Summary: University of Exeter researchers report people with prosthetic arms are not able to experience the ‘size-weight’ illusion as strongly as those without missing limbs.
Source: University of Exeter.
People with prosthetic arms or hands do not experience the “size-weight illusion” as strongly as other people, new research shows.
The size-weight illusion, which affects about 98 per cent of people, causes them to experience smaller objects as feeling heavier than larger objects of the same weight.
The study – led by the University of Exeter and the University of Strathclyde – compared the perception of people using their anatomical hands with that of amputees using prosthetic limbs.
The researchers were surprised to find that the size-weight illusion was twice as strong in non-amputees lifting with their hand as it was in the prosthetic users.
“This unexpected finding suggests that using a prosthesis might fundamentally affect the way people perceive the world,” said Dr Gavin Buckingham of the Department of Sport and Health Sciences at the University of Exeter.
“People using a prosthetic hand perceive real weight differences just like everybody else, but the effect of the size-weight illusion is halved.
“The reasons for this are a little mysterious. It might be to do with the lack of sensory receptors in a prosthetic hand, or might depend on how the prosthetic hand is attached to the stump.”
In a second experiment, the researchers tested how the illusion affected non-amputees who used a prosthetic hand simulator to lift objects.
The results were similar to those for amputees with prosthetic limbs – the effect of the size-weight illusion was halved.
Sarah Day, of the National Centre for Prosthetics and Orthotics in the Department of Biomedical Engineering at the University of Strathclyde, added: “Many amputees prefer not to use prosthetic arms or hands, but the reasons for this are not well understood. Research like this might help us better understand why.”
[cbtabs][cbtab title=”MLA”]University of Exeter “People with Prosthetic Arms Less Affected by Common Illusion.” NeuroscienceNews. NeuroscienceNews, 22 January 2018. <https://neurosciencenews.com/prosthetic-arms-illusion-8342/>.[/cbtab][cbtab title=”APA”]University of Exeter (2018, January 22). People with Prosthetic Arms Less Affected by Common Illusion. NeuroscienceNews. Retrieved January 22, 2018 from https://neurosciencenews.com/prosthetic-arms-illusion-8342/[/cbtab][cbtab title=”Chicago”]University of Exeter “People with Prosthetic Arms Less Affected by Common Illusion.” https://neurosciencenews.com/prosthetic-arms-illusion-8342/ (accessed January 22, 2018).[/cbtab][/cbtabs]
The impact of using an upper-limb prosthesis on the perception of real and illusory weight differences
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.