Whole-hand perceptual maps of joint location

Abstract

Hands play a fundamental role in everyday behaviour. Nevertheless, healthy adults show striking misrepresentations of their hands which have been documented by a wide range of studies addressing various aspects of body representation. For example, when asked to indicate the location within the hand of the knuckles, people place them substantially farther forward than they actually are. Previous research, however, has focused exclusively on the knuckles at the base of each finger, not considering the other knuckles in the fingers. This study therefore aimed to investigate conceptual knowledge of the structure of the whole hand, by investigating judgements of the location of all 14 knuckle joints in the hand. Participants localised each of the 14 knuckles of their own hand (Experiment 1) or of the experimenter's hand (Experiment 2) on a hand silhouette.We measured whether there are systematic localisation biases. The results showed highly similar pattern of mislocalisation for the knuckles of one's own hand and those of another person's hand, suggesting that people share an abstract conceptual knowledge about the hand structure. In line with previous reports, we showed that the metacarpophalangeal joints at the base of the fingers are judged as substantially father forward in the hand than they actually are. Moreover, for the first time we showed a gradient of this bias, with progressive reduction of distal bias from more proximal to more distal joints. In sum, people think their finger segments are roughly the same, and that their fingers are shorter than they are.

The characteristics of the implicit body model of the trunk

“…A subsequent study using the same methodology also reported participants overestimated the width of the torso, although participants also overestimated torso length, which differs from the current study ( Fuentes et al, 2013a ). For height, if considering the trunk overall with thorax-to-hips height, participants tended to underestimate their trunk in the vertical axis, consistent with previous findings of underestimation in length or proximo-distal direction, for the hand ( Cocchini et al, 2018 ; Longo, 2017b , 2018 ; Longo & Haggard, 2010 , 2012a , 2012b ; Longo & Holmes, 2020 ; Longo et al, 2015b ; Mattioni & Longo, 2014 ; Myga et al, 2021 ; Peviani & Bottini, 2020 ; Saulton et al, 2015 , 2016 , 2017 ; Tamè et al, 2017 ), face ( Fuentes et al, 2013c ) and leg ( Stone et al, 2018 ).…”

“…Investigators have attempted to map the body model by asking participants to localise the position of body landmarks without the use of visual information. These studies have all yielded results showing systematic distortions of the body model at the hand ( Ambroziak et al, 2018 ; Cocchini et al, 2018 ; Longo, 2015b , 2017b , 2018 ; Longo & Haggard, 2010 , 2012a , 2012b ; Longo & Holmes, 2020 ; Longo et al, 2015b ; Margolis & Longo, 2015 ; Mattioni & Longo, 2014 ; Myga et al, 2021 ; Peviani & Bottini, 2020 ; Saulton et al, 2015 , 2016 , 2017 ; Tamè et al, 2017 ), the forearm ( Longo, 2017b ), face ( Fuentes et al, 2013c ; Longo & Holmes, 2020 ; Mora et al, 2018 ) and leg ( Stone et al, 2018 ).…”