When less is more – Implicit preference for incomplete bodies in xenomelia

Abstract

Individuals with xenomelia identify with an amputated rather than with their physically complete, healthy body. They often mimic amputees and show a strong admiration of and sexual attraction towards them. Here we investigated for the first time empirically whether such unusual preference for amputated bodies is present also on an implicit level. Using the well-validated Implicit Association Test we show that individuals with xenomelia manifested a stronger implicit and explicit preference for amputated bodies than a normally-limbed control group and a group of involuntary amputees did. Interestingly, the two latter groups did not differ in their implicit and explicit preference for complete versus amputated bodies. These findings are an important step in understanding how deeply rooted attitudes about a socially normative body appearance may be influenced by a developmentally disordered experience of one's own bodily self. We conclude that this is the first behavioral evidence demonstrating a conflict of self-identification on an implicit level and this enriches current understandings of xenomelia as a primarily neurological disorder. AbstractIndividuals with xenomelia identify with an amputated rather than with their physically complete, healthy body. They often mimic amputees and show a strong admiration of and sexual attraction towards them. Here we investigated for the first time empirically whether such unusual preference for amputated bodies is present also on an implicit level. Using the wellvalidated Implicit Association Test we show that individuals with xenomelia manifested a stronger implicit and explicit preference for amputated bodies stronger than a normally-limbed control group and a group of involuntary amputees did. Interestingly, the two latter groups did not differ in their implicit and explicit preference for complete versus amputated bodies. These findings are an important step in understanding how deeply rooted attitudes about a socially normative body appearance may be influenced by a developmentally disordered experience of one's own bodily self. We conclude that this first behavioral evidence to demonstrate a conflict of self-identification on an implicit level and this enriches current understandings of xenomelia as a primarily neurological disorder.

Mental rotation of feet in individuals with Body Integrity Identity Disorder, lower-limb amputees, and normally-limbed controls

“…Individuals with this condition, particularly those who desire amputation of a limb, describe themselves as "overcomplete" and as though the limb does not belong to them, experiencing a sense of (non-delusional) disownership over the body part. While research is scant on this subject, it has been growing in recent years [3][4][5][6][7]. The condition manifests before adolescence, usually affects males, and the desire to amputate/paralyze is usually directed towards the lower limbs [2,8].…”

“…Though, few studies have examined the behavioural outcome of these altered (or poorly established) body representations. Recently, Macauda and colleagues [6] explored the implicit (via an implicit association task) and explicit (via a questionnaire) attitudes about amputated and non-amputated bodies in a sample of BIID participants, lower-limb amputees, and normally-limbed control participants. They showed that BIID participants have a stronger implicit and explicit preference for amputated bodies, when compared to amputees and normallylimbed controls.…”

An Investigation of Lower Limb Representations Underlying Vision, Touch, and Proprioception in Body Integrity Identity Disorder

“…Finally, this is the first study, to our knowledge, that has tested amputation-and paralysis-variant BIID participants involving behavioral measurements. All of the behavioral studies on BIID, to date, have been in those who desire amputation (5,7,8,100). A few questionnaire-based investigations of BIID have included paralysis-variant participants (4,6,101) and only one neuroimaging study included paralysis-variant participants (n = 2) in addition to amputation-desire participants (n = 6; 12).…”

“…This can include the (lesser known) variant which involves the desire for deafness (2) or blindness (3), but most reported cases of BIID involve the desire to amputate or paralyze one or more healthy limbs [e.g. (2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)]. People with this variant of BIID (who will be the focus of the current report) presumably experience a mismatch between their internal mental image of the body and the external physical and functional boundaries of the body itself (4,13).…”

“…Yet, few behavioral studies have investigated the manifestation of this disordered body representation in BIID individuals. We know that, at least for the amputation-variant, these individuals have an implicit preference for amputated versus intact bodies (7), have a more vivid rubber foot illusion for the affected foot (8), show impaired temporal-spatial processing of tactile stimuli for the affected leg (5), have an increased skin conductance response (SCR) to stimuli contacting the affected (but not the unaffected) limb (9,28), and a reduced SCR response to stimuli approaching the affected limb (28). These studies, in conjunction with the neuroimaging results, do suggest that the origins of BIID might be a consequence of disturbed integration of bottom-up information (like vision, touch, proprioception) with top-down information, like higher order model(s) of the affected body part.…”