Perception of body shape and size without touch or proprioception: evidence from individuals with congenital and acquired neuropathy

Abstract

The degree to which mental representations of the body can be established and maintained without somatosensory input remains unclear. We contrast two “deafferented” adults, one who acquired large fibre sensory loss as an adult (IW) and another who was born without somatosensation (KS). We compared their responses to those of matched controls in three perceptual tasks: first accuracy of their mental image of their hands (assessed by testing recognition of correct hand length/width ratio in distorted photographs and by locating landmarks on the unseen hand); then accuracy of arm length judgements (assessed by judgement of reaching distance), and finally, we tested for an attentional bias towards peri-personal space (assessed by reaction times to visual target presentation). We hypothesised that IW would demonstrate responses consistent with him accessing conscious knowledge, whereas KS might show evidence of responses dependent on non-conscious mechanisms. In the first two experiments, both participants were able to give consistent responses about hand shape and arm length, but IW displayed a better awareness of hand shape than KS (and controls). KS demonstrated poorer spatial accuracy in reporting hand landmarks than both IW and controls, and appears to have less awareness of her hands. Reach distance was overestimated by both IW and KS, as it was for controls; the precision of their judgements was slightly lower than that of the controls. In the attentional task, IW showed no reaction time differences across conditions in the visual detection task, unlike controls, suggesting that he has no peri-personal bias of attention. In contrast, KS did show target location-dependent modulation of reaction times, when her hands were visible. We suggest that both IW and KS can access a conscious body image, although its accuracy may reflect their different experience of hand action. Acquired sensory loss has deprived IW of any subconscious body awareness, but the congenital absence of somatosensation may have led to its partial replacement by a form of visual proprioception in KS.

The role of somatosensation in automatic visuo-motor control: a comparison of congenital and acquired sensory loss

“…directionally tuned responses; Franklin and Wolpert 2008). Perhaps most compelling, however, is recent data from a companion paper (Miall et al 2021), in which we show that KS has shorter verbal reaction times to visual stimuli that appear close to her hands. This, in normal participants, is an unconscious attentional bias to peri-personal space.…”

“…IW was matched with seven controls with a mean age of 67.4 years (SD = 3.63, three males, four females) and KS with seven controls of mean age 38.4 years (SD = 3.71, four males, three females). The experiments reported here were conducted at the same time as others, using the same control groups (Miall et al 2021). Written informed consent was obtained for each participant prior to the study which was approved by the University of Birmingham ethics board, and performed in accordance with the Declaration of Helsinki.…”

“…It should be noted that the 9-hole peg hole test requires distal fine motor skills; the writing and drawing tasks included in the present experiments can be accomplished with more proximal muscles as long as the drawing stylus can be held in a steady grasp. Both KS and IW have deficits in everyday use of their hands (Miall et al 2021) and neither of them handwrite frequently. IW uses a "cross-thumb" grasp for greater stability when holding a pen (Miall et al 2019), while KS uses a wholehand power grip.…”

“…Following control group analyses, we compared the two deafferented participants to their respective control group using Q´ tests (Michael 2007;Renault et al 2018;Bartolo et al 2018;Miall et al 2021). Many tests exist to compare single cases to a group; we chose the Q' test to allow comparison of IW and KS to their separate control groups in a 2 × 3 factorial design (Experiments 1, 2) or 2 × 5 factorial design (Experiment 3).…”

Haptic Perception Training Programs on Fine Motor Control in Adolescents with Developmental Coordination Disorder: A Preliminary Study

“…When performing the movement, the DCD individuals rely mostly on visual or external feedback and have difficulties shifting to an open-loop or feedforward mechanism as they mature [ 6 ]. In contrast, typically developing individuals use visual regard to guide their movements only at early ages and gradually adopt somatosensation instead for more accurate and efficient motor control as maturation takes place [ 7 ].…”