News | Friday, 10th May 2019

Eye training helps people use prosthetic hands quicker and with less mental exertion

Dr Greg Wood built a unique prosthetic hand simulator for the study

Amputees and people born without a hand would have a better chance of successfully learning to use a prosthetic hand with a new technique that requires less mental effort and produces better coordination, university academics have found.

Manchester Metropolitan University-led researchers said gaze training, where someone is taught to use their eyes more effectively, produced better results than current rehabilitation methods under which a person is generally encouraged to concentrate on the movement of the artificial limb itself.

The results of the study were published in the Journal of NeuroEngineering and Rehabilitation.

A unique prosthetic hand simulator was purpose built for the study so that able-bodied volunteers could control a myoelectric prosthetic right hand via sensors attached to muscles in their forearm - the same way someone without a hand would have to manipulate a fully articulating prosthesis.

Able-bodied volunteers were chosen so the researchers could compare how their eye and brain activity differed between using the prosthesis and their own anatomical hands while undertaking the same dexterity tasks. The fact the volunteers had not used a myoelectric prosthetic hand meant learning could crucially take place without any prior experience.

Frustrating and mentally fatiguing

Lead academic Dr Greg Wood, Senior Lecturer in Motor Control and Learning at Manchester Metropolitan, said: “Prosthetic users find it extremely difficult to learn how to use a prosthetic hand and they find it frustrating and mentally fatiguing.

“The rejection rate is approximately between 20 per cent and 40 per cent and can be as high as 75 per cent. One of the reasons given for this is that users feel they have to watch the hand as it moves and this requires a lot of mental effort.”

Dr Wood and his team observed how able-bodied participants performed a series of tasks while having their eye movements and neural activity monitored.

Half were taught using gaze training and half with traditional methods.

The early experiments required participants to grasp and lift a jar over an obstacle and to pick up coins from the edge of a desk.

The second exercise, for which participants were not given any directions at all, was the more complex coordination task of making a cup of tea that tested dexterous movements such as dropping a teabag into a mug, lifting and pouring water from a kettle, and stirring the drink with a spoon.

Benefits of gaze training

Dr Wood said: “We wanted to train the eye movements of prosthetic hand users so they mimic those used when a person uses their normal anatomical hand – that is, focusing in on the object they want to pick up rather than consciously fixating on the movement of the hand itself.

“We then compared that to how users performed using typical rehabilitation instructions, which focus on movement control.

“Gaze training, where we trained participants not to look at the hand, made prosthesis users more coordinated and move more effectively, and it also reduced the mental effort involved in using a prosthetic hand.”

The participants who received gaze training completed the coin task 20 per cent quicker than those using traditional instructions and both groups took the same amount of time to make a cup of tea in a transfer task.

But in both instances gaze trained volunteers required significantly less mental exertion, leaving them less fatigued.

It is envisaged these advantages would translate into everyday tasks in the real world.

A new training manual?

The Manchester Metropolitan University team hope their findings spark the development of a new manual for prosthetic hand training that helps remove some of the barriers that lead to prosthetic hand users rejecting their artificial limb, increasing take-up rates.

Dr Wood said: “Currently in this kind of rehabilitation setting there is no standardised instructions.

“The instructions users get are very clinic-based, often drawn from a practitioner’s own experience.

“We have shown that using a gaze training intervention makes people learn quicker and typical instructions that therapists use have a negative effect on the amount of effort needed, in terms of adding to the mental workload.

“We want to revolutionise the rehabilitation process and we hope this work is the first step in this process.”

The prosthetic hand simulator was developed with a grant from the Royal Society.