The self-perceived body size in obesity: Evidence from the implicit representation of the hand

Abstract

To locate our body in the space, we rely on an implicit representation of body size and shape: the body model. Evidence about the implicit representation of bodily dimensions in obesity is rare. Nevertheless, it seems to suggest that such representation is not altered in obesity compared to healthy weight individuals. To probe further this hypothesis, we investigated the implicit representation of hand dimensions with a landmark localisation task, comparing individuals with obesity and healthy weight individuals. Furthermore, as body model distortions may be related to tactile acuity, the tactile acuity threshold was measured using a two-point discrimination task. In accordance with the previous evidence, we observed that healthy weight participants showed a significant underestimation of finger length and overestimation of hand width. Interestingly, comparable body model distortions were shown also in participants with obesity. No differences in tactile acuity emerged between the two groups; also, when considering the whole sample, as tactile acuity decreases hand width overestimation increases. Thus, obesity seems to have no effect on the characteristics of the body model relative to the hand. Accordingly, the physiological mechanisms supporting the development of the implicit representation of hand dimensions in the healthy weight population may be preserved in obesity.

Behavioural evidence of altered sensory attenuation in obesity

“…Moreover, we reported that our controls showed a higher SA effect, as suggested by the positive SA index, in comparison with the participants with obesity, exhibiting a negative SA index. As we did not observe any difference in the tactile threshold between our samples, in line with other recent evidence (Tagini et al, 2021a), our results were unlikely to be explained by the intensity of the peripheral stimulation.…”

“…Eighteen participants affected by obesity were recruited during the first week of a diagnostic recovery in the IRCCS Istituto Auxologico Italiano, Ospedale San Giuseppe (Piancavallo, Italy). In line with previous studies (Scarpina et al, 2016(Scarpina et al, , 2019a(Scarpina et al, , 2019bTagini et al, 2020aTagini et al, , 2020bTagini et al, , 2021a, only participants with a body mass index (i.e., BMI) over the value of 30 (i.e., indicating obesity, World Health Organization, 2000) were included. We excluded individuals with any neurological symptoms/signs, especially of neuropathic pain, according to the clinical assessment.…”

“…Scarce and not conclusive evidence addressing body ownership had been reported (Scarpina et al, 2019b;Tagini et al, 2020aTagini et al, , 2021a in obesity. A recent work by Tagini and colleagues (2020a) compared the susceptibility of individuals affected by obesity to the well-known Rubber Hand Illusion (Botvinick & Cohen, 1998, that is, an experimental procedure leading individuals to feel as if a rubber hand was part of their own body) with a sample of healthy-weight individuals.…”

Does physical weight alter the mental representation of the body? Evidence from motor imagery in obesity

“…While in Scarpina and colleagues (2017) participants were induced to think they were performing a memory task, and hence relying on a more implicit motor imagery strategy to perform actions, in Guardia and colleagues (2013) the participant explicitly imagined to perform the movement before the real action. Interestingly, the role of strategy in obesity is evident in other tasks involving the body, but not actions: as reported in a recent review , affected individuals traditionally show an altered mental representation of their own physical dimensions when they are explicitly asked to judge them (i.e., Scarpina et al, 2014Scarpina et al, , 2017Schwartz & Brownell, 2004); however, they describe the same features accurately when the processes are implicit (as in Tagini, Scarpina, Scacchi, et al, 2021). It is worth to note that both Guardia and colleagues (2013) and Scarpina and colleagues (2017) tested an obstacleavoidance action, a walking through door-like openings).…”

Spatial hand representation in anorexia nervosa: a controlled pilot study

“…Different experimental paradigms have been used to investigate various aspects of body representation such as the rubber hand illusion 12 , localization task based on tactile or verbal instructions as described above 10 , 11 , 13 or indirect behavioural measures 14 .…”