Human-like Prosthetic Hands Rated as ‘Eerie’ by Non-amputees

Researchers from the University of Manchester found non-amputees thought prosthetic hands that resembled real human hands were more “eerie” than mechanical prosthetic hands.

“It has been hypothesized that there is an uncanny valley for hands, such that a hand that is close to being human, but falls short in some way should be perceived as strange or uncanny. The valley refers to a dip in how comfortable people feel about the stimulus, and anecdotally, many people report this experience,” Ellen Poliakoff, PhD, senior lecturer in psychology and co-director of the Body Eyes and Motion (BEAM) lab at the School of Psychological Sciences at the University of Manchester, told O&P Business News. “There has been some experimental research showing that this effect occurs for robotic or computer-generated faces, but our study was the first to explore this effect for hands.”

Prosthetic ratings

Researchers had 43 right-handed participants rate a series of images of hands for eeriness or human-likeness using a 9-point scale from “not at all” to “extremely.” Each image was horizontally flipped and presented, in random order, once as a left hand and once as a right hand.

Study results showed a significant quadratic relationship between human-likeness and eeriness. Researchers found real human hands received the lowest eeriness ratings and the highest ratings for human-likeness, while mechanical hands received intermediate ratings of eeriness and the lowest ratings of human-likeness and prosthetics hands received the highest eeriness ratings, but were rated more human-like vs. mechanical hands. Overall, more human-like hands were rated as less eerie vs. prosthetic and mechanical hands.

“We were surprised to see that one of the prosthetic hands was rated as being highly human-like and received a lower eeriness rating,” Poliakoff said. “We think that at least some of our participants mistook this hand as being a real hand. This is interesting as it suggests that the observer’s belief about the reality of a hand will have a big impact on how they feel about a hand.”

Future research

To help in their research, Poliakoff and colleagues are measuring skin conductance in participants as they view the different types of hands. The advantage of this method is that the participant’s emotional response to the image is measured without asking them directly. Future research should also focus on the effects of movement on individuals’ perceptions of prosthetic hands, as well as how amputees and individuals familiar with prosthetic hands react to seeing a prosthetic limb in comparison with the way the general population reacts.

“Although this study was small-scale and a first step towards looking at this phenomenon, the results suggest that people can find realistic-looking prosthetic hands more uncomfortable to look at than less realistic, clearly mechanical hands. This could have implications for the decisions that prosthetic users make about the type of hand that they wish to use,” Poliakoff said. “We hope that identifying what features of prosthetic hands give rise to a sense of eeriness could guide engineers in designing prosthetic hands.” — by Casey Tingle

For more information:
Poliakoff E. Perception. 2013;doi:10.1068/p7569.

Disclosure: Poliakoff has no relevant financial disclosures.

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