According any successful interactions. The regular familiarity of our

According to Pazzaglia and
Zantedeschi (2016), a human body representation is an internal portrayal of our
corporal structure and allows for feelings of ownership over our limbs, with
such knowledge being essential for any successful interactions. The regular
familiarity of our own bodies can make it appear that the body representations
we experience are largely infallible. Many normally functioning individuals
take this supposedly fixed experience of the body for granted, with distortions
and malleability often attributed to numerous neurological and psychiatric
conditions (Longo, 2017). Despite this, research has shown that some degree of
fluidity in body representations of normally functioning individuals may be an
aspect of healthy cognition. This essay shall explore the extent to which body
representations can be manipulated in humans with healthy cognition and those
with apparent disorders of bodily perception, with some suggesting that a small
amount of flexibility in normal cognition is vital for social interaction, and
others revealing that not all disorders which seemingly affect our bodily
perceptions involve distortions in body representations. Ultimately, it will
suggest that body representations have some degree of malleability across individuals,
however there are many external limitations and exacerbating factors that must
be accounted for when determining this fluidity.

An automatic feeling of ownership
over our limbs is a fundamental aspect of body representation (Ehrsson et al,
2004). Therefore, a common depiction of fluidity in body representations in
healthy cognition is the Rubber Hand Illusion (RHI); an illusion of limb
ownership during which the subject’s real hand is occluded and a rubber hand is
placed in front of them. Synchronous brush strokes are applied to the real hand
and rubber hand, creating the subjective sense that the rubber hand belongs to
them, demonstrated through altered proprioception and premotor activity (Botvinick
and Cohen, 1998). This percept is the result of visual-tactile correlation;
usually a viewed and felt touch occurring simultaneously must be occurring at
one bodily location (Graziano, 1999); when visual and proprioceptive cues are
in conflict, the more reliable visual cues are considered. This is theorised to
be the result of bottom-up processing with the only limitation being the need
for synchrony (Armel and Ramachandran, 2003); the percept is created without
cognitive input, thus suggesting the illusion could incorporate any instance,
demonstrating exceptional malleability of body representation in normally
functioning participants. Previous studies have shown that subjects were able
to perceive touch sensations arising from a table following synchronous
stimulations (Ramachandran et al, 1998), suggesting that body representations
are malleable enough to incorporate such objects. Misperception is cognitively
impenetrable; participants fell for the illusion even when they knew they were
viewing an experimenter’s hand rather than their own (Welch, 1972). However,
self-report measures of intensity of ownership demonstrate that using a table
for such an illusion elicits a reduced response than using a realistic rubber
hand; there are limitations to what we will accept as a part of our body
(Pavani et al, 2000). This effect doesn’t consistently hold when pushing the
limits of a pre-existing bodily schema, suggesting fixed body representation
despite visual-tactile coherence due to top-down constraints (Lloyd, 2007). Studies
suggest even a rubber hand is only embodied when of suitable form and
orientation (Haans et al, 2008; Tsakiris and Haggard, 2005); subjects were
sensitive to inconsistencies in orientation when turning the hand by just 10° (Constantini
and Haggard, 2007). This indicates that our body representations must be fluid
to some degree as we are able to incorporate external components into this
schema, however, there are limits to the RHI which demonstrate some implicit
knowledge and representation stability.

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Fixed representations may be
largely available in adulthood, however the RHI has displayed developmental
progression, perhaps indicating a degree of malleability during childhood; body
representations may become more fixed as we develop a consistent view of bodily
limits. Children aged 18 – 30 months are more likely to make scale errors when
integrating body-size information into actions (deLoache et al, 2004);
suggesting plasticity in representations due bodily changes throughout childhood.
When conducting the RHI with children aged 4 – 9 years, Cowie, Tamar, and
Bremner (2013) found that felt position was captured more for the rubber hand
in children than adults; children’s’ post-illusion pointing drifted
significantly further towards the fake hand, suggesting that vision of an
appropriately oriented hand is a powerful cue to own-hand position in childhood.
This indicates that children have access to multisensory bodily perception in
infancy, with sensitivity to visual-tactile cues causing them to respond to the
rubber hand as if it was their own. However, there may be a late-maturing
visual-proprioceptive process which underlies self-localisation and reduces
malleability of body representations in adulthood (Ehrsson et al, 2012). Children
are more reliant on sight than proprioception for localisation of limbs
(Graziano, 1999), allowing manipulation of felt hand position to be easier in
children; this effect can be up to three times larger in children compared to
adults (Cowie, Sterling, and Bremner, 2016). The optimal combination of multisensory
cues appears to show protracted development throughout infancy and into
adolescence (Bremner et al, 2013); at which point, the hand typically reaches
adult size, so the outcome of the RHI might be expected to develop stability
(Bee, 2000). Pointing responses appear to reach adult levels at 10 – 11 years
old when children perceive hand location using an adult-like balance of sensory
cues (Cowie, Sterling, and Bremner, 2016). This suggests that body representations
may be relatively fixed in adulthood, however plasticity is required in
childhood allowing for incorporation of new information into our body schemas.

Malleability of
body representations in healthy adult cognition is relatively limited, depending
on held knowledge of bodily capabilities, although it has been suggested that
large and systematic distortions of body representations may be a key aspect of
healthy cognition (Longo, 2017). Tactile size and distance perception of limbs
has demonstrated significant distortions; when moving a compass across various
areas of the body, the distance between the points is perceived to change
depending upon the region of skin (Weber, 1978). The size of stimuli moving
across sensitive regions, like the palm, were viewed as larger than the same
size stimuli across the back of the hand. Further studies have suggested that
stimuli moving across the hand width are perceived as 40% larger than those
across the length (Longo and Haggard, 2011). This results from inbuilt somatosensory
maps which show disproportionate representation of skin regions depending upon
sensitivity, also known as cortical magnification; bodily knowledge is mediated
and reflected through topographic maps in the brain, demonstrating this unique organisation
(Pazzaglia and Zantedeschi, 2016). This has been modelled through the Penfield
Homunculus (Penfield and Boldrey, 1937); we are adapted to have high tactile
sensitivity on specific skin surfaces, allowing us to perform otherwise
impossible dexterous behaviours. This has been found when estimating body size
through the Body Image Task (BIT), during which participants judged their limb-location
when given an image of their head as a landmark; healthy adults overestimated
shoulder-width-to-height ratio by over 40% (Fuentes, Longo, and Haggard, 2013).
Distortions have been shown through position sense; even with absence of vision,
adults are poor in localisation of body parts. When participants judged the
locations of parts of their arm, localisation was inaccurate; these parts were
perceived as closer together than in reality, suggesting a distorted
representation of arm length (Gurfinkel and Levick, 1991). Similarly, when
judging location on the back of the hand, hand width is overestimated, whilst finger
length is underestimated in a radial-gradient formation – increasing
progressively from the thumb to the little finger (Longo and Haggard, 2012);
however, the distortion magnitude reduced significantly when judgements were
made about the palm. To conclude, body representations may show some degree of
fluidity, even in healthy cognition, as shown by these distortions of
judgement; however, this also demonstrates that we have a fixed means of
processing these inputs through the somatosensory cortex, indicating relative
fixedness of body representations in adults.

Body
representations can also appear to be fluid in healthy cognition depending on
external inputs. In a study by Gandevia and Phegan (1999), administration of
anaesthesia to the thumb significantly increased perceived size by 60 – 70 %.
They proposed this to be the result of the acute removal of afferent input from
the thumb, resulting in the enlargement of the receptive fields of the cortical
cells representing skin areas surrounding this site. This causes the brain to accept
adjacent locations as associated with the thumb. Such results highlight the
lability of body representations in healthy cognition; anaesthesia impacts cortical
representations in the somatosensory cortex, suggesting that the mode
processing these inputs may not be as stable as proposed. Similar findings
demonstrate the role of pain in such body representation alterations. When input
of a cold-sensitive class of C fibres, producing a sensation of pain, was
increased in the thumb, this also caused the thumb to feel larger (Calford and
Tweedale, 1991). These fibres limit the receptive fields of the somatosensory
neurons at this site, producing feelings of enlargement. However, such findings
have been shown to be limited to smaller body parts like fingers and lips,
perhaps suggesting that our overall body size is relatively fixed despite
external inputs. Another significant external input that should be accounted
for is social experiences, through which distortions of body representations
often encapsulate the whole body. According to Mead (1934), large distortions
of viewed body size may reflect a generalisation based upon body schema created
through social interactions; we construct what we believe our own body should
look like based upon the observed bodies of others. Therefore, external inputs
must be assessed when determining fluidity of body representations, as they may
exacerbate manipulation of body image on a large scale, even in healthy
cognition.

Body
representation distortions have mostly been studied in a clinical population
due to the extreme malleability they appear to present. Key pathologies reflecting
vast discrepancies in body size judgements are Eating Disorders, specifically
Anorexia Nervosa; classified as disturbance in the experience of one’s body
weight or shape (DSM-IV, 1994), often subjectively overestimating body size.
Body image dysfunction is integral to this syndrome, indicating some degree of
inability to accurately assess own-body size. This is often attributed to
unrealistic social standards (Bruch, 1962); with social input important in
assessing body representation. However, there is debate over the specific
nature of body-image distortions in Anorexia, with some suggesting that the
main deficit is perceptual body-size distortion, and others implying greater
reliance on cognitive evaluative dissatisfaction, based on attitudinal body
image (Cash and Deagle, 1997). Previous studies have equated these variables
and assess Anorexia through the more accessible measures of perceptual
distortion (Hsu and Sobekiewicz, 1991), however others suggest that distortions
of body representation may not be as fundamental to Anorexia as previously
thought (Cash and Brown, 1987), and that body-image disturbances should be
abandoned as a diagnostic criterion for Eating Disorders (Hsu, 1982). A
meta-analysis by Cash and Deagle (1997), found that perceptual estimations of own-body
size by women with Anorexia, measured through metric estimations of own-body
size (e.g. Askevold, 1975), were significantly poorer than in controls, but
with only moderate effects of 0.61 – 0.64. However, attitudinal measures such
as, adjustment of an image to convey body size preferences, combined with
judgements of actual body size to quantify discrepancy between self and ideal
(e.g. Cash and Szymanski, 1995), demonstrated substantially larger effect sizes
in Anorexia than controls (1.10 – 1.13), suggesting a greater reliance on
social input forming poor own-body attitudes in Anorexia, as appose to
inaccuracy in body representations. Although, another extreme disorder reflecting
large perceptual disturbances is Schizophrenia, with patients demonstrating
lack of bodily awareness and the knowledge that, in adulthood, these
representations are fixed (Ehrsson et al, 2004). Previous findings have shown
that the RHI is intensified with rapid onset in Schizophrenia; demonstrating
consistency with the notion of a weaker and more flexible self (Peled et al,
2003). The RHI was conducted on a group of Schizophrenia patients using
skin-conductance response, proprioceptive drift, and temperature measurements
to determine the strength in patients compared to normally-functioning
individuals (Thakkar et al, 2011). The RHI was consistently stronger in patients,
with more vivid feelings of ownership, and with proprioceptive drift in the
synchronous condition being three times larger than controls. Increased
vividness was also associated with schizotypy symptoms in healthy participants;
suggesting that extreme malleability in body representations is associated with
psychosis. Skin cooling in the stimulated hand was also present following this
illusion, relating to dis-ownership of the stimulated hand (Moseley et al,
2008). Schizophrenia demonstrates extreme malleability in body representations,
largely associated with psychotic symptoms, with some patients experiencing the
illusion even before tactile stimulation began. To conclude, disorders
appearing to impact body representation may not always involve perceptual
discrepancies, however certain pathologies demonstrate huge flexibility in
these representations, suggesting that they aren’t fixed across the population.

Another
pathology, which has been relatively ignored in discussions of body
representation, is Autism Spectrum Disorder (ASD), despite the idea that individuals
with ASD demonstrate poor empathy and imitation abilities, both of which have
been linked to malleability of representations (Cascio et al, 2012).  When carrying out the RHI among children with
ASD, in comparison to typically developing (TD) children, it was shown that
those with ASD took longer to fall for the illusion, with a more fixed
representation than normally-functioning adults; whilst TD children have
previously been shown to be more malleable (Haswell et al, 2009). It was
theorised that children with ASD depend more heavily on proprioceptive than
visual input when the two are incongruent; unlike TD children who show
efficiency at combing visual-tactile cues. This perhaps demonstrates
malleability of body representation being compromised in those with ASD,
analogous with a modified cortical representation of the bodily self; giving
rise to a diminished capability for perspective-taking (Lombardo et al, 2009).
Falling for the RHI has been related to the ability to empathise with others; a
complex social process requiring the integration of multiple affective
components (Decety, 2010). This suggests that, perhaps some small degree of
fluidity in body representations is important in normally-functioning
individuals, and completely fixed body representations are indicative of social
disorders such as ASD.

Overall, some level
of plasticity in body representations may be normal, even in healthy cognition,
with extreme stability sometimes indicating disordered cognition; thus,
suggesting that body representations aren’t completely fixed. This flexibility
can be exacerbated alongside external factors; like experiencing pain and
social comparison and is pronounced throughout early to mid-childhood. Large
distortions in body representation are a significant aspect of certain
psychopathologies, especially Schizophrenia. However, Anorexia, also said to be
a disorder of body representation, is based on attitudinal dysfunction as
appose to perceptual deficits. Despite clear demonstrations of lability, there
are limitations to this, especially in healthy cognition, which restrict any
extreme malleability. These involve held knowledge of bodily capabilities and
the fixed areas of the brain in which sensory inputs are processed; the
somatosensory cortex, despite demonstrating distortions of body representation,
is a relatively fixed means of processing these inputs and provides limitations
to flexibility.

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