Anouk Keizer

Tactile body image disturbance in anorexia nervosa

Body image disturbances are central to anorexia nervosa (AN). Previous studies have focused mainly on attitudinal and visual aspects. Studies on somatosensory aspects thus far have been scarce. We therefore investigated whether AN patients and controls differed in tactile perception, and how this tactile body image related to visual body image and body dissatisfaction. The Tactile Estimation Task (TET) measured tactile body image: Two tactile stimuli were applied to forearm and abdomen, and, while blindfolded, participants estimated the distance between the two tactile stimuli between their thumb and index finger. The Distance Comparison Task (DCT) measured visual body image. Compared to controls (n=25), AN patients (n=20) not only visualized their body less accurately, but also overestimated distances between tactile stimuli on both the arm and abdomen, which might reflect a disturbance in both visual and tactile body image. High levels of body dissatisfaction were related to more severe inaccuracies in the visual mental image of the body, and overestimation of tactile distances. Our results imply that body image disturbances in AN are more widespread than previously assumed as they not only affect visual mental imagery, but also extend to disturbances in somatosensory aspects of body image.

Too Fat to Fit through the Door: First Evidence for Disturbed Body-Scaled Action in Anorexia Nervosa during Locomotion

To date, research on the disturbed experience of body size in Anorexia Nervosa (AN) mainly focused on the conscious perceptual level (i.e. body image). Here we investigated whether these disturbances extend to body schema: an unconscious, action-related representation of the body. AN patients (n = 19) and healthy controls (HC; n = 20) were compared on body-scaled action. Participants walked through door-like openings varying in width while performing a diversion task. AN patients and HC differed in the largest opening width for which they started rotating their shoulders to fit through. AN patients started rotating for openings 40% wider than their own shoulders, while HC started rotating for apertures only 25% wider than their shoulders. The results imply abnormalities in AN even at the level of the unconscious, action oriented body schema. Body representation disturbances in AN are thus more pervasive than previously assumed: They do not only affect (conscious) cognition and perception, but (unconscious) actions as well.

Aberrant somatosensory perception in Anorexia Nervosa

Anorexia Nervosa (AN) patients have a disturbed experience of body size and shape. Previously it has been shown that these body representation disturbances extend to enlarged perception of tactile distances. Here we investigated whether misperception of tactile size could be related to inaccurate elementary somatosensory perception. Tactile size perception was measured with the Tactile Estimation Task (TET) (see Keizer et al., 2011). Elementary somatosensory perception was assessed with a pressure detection task and two point discrimination (TPD). Compared to controls (n=28), AN patients (n=25) overestimated tactile size, this effect was strongest for the abdomen. Elementary tactile perception deviated in AN as well: Patients had a lower threshold for detecting pressure on their abdomen, and a higher threshold for TPD on both the arm and abdomen. Regression results implied that group membership predicted tactile size estimation on the arm. Both group membership and TPD predicted tactile size estimation on the abdomen. Our results show that AN patients have a disturbance in the metric properties of the mental representation of their body as they overestimate the size of tactile stimuli compared to controls. Interestingly, AN patients and controls differ in elementary somatosensory perception as well. However, this could not solely explain misperception of tactile distances, suggesting that both bottom-up and top-down processes are involved.

Does the experience of ownership over a rubber hand change body size perception in anorexia nervosa patients

Anorexia nervosa (AN) patients show disturbances in body size experience. Here, malleability of body representation was assessed by inducing the Rubber Hand Illusion (RHI). Specifically the impact of the illusion on body size estimation was investigated. Thirty AN patients and thirty healthy females participated. The RHI was induced synchronously (experimental condition) and asynchronously (control condition) Both before and after induction of the RHI participants were asked to estimate the size of their own and the rubber hand. The results showed that AN patients had a stronger experience of ownership over the rubber hand than healthy females in the experimental, but not the control condition. AN patients and HC did not differ on proprioceptive drift. Before induction of the illusion AN patients overestimated hand width. After induction of the illusion (experimental as well as control condition) AN patients no longer overestimated the width of their hand. Healthy females correctly estimated hand size both before and after induction of the RHI. In conclusion, stronger experience of ownership over the rubber hand in the AN group implies a more malleable body representation in AN patients compared to healthy females. Changed hand size estimation in the AN group appears to be unrelated to the RHI, as it occurred under both experimental and control conditions of the illusion. Alternative interpretations are discussed.

A Virtual Reality Full Body Illusion Improves Body Image Disturbance in Anorexia Nervosa

Background Patients with anorexia nervosa (AN) have a persistent distorted experience of the size of their body. Previously we found that the Rubber Hand Illusion improves hand size estimation in this group. Here we investigated whether a Full Body Illusion (FBI) affects body size estimation of body parts more emotionally salient than the hand. In the FBI, analogue to the RHI, participants experience ownership over an entire virtual body in VR after synchronous visuo-tactile stimulation of the actual and virtual body. Methods and Results We asked participants to estimate their body size (shoulders, abdomen, hips) before the FBI was induced, directly after induction and at ~2 hour 45 minutes follow-up. The results showed that AN patients (N = 30) decrease the overestimation of their shoulders, abdomen and hips directly after the FBI was induced. This effect was strongest for estimates of circumference, and also observed in the asynchronous control condition of the illusion. Moreover, at follow-up, the improvements in body size estimation could still be observed in the AN group. Notably, the HC group (N = 29) also showed changes in body size estimation after the FBI, but the effect showed a different pattern than that of the AN group. Conclusion The results lead us to conclude that the disturbed experience of body size in AN is flexible and can be changed, even for highly emotional body parts. As such this study offers novel starting points from which new interventions for body image disturbance in AN can be developed.

A Novel Technique for Improving Bodily Experience in a Non-operable Super–Super Obesity Case

Introduction: The available clinical guidelines for super-super obese patients (i.e., with body mass index (BMI) > 60 kg/m2) that are not suitable for bariatric surgery mandate a palliative multidisciplinary treatment (i.e., production and maintenance of weight loss) provided in a center of excellence. However, the modality and the impact of this approach are still controversial. Moreover, it is not able to address the high level of body dissatisfaction and body distortions that are common among these patients. Clinical Presentation: We report the case of a non-operable super–super obesity – a 37 year old woman with a BMI of 62 kg/m2 – receiving a specialized treatment for her obstructive sleep apnea. She entered a multidisciplinary program that promoted healthy behaviors, including physical activities and psychological intervention. To improve body dissatisfaction, which was linked to a significant multisensory impairment of body perception, she also entered a virtual reality (VR) body-swapping illusion protocol. At the end of the current investigation, the patient continued her multidisciplinary program, reporting an increase in the motivation for undertaking healthy behavior and a decrease in the anxiety feelings associated with her clinical condition. Conclusion: This case provides preliminary evidence that both body dissatisfaction and body-size distortions of non-operable super-super obesity patients could be addressed by a VR body-swapping protocol, which is important because the palliative multidisciplinary treatment recommended for these patients is not able to address them. Interestingly, the use of a VR body-swapping illusion protocol seems to be able to improve not only the experience of the body in these patients but their motivation for change, too.

No consistent cooling of the real hand in the rubber hand illusion

In the rubber hand illusion (RHI), participants view a rubber hand that is stroked synchronously with their real, hidden hand. This procedure results in experiencing an increased sense of ownership over the rubber hand and demonstrates how multisensory information (vision, touch) can influence the sense of body ownership. However, it has also been suggested that a (lack of) sense of ownership over an own body part may in turn influence bodily processes. This suggestion has previously been supported by the observation that a decrease in skin temperature in the real hand correlated with ownership over the rubber hand. However, this finding has not been consistently replicated. Our lab has conducted several studies in which we recorded temperature of the hands during the RHI using various measures and in different circumstances, including continuous temperature measurements in a temperature-controlled room. An overall analysis of our results, covering five attempts to replicate the traditional RHI experiment and totalling 167 participants, does not show a reliable cooling of the real hand during the RHI. We discuss this failure to replicate and consider several possible explanations for inconsistencies between reports of hand temperature during the RHI.

Body representation disturbances in visual perception and affordance perception persist in eating disorder patients after completing treatment

Body image disturbances (BID) are a key feature of eating disorders (ED). Clinical experience shows that BID exists in patients who Completed their Eating Disorder Treatment (CEDT), however studies concerning BID in CEDT patients are often limited to cognition and affect, measured by interviews and questionnaires. The current study is the first systematic study investigating the full scope of the mental body representation, including bodily attitudes, visual perception of body size, tactile perception, and affordance perception in CEDT patients. ED patients (N = 22), CEDT patients (N = 39) and healthy controls (HC; N = 30) were compared on BID tasks including the Body Attitude Test (BAT), Visual Size Estimation (VSE), Tactile Estimation Task (TET), and Hoop Task (HT). Results on the BAT show higher scores for ED patients compared to CEDT patients and HC but no difference between CEDT patients and HC. Both ED and CEDT patients show larger overestimations on the VSE and HT compared to HC, where ED patients show the largest overestimations. No group differences were found on the TET. The results indicate the existence of disturbances in visual perception and affordance perception in CEDT patients. Research focussing on more effective treatments for ED addressing multiple (sensory) modalities is advised.

The influence of vision, touch, and proprioception on body representation of the lower limbs

Numerous studies have shown that the representation of the hand is distorted. When participants are asked to localize unseen points on the hand (e.g. the knuckle), it is perceived to be wider and shorter than its physical dimensions. Similar distortions occur when people are asked to judge the distance between two tactile points on the hand; estimates made in the longitudinal direction are perceived as significantly shorter than those made in the transverse direction. Yet, when asked to visually compare the shape and size of ones own hand to a template hand, individuals are accurate at estimating the size of their own hands. Thus, it seems that body representations are, at least in part, a function of the most prominent underlying sensory modality used to perceive the body part. Yet, it remains unknown if the representations of other body parts are similarly distorted. The lower limbs, for example, are structurally and functionally very different from the hands, yet their representation(s) are seldom studied. What does the body representation for the leg look like? And is leg representation dependent on which sense is probed when making judgments about its shape and size? In the current study, we investigated what the representation of the leg looks like in visually-, tactually-, and proprioceptively-guided tasks. Results revealed that the leg, like the hand, is distorted in a highly systematic manner. Distortions seem to rely, at least partly, on sensory input. This is the first study, to our knowledge, to systematically investigate leg representation in healthy individuals.

Walking through Apertures: Do You Know What You are Doing during Body-Scaled Action?:

We investigated whether body-scaled action is influenced by awareness of task performance. Participants walked through apertures varying in size. Awareness of performing the action was manipulated by asking half of the participants to concurrently perform a haptic memory task. Distracted participants showed a smaller maximum amount of shoulder rotation at A/Scrit. Walking through apertures thus seems a rather automatic/uniform process regarding action planning, but being distracted from performing the action appears to influence how the action is performed, and may increase its efficiency.