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

Abstract

Body Integrity Identity Disorder (BIID) is a non-psychotic condition wherein individuals desire amputation or paralysis of one or more healthy, fully-functioning limbs (predominantly the legs). Individuals with BIID have been suggested to have a mismatch between the perceived mental representation of the body and its actual physical structure, such that their desired identity matches that of a lower-limb amputee. Accordingly, studies have reported an altered central network involving body representation of the legs in BIID, but its relationship to behavior remains unclear. In the present study, we investigated the integrity of body representation in individuals with BIID, acquired lower-limb amputees, and normally-limbed controls using an online mental rotation task. Participants judged the laterality of left and right foot images presented from different views, orientations, and of different types. We expected BIID participants to be slower for mentally rotating images that corresponded to their affected legs than lower-limb amputees and normally-limbed participants. We found that groups did not significantly differ in their performance. All participants were slower at judging feet presented in awkward postures than natural postures, replicating previous studies and validating our online paradigm. The results are discussed in terms of the robust nature of visual and sensorimotor lower-limb representations, whether related to the self or as prototype, in the context of disturbed lower-limb integrity.

Body representation among adults with phantom limb pain: Results from a foot identification task

“…Similar to previous studies investigating left–right discrimination of feet (Coslett et al, 2010a; Curtze et al, 2010; Stone et al, 2019), task accuracy was high (proportion of correct responses: 0.94, see Table 3 for overall means and Table for model results).…”

“…Findings augment conflicting evidence of body schema impairments post‐LLL. For example our findings support those of Palermo et al (2018), where 14 male participants with LLL were less accurate than 11 controls during a left–right discrimination task, but contrast those of Stone et al (2019) and Curtze et al (2010) who found no differences in left–right discrimination among adults with LLL ( n = 19 and n = 18 respectively) when compared to controls ( n = 33 and n = 18 respectively). While we found significant differences between our moderately sized sample of controls ( n = 37) and adults with LLL ( n = 68), the left–right discrimination task may not be sensitive enough to detect body schema impairments among smaller, heterogeneous samples post‐LLL.…”

“…All participants then completed a left–right foot discrimination task, which was adopted from the protocol reported by Stone et al (2019). Instructions were displayed prior to the task, asking participants to sit comfortably with their prosthesis off (if applicable) and their intact foot (or feet) flat on the floor.…”

“…In each block, 48 foot images were presented twice, in random order, for a total of 96 trials per block. Using an image set from Stone et al (2019) and Curtze et al, (2010) the 48 images included right and left, human and prosthetic feet, presented from the plantar (i.e. bottom‐up) and dorsal (i.e.…”

“…Response time cut‐points were imposed to limit the influence of responses falling outside a realistic response time window (e.g. exceptionally fast responses due to accidental key press, exceptionally slow responses due to distraction) and were based on comparison to prior literature regarding left–right discrimination (Lee et al, 2021; Parsons & Shimojo, 1987; Stone et al, 2019).…”