR [measure of disownership] and Questionaire (asked how much they felt like they were located at the camera and at their body)
• Found reduced SCR when own body threatened after sync stroking
• No SCR difference between sync and async when another body threatened
• Demonstrate that ownership of ‘new’ body entails losing the ‘old one. Rather than experiencing both simultaenously, this OOBE involves one united bodily self.

Question 3

Barnsley (2011)

Answer 3

Applied histamine to skeen on both arms
- RHI elicited every 3 min for 20s

• Found that the whhheal was bigger on the experimental arm during the illusion than it was on the control arm during the illusion / or on either arm during the control condition
• Vividness of illusion correlated with size of whheal
• Authors claim this increased whheaal represents rejection (disownership) of the stimulated limb, supporting the notion that limbs can be disowned

Question 4

Moseley (2008)

Answer 4

RHI but used temperature os proxy measurement of ownership
The stimulated limb experienced a drop in temperature which was related to the strength of the illusion
- Only the stimulated hand cools (not the other hand, or the foot)

Question 5

Rohde (2013)

Answer 5

• Used robots (perfect temporal synchrony) stimulate hands
• Also used more accurate temperature measure
• They DID NOT find temperature drop

Question 6

Salomon et al (2013)

Answer 6

FBI, HMD where PS veiwed virtual avatar (OOBE)
- Sync/Async robotic stroking on the arm and back of the leg

• ## Found OOBE = sig. body temperature drop

Question 7

Preston (2013)

Answer 7

PS completed RHI but with questions that probed disownership

• Found synchrony modulated the degree of disownership (as well as illusion score)
• However, disownership score NOT related to illusion strength or PPD
• Therefore, lack of support for disownership

Question 8

Ehrsson (2009)

Answer 8

Double rubber hand illusion - 2 rubber hands stroked
SCR response indicated embodiment of both hands
This suggests our body schema is malleable enough to include more than one limbs

Question 9

Newport and Gilpin (2011)

Answer 9

Disappearing Hand Trick
While hovering the hands above a tabletop surface (inside of the MIRAGE multisensory illusion box), participants enjoy a real-time video of their hands, that through a covert process of sensory adaptation and disintegration, visually appear to be closer together than they physically are.

When the image of the hand is faded out and the participant is asked to reach for it, it is not where he (visually) expects it to be.

Individuals report that from this experience, the hand feels as though it is no longer part of the body (nor that it belongs to them), that it feels cooler than normal, and that they do not know its location.

Suggests that yes, you can disown limbs in the healthy brain.