The use of realistic and mechanical hands in the rubber hand illusion, and the relationship to hemispheric differences
Introduction
The rubber hand illusion (RHI) plays a key role in the study of how the inner representation of one’s body changes over time based on experience. In the standard procedure, one’s hand is hidden, and a fake hand is visible. When both hands are stimulated at the same time, for instance by a paintbrush, the visual experience of seeing the fake hand touched is combined with the corresponding tactual sensation. After less than a minute, most participants experience a sense of ownership of the fake hand, including a sense that the fake hand feels the touch (Botvinick & Cohen, 1998, for a review see Serino & Haggard, 2010). The illusion is strongest following synchronous stroking, weaker with asynchronous stroking, and weaker with only visual exposure to the fake hand and no stimulation (e.g. Longo et al., 2008, Rohde et al., 2011).
The conditions necessary for the illusion have been debated in the literature. Some authors have suggested that the correlation between vision and touch is sufficient for inducing the experience of ownership of objects totally different from a hand, for instance a table (Armel & Ramachandran, 2003). Other authors, however, have concluded that the fake hand has to have a plausible appearance, and be placed in a plausible relationship to the body. We review this literature below, and next we consider reasons to predict a difference in the strength of the illusion when the left hand or the right hand is stimulated (Ocklenburg, Rüther, Peterburs, Pinnow, & Güntürkün, 2011), and how this might relate to the appearance of the fake hand. Our study addresses both the role of appearance, by using two types of hands, and the role of laterality, by testing both left and right hands of each participant.
Section snippets
The appearance of the fake hand
In our study, we revisited the role of the appearance of the hand. In particular, we compared hands that looked like human hands, and hands that had the size and shape of a hand, including the presence of fingers, but were clearly non-biological. There is empirical evidence that the plausibility of the hand determines the strength of the illusion. Tsakiris and Haggard (2005) compared fake hands with wooden sticks, and the latter failed to elicit the illusion. A rectangular wooden block has been
Hemispheric differences and body representation
The right hemisphere has been connected to a stronger awareness of the physical and mental self, with evidence coming from neurological patients and neurophysiological techniques (Feinberg and Keenan, 2005, Karnath and Baier, 2010, Keenan et al., 2001). Recently, differences in representations related to self have been addressed through the RHI. There is evidence that the right hemisphere accepts a fake hand more easily than the left hemisphere. Skin conductance response to the fake hand being
Different measures of the strength of the illusion
Two measures of the illusion were taken. The objective measure required participants to close their eyes, and point toward the middle finger of the illuded hand with the index finger of the non-illuded hand. Proprioceptive drift toward the fake hand, and away from the real hand, measures the degree of change in the representation of the position of the real hand. The subjective measure included three questions selected and adapted from Botvinick and Cohen (1998). Drift and subjective experience
Experiment
As mentioned in the introduction we conducted an experiment that compared two types of hands. One type was realistic and was created from casting a real pair of male hands. The other hand matched the realistic hand in size but was made of metallic wires (see Fig. 1). We manipulated appearance and tested both left and right hands for each participant in a large sample (N = 120) of young adults. A subset of the same data, excluding the mechanical hand and combined with measures of
Cross-manual pointing
The distance between the position of the middle finger of the real hand and the pointed location is plotted in Fig. 2. The larger the error the greater the drift toward the fake hand.
Drift was normally distributed; thus parametric analyses were run. Two repeated factors, Hand (left, right) and Brushing (visual, asynchronous, synchronous), were placed in an ANOVA with Appearance as a between-subject factors. The dependent variable was the proprioceptive error in pointing to the real hand.
Discussion
We explored the role of the appearance of the fake hand on the strength of the RHI, and whether effects of appearance were lateralized. We contrasted hands that shared many of the characteristics of real hands; however, one was mechanical, and therefore less plausible in contrast to a more realistic one. We tested both a left and right version of each hand. We expected that the mechanical hand would lead to a reduced strength in the illusion, and that this reduction would be greater when the
Acknowledgment
We would like to thank Carole Bode for designing and building the fake and mechanical hands used in the study.
References (47)
- et al.
The rubber hand illusion in a mirror
Consciousness and Cognition
(2011) - et al.
Haptic perception after a change in hand size
Neuropsychologia
(2010) - et al.
The rubber hand illusion: Sensitivity and reference frame for body ownership
Consciousness and Cognition
(2007) - et al.
Evidence for a new conceptualization of semantic representation in the left and right cerebral hemispheres
Cortex
(2004) - et al.
Where in the brain is the self ?
Consciousness and Cognition
(2005) - et al.
Manipulating noise frequencies alters hemispheric contribution to decision making
Brain and Cognition
(2007) - et al.
The effect of similarities in skin texture and hand shape on perceived ownership of a fake limb
Body Image
(2008) - et al.
Hemispheric asymmetries in cerebral cortical networks
Trends in Neurosciences
(2003) - et al.
On the hemispheric specialization for categorical and coordinate spatial relations: A review of the current evidence
Neuropsychologica
(2003) - et al.
Pseudoneglect: A review and meta-analysis of performance factors in line bisection tasks
Neuropsychologia
(2000)
Spatial limits on referred touch to an alien limb may reflect boundaries of visuo-tactile peripersonal space surrounding the hand
Brain and Cognition
Visual enhancement of touch and the bodily self
Consciousness and Cognition
On the other hand am I rational? Hemispheric activation and the framing effect
Brain and Cognition
The rubber hand illusion modulates pseudoneglect
Neuroscience Letters
The rubber hand illusion in complex regional pain syndrome: Preserved ability to integrate a rubber hand indicates intact multisensory integration
Pain
Touch and the body
Neuroscience and Biobehavioral Reviews
The role of the right temporoparietal junction in maintaining a coherent sense of one’s body
Neuropsychologia
Having a body versus moving your body: Neural signatures of agency and body-ownership
Neuropsychologia
Brain connectivity and the self: The case of cerebral disconnection
Consciousness and Cognition
Projecting sensations to external objects: Evidence from skin conductance response
Proceedings of the Royal Society of London. B: Biological Sciences
Mislocalizations of touch to a fake hand
Cognitive, Affective, & Behavioral Neuroscience
Rubber hands ‘feel’ touch that eyes see
Nature
Tool-use induces morphological updating of the body schema
Current Biology
Cited by (20)
The rubber hand universe: On the impact of methodological differences in the rubber hand illusion
2019, Neuroscience and Biobehavioral ReviewsCitation Excerpt :In addition, bodily self-awareness has been predominantly associated with the right cortical hemisphere (for a recent review see Blanke et al., 2015), and therefore, in right-handers, the non-dominant left hand might be more directly linked to processes affecting body ownership. Some studies did not find substantial differences between hands (Mussap and Salton, 2006; Niebauer et al., 2002; Smit et al., 2017; Zeller and Hullin, 2018) or only side effects such as a higher relationship between proprioceptive drift and subjective ratings for the left compared to the right hand (Bertamini and O’Sullivan, 2014). However, other studies reported higher subjective ratings (Ocklenburg et al., 2011; Reinersmann et al., 2013), larger proprioceptive drifts (Dempsey-Jones and Kritikos, 2019) and increased skin conductance responses after a threat (Ocklenburg et al., 2011) for the left compared to the right hand.
The role of visual similarity and memory in body model distortions
2016, Acta PsychologicaCitation Excerpt :If this is the case, an object with greater visual similarity to a real hand (e.g. a rubber hand) might depict distortions that are closer to the hand than the rake. This idea would be in line with research on embodiment showing that objects can be experienced as part of one's body (i.e. as embodied) when they share important structural and visual information about the body part (Bertamini & O'Sullivan, 2014; Holmes, Snijders, & Spence, 2006; Tsakiris, Carpenter, James, & Fotopoulou, 2010; Tsakiris & Haggard, 2005). Studies on the rubber hand illusion suggest that the degree to which fake body parts (rubber hand and non-biological mechanical hand) can be embodied depends on the similarity between the actual body part and the tested stimulus.
Hand cooling enhances the proprioceptive drift during rubber hand illusion
2022, Research SquareExperience-Dependent Modulation of Rubber Hand Illusion in Badminton Players
2022, Journal of Sport and Exercise Psychology