The impact of using an upper-limb prosthesis on the perception of real and illusory weight differences

Abstract

Little is known about how human perception is affected using an upper-limb prosthesis. To shed light on this topic, we investigated how using an upper-limb prosthesis affects individuals’ experience of object weight. First, we examined how a group of upper-limb amputee prosthetic users experienced real mass differences and illusory weight differences in the context of the ‘size–weight’ illusion. Surprisingly, the upper-limb prosthetic users reported a markedly smaller illusion than controls, despite equivalent perceptions of a real mass difference. Next, we replicated this dissociation between real and illusory weight perception in a group of nonamputees who lifted the stimuli with an upper-limb myoelectric prosthetic simulator, again noting that the prosthetic users experienced illusory, but not real, weight differences as being weaker than controls. These findings not only validate the use of a prosthetic simulator as an effective tool for investigating perception and action but also highlight a surprising dissociation between the perception of real and illusory weight differences.

The perception of real and illusory weight differences with grasping tools

“…The findings from the current study contrast those of Buckingham et al (2018), who demonstrated that individuals who used their regular prosthetic hand/arm to lift SWIinducing objects experienced a smaller weight illusion than controls, with no concomitant reduction in their experience of a difference in physical mass. This unexpected dissociation between real and illusory weight perception was then replicated in a larger group of intact participants lifting the same stimuli with a myoelectric prosthetic hand simulator.…”

“…Although it is not feasible to statistically compare the real and illusory weight differences experienced with a prosthetic simulator to those experienced with a tool due to differences in mass and volume of the stimuli between these studies, we can offer some pertinent observations. First, E2 from Buckingham et al (2018) demonstrated that individuals using a prosthetic hand simulator experienced a smaller SWI than individuals using their anatomical hand, with a p value < .000001a highly significant effect -using a between-group design. By contrast, the equivalent test in the current study yielded a p value of .11, despite having over double the number of participants and a repeated measures design, which typically yields higher power to detect an experimental effect than a between-group design.…”

“…To better visualize these data at an individual level, and compared to previous studies of this nature (Buckingham et al, 2018), we quantified the magnitude of each participant's experience of the SWI and the real-weight difference. To quantify the SWI, we subtracted each participant's average rating given to the smallest objects from their average rating given to the large objects in each condition.…”

“…Indeed, active tool has even been shown to have a direct impact on somatosensory processing during object interaction (Miller, Longo, & Saygin, 2019). In terms of weight perception, Buckingham et al (2018) examined how the SWI manifests when using a prosthetic handa unique form of tool use. Of particular relevance was the second experiment (E2), where intact individuals who lifted the illusion-inducing stimuli with a myoelectric prosthetic simulator which they wore over their anatomical hand.…”

Visual attention, EEG alpha power and T7-Fz connectivity are implicated in prosthetic hand control and can be optimized through gaze training

“…First, we are limited by our use of intact users of a simulator rather than patients with limb loss. However, evidence has shown that these populations display comparable kinematic profiles [1], visuomotor behaviours [6,7], and perceptual experiences [62], suggesting that using a simulator provides a useful surrogate to examine the sensory-motor deficits that prosthesis users face. Yet, it is unclear how increasing the length of the operating arm when using the prosthesis simulator (approximately 7 cm when the hand is unclenched) independently influences visuomotor and neurophysiological behaviours.…”