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1Summary Cognitive Neuropsychiatry
Eating disorders
Engel, M.M. & Keizer, A. (2018). Body representation disturbances in visual perception and
affordance perception persist in eating disorder patients after completing treatment.
Body image disturbances are a key feature of eating disorders and often keep existing in patients who
completed their eating disorder treatment. The current study is the first study investigating mental
body representations instead of just looking at cognition and affect (often measured by interviews and
questionnaires). They compare eating disorder patients (ED), patients who completed their treatment
(CEDT) and healthy controls (HC).
Introduction
An eating disorder is a severe mental illness that causes impairments in psychosocial functioning
and/or physical health. There is an incorrect notion of one’s own body size or shape, which is called a
body image disturbance (BID). BID is strongly associated with the development and maintenance of
an eating disorder. Relapse is predicted by the severity of BID. To ensure fewer relapses and
optimize treatment, a clearer understanding of BID is important in patients that completed their eating
disorder treatment. The study focuses on a cognitive neuroscience perspective: the brain processes
primarily multimodal information pertaining to the body from different sensory modalities and
integrates it into a coherent and abstract higher order representation of the body. BID is often seen as
a mental body image, emphasizing the visual aspects of the mental body representation, however BID
also includes tactile, cognitions and affect. Studies of BID in ED patients have found disturbances in
the bodily attitudes, visual perception of the body, haptic perception, tactile perception and affordance
perception/bodily action. However, existing interventions are mostly aimed at improving just cognition
and visual perception (by CBT and mirror exposure). There is no standardized intervention model for
BID, which causes a lot of heterogeneity. Recovery is often determined by BMI, self-report and
questionnaires. However, BID cannot be assessed fully by using only these measures. BID persists
after recovery, causing BID to be seen as a trait factor (a stable pattern of behavior, thoughts and
emotions over a long period of time). In the current study, BID is assessed in four domains (bodily
attitudes, visual perception of body size, tactile perception and affordance perception) in ED patients,
CEDT patients and healthy controls. It is measured by a Visual Size estimation task, a Tactile
estimation task and the Hoop task. They hypothesize that there are no differences between these
tasks in CEDT and ED patients. They do expect more negative attitudes in ED patients compared to
CEDT patients and healthy controls.
Methods and results
ED and CEDT patients were recruited from different institutions in the Netherlands. All ED patients
were provided with treatment according to the national guidelines for care for ED in the Netherlands,
which mainly concerns CBT. Demographics were asked by using a questionnaire. The BMI in healthy
controls was significantly higher than in ED and CEDT patients. They checked for correlations
between BID measures and handedness, education and past pregnancy. No significant relations were
found and these measures were not used as covariates.
Body attitude test: this is a questionnaire for patients with AN and BN and is a valid and reliable
instrument to measure the subjective attitude of the body.
—> results: ED patients had a significantly higher total BAT score compared to CEDT patients and
HC. No differences were found between CEDT and HC,only on the scale ‘lack of familiarity with one’s
own body’. ED patients thus held stronger negative attitudes towards their body.
Visual size estimation: this is used to measure visual body perception. Participants have to estimate
their width of the shoulders, waist and hips by placing stickers on a wall. After their estimation, the
, 2
actual size was measured by the experimenter. The percentage of misestimation was calculated
(estimated - actual / estimated * 100).
—> results: both ED and CEDT had a higher percentage of misestimation of shoulder, waist and hip
width compared to HC. ED patients had a higher percentage of misestimation on waist and hips width
compared to CEDT, but not on shoulder width (this was approximately the same).
Tactile estimation task: in this task perception of tactile distances of the arm and the abdomen
(emotionally salient body part) was measured. The estimation of the width of the stimuli was made
with the index finger and thumb by placing them on a tablet.
—> results: there is a main effect of distance and body part, but there was no significant main effect
for group. there are no differences in tactile estimation on arm and abdomen between all groups.
Hoop task: participants were asked to judge whether their body would fit through a hoop (range 24-52
cm). If the hoop was judged by the participant to be big enough, the participant had to step inside the
hoop and lift it over her head. Afterwards, the participant was instructed to step through the hoops
until the smallest one was found. The percentage of misestimation was calculated.
—> results: ED and CEDT patients had a larger percentage of overestimation compared to HC. ED
patients had the largest overestimation percentage.
Discussion
Results of this study confirm the expectation on the existence of BID in CEDT patients in the visual
perception (visual size estimation) and affordance perception (hoop task) domain, whilst being absent
in the bodily attitudes. ED patients still show the largest overestimations but CEDT patients are
intermediate between HC and ED. In contrast to expectation, no differences in tactile perception were
found between ED, CEDT and HC.
Limitations of the study are the use of self-report measures. In previous work weight was always
measured, however no correlations were ever found between weight and the measures of body
image, so it seems that perceived body size and weight are independent from each other. In addition,
no overestimation of tactile distances in ED were found, which is not in accordance with previously
reported findings. Fewer tactile trials were used in this study, which could account for the absence of
significant results.
The absence of strong negative bodily attitudes in CEDT patients could substantiate the theory on the
effect of the current therapy focus, where patients learn to recognise dysfunctional thoughts and new
strategies are taught to cope with these cognitions and negative affect, while too little attention is
spent on other BID symptoms such as disturbances in visual body perception and affordance
perception. The significance of sensory domains in relation to body image should be recognized and
integrated in standardized ED treatments. Studies such as the Rubber Hand Illusion show that it is
possible to change the internal body representation when sensory modalities are targeted (afterwards
patients estimate their hand size more accurately). Also in virtual reality effects can be found. It is thus
evident that body representation can be altered. Research to more effective treatments addressing
multiple (sensory) modalities in ED is advised.
Keizer, A., Van Elburg, A., Helms, R., Dijkerman, C. (2016). A virtual reality full body illusion improves
body image disturbance in anorexia nervosa.
Introduction
The disturbed experience of body size in AN is central to the disorder and has been linked to
development, prognosis and maintenance of AN, as well as relapse. Treatment often focusses on
, 3
changing bodily cognitions and visual perception of the body instead of targeting the full multisensory
spectrum of the disturbance.
The representation of our body can be divided into separate sub-representations, for example body
image (perceptual body representation) and body schema (used for motor action). There are also
other sub-representations. All these models propose that the way in which we experience our body
depends on input from multiple sensory modalities. It has for example been found that body image
disturbances in AN also manifest themselves in overestimation of tactile stimuli, disturbed haptic
perception, altered integration of visual and proprioceptive information etc. AN patients have a
diminished Size Weight Illusion, implying distorted haptic-visual-proprioceptive integration. AN
patients disintegrate physical from subjective dimensions of bodily experiences. The underlying
processes causing this are still unclear.
Both acute and recovered AN patients are more susceptible to experiencing the Rubber Hand Illusion
(RHI). In the RHI, an actual body part and a fake body part are simultaneously touched, which causes
a visuo-tactile conflict in the brain. The brain integrates the two separate streams (seeing the rubber
hand, feeling touch on its own hand) into one single event. After inducing the RHI, AN patients did not
overestimate their hand size anymore. So, it is possible to change the disturbed experience of body
size in an experimental setting using a multisensory illusion. A possible explanation of the
effectiveness of the RHI, both in synchronous and asynchronous conditions, is that participants based
their hand size estimates on the most recent available visual input. It is now important to investigate
whether improvements in body size estimation also occur for body parts that are more emotionally
salient, such as the abdomen or the hips. Therefore, in the current study they induced a full body
illusion (FBI) with VR. Before the FBI, AN patients estimated the width and circumference of several
parts of the body. From a clinical experience we know that AN patients often struggle with a
discrepancy between knowing their size and feeling their size, so there is a difference between
cognition and experience. In this study, it is important that participants report how they feel about their
body instead of using their knowledge about body size stored in memory. The experienced (feeling)
part can be affected by the FBI.
In the current study, the hypothesis is that after the FBI, there is a decrease in overestimation in AN
patients. They expect that changes in size estimations after FBI would occur most strongly for the
body parts that are less emotionally salient, as AN patients show distortions in size estimations
especially for body parts that are highly emotionally salient. This has been found to be related to
negative attitudes about those body parts, which may in a top-down fashion affect size estimates.
Methods
30 AN patients and 29 healthy controls participated in the study. They filled out several questionnaires
(Body Attitude Test & Eating Disorder Inventory) and they had to estimate the width and
circumference of several parts of their body. The FBI was induced twice, once with synchronous
visuo-tactile stimulation and once with asynchronous viso-tactile stimulation. After the VR trial,
participants again estimated the size of their body and they filled in the Embodiment Questionnaire,
assessing how they subjectively experienced the illusion. Then the experimenter measured
participants’ actual body dimensions and weight. About 2 hours and 45 minutes later, a follow-up
measure took place where participants again estimated their body size.
Results
- AN patients and HC had an equally strong experience of the FBI, and as assumed both groups
experienced more ownership and agency over the virtual body and a stronger shift in location towards
the virtual body in the synchronous compared to the asynchronous (control) condition.
- AN patients show larger percentages of misestimation of shoulder, abdomen and hip width.
- There was a significant decrease in size estimation in shoulder and hip width in the pre to post
synchronous condition. In shoulder width, there was also a decrease in the asynchronous condition.
, 4
- AN patients show larger percentages of misestimation of shoulder, abdomen and hip circumference.
- There was a significant decrease in estimation in shoulder, abdomen and hip circumference in both
synchronous and asynchronous conditions.
→ AN patients showed a larger decrease in percentage of misestimation from pre to post
synchronous as well as a marginally significant decrease from pre to post asynchronous
illusion in the abdomen circumference. For all the other body parts, both AN and HC
showed a significant decrease in percentage of misestimation from pre to post illusion.
- Follow-up research shows that after 2 hours and 45 minutes, participants still show changed
perception of body size, especially in the AN group, and for estimates of circumference of the body.
- In the AN group changes in percentage of misestimation at follow-up were found for 3 out of 5 body
parts for which an effect was also found immediately after the FBI (shoulder width, shoulder
circumference and hip circumference).
- In HC, only height and abdomen circumference effects were found, but were not found immediately
after the FBI.
Discussion
Differences in size estimation errors between AN and HC were more profound for body circumference
than body width. AN patients overestimated their body width, but not their height, indicated that they
only experience their body as wider and rounder.
For most body parts of interest the AN and HC group showed decreased misestimation of similar
magnitude. The only exception was that AN patients showed a decrease in circumference estimates
of their abdomen, while in HC this effect was absent. At follow-up, AN patient's size estimates of
shoulder width and circumference had normalized and was no longer different from HC’s. Also the hip
circumference overestimation was decreased. In HC the follow-up effects were smaller. Nevertheless,
AN patients still showed larger percentages of overestimation of body size compared to HC’s.
Changes in body size estimation occured in both synchronous and asynchronous conditions.
According to theoretical models on multimodal bodily experience, embodiment of a fake body part
does not result in the fake body part simply being added to the representation of the body, but in the
fake body part replacing the actual body part in the body representation. In order for the experience of
the body to change, embodiment of a fake body is crucial. The findings in the current study contradict
this reasoning. These findings might result from differences in experimental design. Several studies
suggest that in an immersive VR environment only a first person perspective is sufficient for
embodying an avatar, and that visuo-tactile or visual-motor cues are not a requirement for the FBI but
do strengthen the illusion. Nevertheless, the participants dit not feel embodiment in the asynchronous
condition, which seems to imply that embodiment of an avatar is not crucial for changing the
experience of body size. Perhaps the key element in the current study that caused changed body size
estimation in AN patients was removing visual feedback of the participant’s own body. AN patients
overestimate their body size by about 10% more when they directly perceive their body in a mirror,
compared to making a size estimate from memory. A 10% decline is found from pre to post illusion
estimates. However, we also saw a difference in HC body size estimates, which makes it unlikely that
only the removal of visual information was responsible for changes in body size estimation. Another
possibility is that participants based their size estimates on the most recent visual information that was
provided to them (the body of the avatar). However, there were also size estimation changes in the
shoulders, which were not visible in VR. In addition, also in the follow-up measure changes were
observed. At this moment, participants had access to visual feedback on their actual body size before
they completed the follow-up measure, making the avatar not the most recent-visual input about body
size anymore.
In future research, different avatar sizes can be used. Also, it can be studied if body size estimation
still changes after only providing visual information and no tactile information. In addition, it is
interesting to study why body circumference is more changed in comparison to width: is
circumference more related to conscious experience of body size?. Lastly, it is interesting to assess
subjective body attitudes to gain insight into whether participants emotionally feel different in terms of
size and fatness after the illusion.
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