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.
Highlights
Little is known about how human perception is affected using an upper-limb prosthesis
There was no main effect of group (p > .99), we found a significant Size × Group interaction, F(1.2,32.6) = 9.7, p < .005, ω2 = .11, suggesting that there were differences in the magnitude of the size–weight illusion (SWI) experienced by our different groups
Independent-samples t tests confirmed that the upperlimb amputee group experienced a smaller SWI than controls, t(27) = 3.2, p = .003, d = 1.29, but showed no difference between how these groups experienced a real weight difference, t(27) = 0.20, p = .85, d = 0.08
Summary
Little is known about how human perception is affected using an upper-limb prosthesis. 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. The upper-limb prosthetic users reported a markedly smaller illusion than controls, despite equivalent perceptions of a real mass difference. Despite the critical role that our hands play in this regard, almost no work has examined how the use of an upper-limb prosthesis might affect the hedonic perception of manually acquired properties such as object weight. Top-down explanations, by contrast, suggest that the illusion is a byproduct of how sensory information is combined with prior expectations (Buckingham, 2014) In this context, the small objects feel heavier than weighted larger objects because the lifter expected them to be lighter and subsequently experience a contrast with their prior expectations. What constitutes a prior expectation in this context is, far more contentious (Buckingham, 2014; Buckingham & MacDonald, 2016; Dijker, 2014; Peters, Ma, & Shams, 2016; Vicovaro & Burigana, 2016)
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