Extending Body Space in Immersive Virtual Reality: A Very Long Arm Illusion

In the paper

“The estimated probabilities of the score being at least 4 are 0.86, 0.78, 0.66 and 0.52 respectively.”

In the paper

“The median of these 30 angle estimates is 45.6°, and the median of the corresponding 30 standard errors is 0.76° with interquartile range 0.59°.”

In the paper

“The only other response that shows a trend is Q7 (the feeling of being harmed) where the median is greater in the congruent condition”

In the paper

“For elongation 1 to 3 there are always at least 7 out of 10 participants with scores of at least 4. This declines to 4 out of 10 for elongation 4.”

In the paper

“The (two-sided) significance levels are for C2 P = 0.037, for C3 P = 0.012, and for C4 P = 0.169.”

• Also stated in: § The Effect of Elongation · plain

  “AngleAfter is significantly greater than AngleBefore for C2 (P = 0.04) and C3 (P = 0.01) but not for C4 (P = 0.17), Wilcoxon matched-pairs signed-rank tests.”

In the paper

“However, there is no difference in median scores for the ownership question, and the median scores are both high (4 out of a maximum of 5).”

In the paper

“and a defensive withdrawal movement evoked by a threat to the virtual arm near the distant hand position.”

In the paper

“Questionnaire scores and defensive withdrawal movements in response to a threat showed that the overall level of ownership was high in both C1 and I, and there was no significant difference between these conditions.”

In the paper

“However, the mean Saw Time dispersion is greater than the mean Control Time dispersion for each group I and C1 separately (bearing in mind that the significance levels are two-tailed) and for the two groups combined.”

In the paper

“However, responses to Q1 and Q2 about touch referral were significantly different between the two conditions C1 and I showing that the participants had perceived the mismatch between seen and felt touch in I.”

In the paper

“Regression analysis revealed that withdrawal movements were positively correlated with Q3 and Q7, validating the use of withdrawal movements to address ownership.”

In the paper

“And indeed, all participants in the conditions with the long virtual arm perceived an elongation of the dominant virtual limb and not a distortion of visual space in the depth axis.”

In the paper

“A regression of on , ownership and shows a positive slope for ownership (P = 0.0058) but no significant effects for the other two variables.”

In the paper

“However, a robust regression of on ownership and results in a highly significant positive slope for both variables (P<0.0005 in both cases).”

In the paper

“It is positively related both to Q3 (ownership) and Q7 (harmed).”

In the paper

“Additionally, proprioceptive drifts and the difference in the dispersion of movement data were significant in C2 and C3 but not in C4.”

In the paper

“Dropping the two non-significant terms results in a significant positive slope for ownership (P<0.01), but does not resolve the problem of the non-normality of the residual errors.”

In the paper

“Questionnaire scores for ownership were high in condition C2 and C3 and less in C4.”

In the paper

“However, at virtual arm length equal to the real one the fitted value of ownership is 4 and at quadruple the size the value is 3.3.”

In the paper

“These sensations were reported in questionnaire results and observed through participants’ motor defensive reactions in response to a threat towards the virtual hand.”

In the paper

“The case of harmed is more straightforward – there is a positive linear regression slope of on harmed (P<0.0001) with the residual errors satisfying normality (Shapiro Wilks P = 0.272)”

In the paper

“The same was also true for withdrawal movements and elongation.”

In the paper

“Here, during the elongation phase, each image of the virtual arm was different from the previous one inducing the sensations of having an arm that continuously extended but still moved synchronously with the real one and received congruent and synchronous tactile feedback in relation to a box that would not be reachable in reality.”

In the paper

“Furthermore, it has been proposed that the artificial body part should obey various morphological, anatomical and postural constraints (for a review see [6]) including the necessity for human body part resemblance.”

What the sources say

• Not checked yetcites [6] M Tsakiris, 2010, My body in the brain: a neurocognitive model of body-ownership., Neuropsychologia source

In the paper

“Moreover, a recent study showed that it is possible to induce the illusion of having a very small or giant body using synchronous visuo-tacile stimulation on the visible dummy body seen from first person perspective and the unseen real body [20].”

What the sources say

• Not checked yetcites [20] B van der Hoort, 2011, Being Barbie: the size of one’s own body determines the perceived size of the world., PLoS One source

In the paper

“Under this illusory perception, participants when asked to localize their real hand they are more likely to point closer to the rubber hand after the stimulation compared to before [7], [9].”

What the sources say

• Not checked yetcites [7] M Botvinick, 1998, Rubber hands ‘feel’ touch that eyes see., Nature source
• Not checked yetcites [9] M Tsakiris, 2005, The rubber hand illusion revisited: visuotactile integration and self-attribution., J Exp Psychol Hum Percept Perform source

In the paper

“In [8] the RHI was induced using a fake hand 91 cm beyond the real one, although with a lesser intensity compared to when using a normal sized fake arm.”

What the sources say

• Not checked yetcites [8] KC Armel, 2003, Projecting sensations to external objects: evidence from skin conductance response., Proceedings of the Royal Society of London Series B-Biological Sciences source

In the paper

“The difference between the participants’ estimations before and after the stimulation is called ‘proprioceptive drift’ and it is widely considered as a behavioral correlate of the ownership illusion, although a recent study [10] challenged the idea that there is a common underlying mechanism that connects drift with the subjective illusion of ownership.”

What the sources say

• Not checked yetcites [10] M Rohde, 2011, The Rubber Hand Illusion: Feeling of Ownership and Proprioceptive Drift Do Not Go Hand in Hand., PLoS ONE source

In the paper

“However, the extent to which gross asymmetries in the fake body can be assimilated remains unknown.”

What the sources say

• Not checked yetcites [8] KC Armel, 2003, Projecting sensations to external objects: evidence from skin conductance response., Proceedings of the Royal Society of London Series B-Biological Sciences source
• Not checked yetcites [22] F Pavani, 2007, The role of hand size in the fake-hand illusion paradigm., Perception source
• Not checked yetcites [23] M Schaefer, 2007, Morphing the body: illusory feeling of an elongated arm affects somatosensory homunculus., Neuroimage source

In the paper

“Additionally it has been shown that it is possible to generate an illusion of ownership of a rubber hand that was 3 cm larger than the real hand [22].”

What the sources say

• Not checked yetcites [22] F Pavani, 2007, The role of hand size in the fake-hand illusion paradigm., Perception source

In the paper

“Similar methods were used to give normal sized men the illusion of ownership over a very fat virtual body, again seen from a first person perspective and with synchronous visuo-tactile and visuo-motor stimulation [21].”

What the sources say

• Not checked yetcites [21] JM Normand, 2011, Multisensory stimulation can induce an illusion of larger belly size in immersive virtual reality., PLoS One source

In the paper

“It has been proposed that body ownership results from combining two types of knowledge: prior information that is innate or gained from the life experience (e.g. the appearance of our own body), and current multisensory information [6].”

What the sources say

• Not checked yetcites [6] M Tsakiris, 2010, My body in the brain: a neurocognitive model of body-ownership., Neuropsychologia source

In the paper

“Generally the induction of ownership illusions requires multisensory stimulation with the same spatiotemporal pattern on the real and fake body part [7], [14].”

What the sources say

• Not checked yetcites [7] M Botvinick, 1998, Rubber hands ‘feel’ touch that eyes see., Nature source
• Not checked yetcites [14] M Costantini, 2007, The rubber hand illusion: Sensitivity and reference frame for body ownership., Consciousness and Cognition source

In the paper

“However, the illusion of having a very long nose can be produced without such kinesthetic illusions. This occurs when a finger of a blindfold subject (S0) is manipulated by the experimenter to tap the nose of another subject (S1) who is sitting in front facing away from S0 while the experimenter simultaneously taps the nose of S0 [19].”

What the sources say

• Not checked yetcites [19] VS Ramachandran, 1998, The perception of phantom limbs. The D. O. Hebb lecture., Brain 121 (Pt source

In the paper

“Also simultaneous vibration on the biceps and triceps muscle tendons can induce the perception of a shrunken arm [18].”

What the sources say

• Not checked yetcites [18] MR Longo, 2009, Contraction of body representation induced by proprioceptive conflict., Current Biology source

In the paper

“It is clear that the probability is high for ownership to be scored at the highest level for equal length, but still at triple length the probability remains high, and only shows a decline at quadruple length.”

In the paper

“Furthermore, it has been found that just seeing an artificial limb 20 cm longer and connected to the body could result in topographic reorganization of the primary somatosensory cortex [23].”

What the sources say

• Not checked yetcites [23] M Schaefer, 2007, Morphing the body: illusory feeling of an elongated arm affects somatosensory homunculus., Neuroimage source

In the paper

“These findings revealed that the body representation is flexible and that it is possible to feel ownership towards a transformed and very asymmetric body that contradicts all the notions one has about the human body.”

In the paper

“Secondly, neurophysiological studies on monkeys (for a review, see [34]) and behavioral studies in humans e.g. [35] have shown that the brain encodes personal space (i.e. the space occupied by our body) differently from the peripersonal space”

What the sources say

• Not checked yetcites [34] M Graziano, 2002, How the brain represents the body: insights from neurophysiology and psychology; Hommel WPaB, editor: Oxford: Oxford University Press).
• Not checked yetcites [35] PW Halligan, 2003, Spatial cognition: evidence from visual neglect., Trends in Cognitive Sciences source

In the paper

“For example, in the study of [8] the intensity of the RHI was smaller when a distant fake arm was used (+91 cm) compared to a normal size fake arm as indicated by the questionnaire responses but not from skin conductance responses.”

What the sources say

• Not checked yetcites [8] KC Armel, 2003, Projecting sensations to external objects: evidence from skin conductance response., Proceedings of the Royal Society of London Series B-Biological Sciences source

In the paper

“and is thought to serve as a safety zone for the body, adapted to the body shape [41].”

What the sources say

• Not checked yetcites [41] MS Graziano, 2006, Parieto-frontal interactions, personal space, and defensive behavior., Neuropsychologia source

In the paper

“Proprioceptive drifts were found to be affected by elongation but only through the sensation that the real arm feels longer and not through ownership.”

In the paper

“These findings imply that the visual space was re-encoded in the virtual hand reference frames with a recalibration of the body segmental and postural configuration and a consequent update of the personal and peripersonal space under the perception of having a very long arm.”

In the paper

“Rapid changes in the primary somatosensory cortex (SI) due to visual exposure to a long artificial arm were found in the study of [23]”

What the sources say

• Not checked yetcites [23] M Schaefer, 2007, Morphing the body: illusory feeling of an elongated arm affects somatosensory homunculus., Neuroimage source

In the paper

“More interestingly, this modulation was significantly and positively correlated with the magnitude of the subjects’ sensations of having a long arm.”

What the sources say

• Not checked yetcites [23] M Schaefer, 2007, Morphing the body: illusory feeling of an elongated arm affects somatosensory homunculus., Neuroimage source