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 ordinary
familiarity of our own bodies can make it appear as though 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, one of the most common depictions 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 then
applied to the real hand and rubber hand, thus creating the subjective sense that
the rubber hand belongs to them demonstrated through altered proprioception and
neural activity in the premotor cortex (Botnicik and Cohen, 1998). This percept
is seen to be the result of visual-tactile correlation; usually a viewed and
felt touch occurring simultaneously must be occurring at one bodily location so
proprioception is pulled towards this (Graziano, 1999); when visual and
proprioceptive cues are in conflict, the more reliable visual cues are often considered.
This is theorised to be the result of bottom-up processing with the only
limitation being the need for synchronous brush strokes (Armel and
Ramachandran, 2003); the percept is created without any cognitive input, thus
suggesting that the illusion could potentially incorporate any object or
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 repeated
synchronous stimulations (Ramachandran et al, 1998), suggesting that body
representations are malleable enough to incorporate such objects into this
schema. Such misperception is said to be cognitively impenetrable; participants
fell for this 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 that using a far more realistic rubber hand; there
are reported limitations so what we will accept as a part our body (Pavani et al,
2000). This effect doesn’t consistently hold when pushing the limits of a
pre-existing bodily schema, suggesting some fixed body representation despite
visual-tactile coherence due to top-down constraints (Lloyd, 2007). According
to a number of studies, even a rubber hand is only embodied through
proprioceptive drift 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).
Knowledge of the form of our hand is essential for accurate movement in space
(Gandevia and Phegan, 1999), therefore the RHI only tends to occur alongside
synchronous brushstrokes, when correctly aligned with the subject’s real hand,
and when the form is largely accurate. 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 stability of representation.

Fixed representations may be
largely available in adulthood, however the RHI has displayed developmental
progression, perhaps indicating a certain degree of malleability early on in
life; body representations may become more fixed over time as we develop a
consistent view of our 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 which must be incorporated into current schema.
When conducting the RHI with children aged 4 – 9 years, Cowie, Tamar, and
Bremner (2013) found that felt position was captured more for the fake 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 children. 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 as you reach adulthood (Ehrsson et al,
2012). Children are far more reliant on sight as appose to proprioception early
in life for localisation of limbs (Graziano, 1999), allowing manipulation of
felt hand position to be far easier in children, with previous studies showing
that 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 late
childhood and adolescence (Bremner et al, 2013); at which point, the hand
typically reaches adult size, so the outcome of the RHI might be expected to
become less plastic and more stable (Bee, 2000). Pointing responses appear to
reach adult levels at 10 – 11 years old, at which point 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, demonstrating aspects
of fluidity throughout development. 

Malleability of
body representations in adult healthy cognition has been shown to be relatively
limited, depending upon 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 long been shown to demonstrate 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 that it was moved across (Weber, 1978). The size of stimuli moving across
sensitive regions like the palm were viewed as larger than the same size
stimuli moving across the back of the hand. Further studies have suggested that
stimuli moved across the width of the hand are perceived as 40% larger than
those running across the length (Longo and Haggard, 2011). This results from
somatosensory maps which show highly disproportionate representation of skin
regions depending upon their sensitivity, also known as cortical magnification;
knowledge of our bodies is neutrally mediated and reflected through innate
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 use to perform otherwise
impossible dexterous behaviours. This has also been found to a larger degree
when estimating body size through the Body Image Task (BIT), during which
participants had to judge the location of their limbs when given an image of
their head as a landmark; healthy adults overestimated their
shoulder-width-to-height ratio by over 40% (Fuentes, Longo, and Haggard, 2013).
Such distortions have also been shown through position sense; even with the
absence of vision, adults are relatively poor in localisation of body parts,
seen to also be a result of these somatosensory maps. When participants were
asked to judge the locations of parts of their arm, this localisation was inaccurate,
and these parts were perceived as closer together than the actual locations;
suggesting a distorted representation of arm length (Gurfinkel and Levick,
1991). Similar results have been found when judging location on the back of the
hand; hand width is often 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 magnitude of these
distortions is reduced significantly when judgements are made about the palm of
the hand. 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.

Body
representations can also appear to be fluid in healthy cognition depending upon
several external inputs which may manipulate how we view our body. In a study
by Gandevia and Phegan (1999), administration of anaesthesia to the thumb
significantly increased its perceived size; perceived size increased 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, thus causing the
brain to accept these adjacent locations as associated with the thumb. This
highlights the lability of body representations in healthy cognition, with
anaesthesia even impacting our cortical representations in the somatosensory
cortex, suggesting that are mode of processing these inputs may not be as
stable as proposed. Similar findings demonstrate the role of pain in
manipulations of body representations; when a cold-sensitive class of C fibres,
producing a sensation of pain, were increased in input 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 our social experiences, through
which distortions of body representations have been shown across much larger
fields, often encapsulating the whole body. According to Mead (1934), larger
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 it is suggested that they exacerbate manipulation of body
image on a large scale, even in healthy cognition.

Body
representations have largely been studied in a clinical population due to the
extreme malleability they present; despite pathologies not reflecting normal
functioning, they still demonstrate how body representations can be
manipulated. Key pathologies which appear to reflect vast discrepancies in
judgement of body size are Eating Disorders, specifically Anorexia Nervosa;
classified as disturbance in the way one’s body weight or shape is experiences
(DSM-IV, 1994), often estimating body size as larger than objectively true.
Body image dysfunction is integral to this syndrome, indicating some degree of
inability to accurately assess your own body size, often attributed to
unrealistic social standards (Bruch, 1962); with social input important in
assessing body representation, as discussed previously. Despite, several
studies suggesting a poor ability in gauging your body size to be key in
Anorexia, there is debate over the specific nature of disturbances and whether
the main deficit within this disorder is this perceptual body size distortion,
or whether it is more reliant upon cognitive evaluative dissatisfaction, based
largely upon attitudinal body image (Cash and Deagle, 1997). Previous studies
have equated these variables and mostly assess perceptual distortion due to
this being deemed as a more accessible measure (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). Research comparing perceptual and attitudinal
measures of Anorexia in women demonstrated that metric estimations of body
size, through measures requiring estimations of body size as particular sites
(e.g. Askevold, 1975), were significantly poorer than in a control group with
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 the extent of discrepancy between
self and ideal percept (e.g. Cash and Szymanski, 1995), demonstrated
substantially larger effect sizes (1.10 – 1.13), suggesting a greater reliance
on social input forming exceptionally poor body attitudes in Anorexia, as
appose to inaccuracy in body representations. Although, another extreme
disorder which reflects large perceptual disturbances is Schizophrenia, with
many patients demonstrating lack of bodily awareness and the knowledge that, in
adulthood, these representations are largely fixed (Ehrsson et al, 2004). Previous
findings have shown that the RHI is intensified and has a rapid onset in
Schizophrenia; demonstrating consistency with the notion of a weaker and more
flexible sense of self (Peled et al, 2003). Following this, the RHI was
conducted on a group of Schizophrenia patients using skin-conductance
responses, proprioceptive drift, and temperature measurements to determine the
strength in these patients compared to normally functioning individuals
(Thakkar et al, 2011). The RHI was consistently stronger in patients, with more
vivid self-reported feelings of ownership, and with proprioceptive drift being
three times in the synchronous condition larger than the healthy controls.
Increased vividness was also associated with schizotypty symptoms in healthy
participants; suggesting that malleability in body representations has an
association with psychosis. Skin cooling in the stimulated hand was also
present following this illusion, relating to a sense of disownership 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 regarding stability of body
representations is Autism Spectrum Disorder (ASD), despite the idea that these
individuals demonstrate poor empathy and imitation, both of which have been
linked to malleability of body 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 this illusion, with a more fixed
representation than normally-functioning adults, whilst TD children have previously
been shown to be much more malleable in this respect (Haswell et al, 2009). It
was theorised that children with ASD depend more heavily on proprioceptive than
visual input when the two are incongruent, largely dissimilar to TD children
who are far more efficient 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 and empathy
(Lombardo et al, 2009). Falling for the RHI and this slight fluidity in body
representation has been related to the ability to empathise with others, this
being 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,
research suggests that some level of plasticity in body representations is
normal, even in healthy cognition; with extreme stability sometimes indicating
disordered cognition, suggesting that body representations aren’t completely
fixed. This flexibility can be exacerbated alongside familiar external factors;
like experiencing pain and social comparison, and is especially pronounced throughout
early to mid-childhood. Large distortions in body representations are a
significant aspect of certain psychopathologies, especially Schizophrenia,
however Anorexia which is also said to be a disorder of body representation, is
based on attitudinal dysfunction as appose to perceptual deficits. Despite clear
demonstrations of lability, it needs to be understood that 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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