Rubber Hand Illusion

Question 1

Intro

Answer 1

The experience of owning a body is taken for granted. However, it in unclear how we dissociate our own bodies, from the bodies of other and the objects around us.

Question 2

RHI Intro

Answer 2

RHI used to investigate the factors that contribute to body ownership. In the original paradigm, a fake rubber hand placed next/on top of real hand (hidden from view).
If real and rubber hand are stroked syncronously, participants tend to feel ownership over the fake rubber hand.
Thus, tight correlation of multisensory information seems to be a contributing factor to the sense of body ownership . This is an example of bottom-up processing that influences sense of body ownership.

Question 3

DVs of RHI

Answer 3

Illusory ownership is measured in 3 ways. 1) Questionaire itmes assessing subjective experience ownership 2) Proprioceptive drift assesses the extent to which the felt position of the real hand has shifted towards the fake hand - Implicit measure of ownership 3) SCR - Experimentor ‘threatens’ the rubber hand and measures the brief evoked increase in skin conductance to provide objective evidence for the illusion - if ownership has occured, SCR tends to be higher. SCR is seen as a reliable index of body ownership (Ehrsson et al, 2012).

Question 4

This essay will.

Answer 4

As well as bottom-up processes, top-down processes also influence body ownership. This essay will examine the relative importance of such factors

Question 5

Armel & Ramachandram (2003)

Answer 5

…compared the strength of the illusion induced over a table-top to over a rubber hand. They used SCR and questionaire. If PS can embody a table, it suggests that bottom-up factors override top-down factors of body ownership. They manipulated the synchrony of visuo-tactile stimulation, such that the control condition was the table being asynchonously stroked

• SCR and questionaire indicated that PS could embody the table top during sync condition, highlighing the power of bottom up factors in influencing ownershio, despite top-down knowledge that a table is not part of one’s body being present.
• However, the embodiment of the table top was less than the embodiment of a rubber hand, suggesting that the top-down expectation of what a body part shoudl look like still plays a significant role.

Question 6

Guterstam et al (2013)

Answer 6

Invisible Hand Illusion
Had experimentor stroke an ‘invisable hand’ sync and async with their real hand
Measured Questionarie, SCR, PPD
Found that duirng the sync condition, participants had the experience of owning an invisable hand

Demonstrates that that visual information that provides clear evidence that a hand is not present at a specific location, as well as prior knowledge regarding what a hand looks like, can be overridden by specific spatiotemporal patterns of visuotactile signals.

Found this pattern of ownership was associated with increased functional connectivity between intraparietal sulcus and ventral premotor areas - both areas known to be important for multisensory integration.

Question 7

Tsakiris & Haggard (2005)

Answer 7

• Had a condition where rubber hand was rotated such that is was incongruent with expected body position
• Measured Proprioceptive Drifta as index for illusion strength
• Only during congruent posture condition was there a normal illusory effect
• This suggests there the synchronous of vision and touch may be necessary but not sufficient for body ownership
• Limitation: Only used Proprioceptive Drift as DV (not SCR, not questionnaire). Therefore lack of convergence using different modalities

Question 8

Tsakiris (2010)

Answer 8

• 5 hand stimuli were used, with decreasing levels of corperality
• Measured PPD and Questionnaires
• Only when block of wood looked sufficiently like a hand did the illusion take place - synchrony of vision and touch again, not sufficient
• Limitation: Rubber hand did not just differ in corporeality, but also in texture
• This difference may have resulted in significant differences in the perceived sensory quality of the tactile stimulation delivered on the viewed objects, and as a result they could have affected the experience of ownership

Question 9

Haans (2008)

Answer 9

This study manipulated texture during the RHI …suggests that texture of an object does not effect ownership

Question 10

Lloyd (2007)

Answer 10

Rubber hand needs to be near to the real hand…

- distances greater than 27.5 cm lead to a significant reduction in illusion strength.

Question 11

Zopf et al (2010)

Answer 11

Found that there was no reduction in RHI strength with distances up to 45cm

Question 12

Cadieux (2011)

Answer 12

The difference with Lloyd may be because Lloyd’s distance manipulation crossed the midline of the body, which has previously been found to abolish the PD in RHI

Question 13

Ma & Hommel (2018)

Answer 13

Biased PS to think in a convergent or divergent manor

• convergent thinking (Remote Associates) task or divergent-thinking (Alternate Uses) task
• questionnaire + drift
• Found RHI strength increased when divergent
• Because divergent thinking decreases top-down constraints, thus promoting a more flexible body schema