Ever wanted an extra thumb? Well, now you can!

31st May 2024
Harry Fowle

Alongside Cambridge University, members of the public were able to learn quickly how to use a third thumb – a controllable, prosthetic extra thumb – to pick up and manipulate objects.

Researchers from Cambridge University tested this robotic device on a wide variety of participants, aiming to ensure the inclusivity and effectiveness of new technologies across different demographics.

Motor augmentation, a developing field of technology, involves using motorised wearable devices such as exoskeletons or additional robotic body parts to enhance human capabilities beyond natural limitations.

These devices could significantly boost the productivity of healthy individuals, while also offering new ways for people with disabilities to interact with their environment.

Professor Tamar Makin from the Medical Research Council (MRC) Cognition and Brain Sciences Unit at the University of Cambridge remarked: “Technology is changing our very definition of what it means to be human, with machines increasingly becoming a part of our everyday lives, and even our minds and bodies.

"These technologies open up exciting new opportunities that can benefit society, but it’s vital that we consider how they can help all people equally, especially marginalised communities who are often excluded from innovation research and development.

“To ensure everyone will have the opportunity to participate and benefit from these exciting advances, we need to explicitly integrate and measure inclusivity during the earliest possible stages of the research and development process.”

Dani Clode, a collaborator in Professor Makin’s lab, developed the Third Thumb, a robotic thumb designed to increase the wearer’s range of motion, enhance their grasping ability, and expand the hand’s carrying capacity. This enables users to perform tasks that might be difficult or impossible with one hand or to complete complex multi-handed tasks without needing assistance from others.

The Third Thumb is worn on the opposite side of the palm from the biological thumb and is controlled by pressure sensors placed under the big toes. Pressure from the right toe moves the Thumb across the hand, while pressure from the left toe moves it toward the fingers. The movement of the Thumb is proportional to the pressure applied, and releasing the pressure returns it to its original position.

In 2022, the team showcased the Third Thumb at the Royal Society Summer Science Exhibition, where people of all ages had the chance to try it out. The findings have been published in Science Robotics.

Over five days, the team tested 596 participants, aged three to 96, from various demographic backgrounds. Only four participants were unable to use the Third Thumb, either due to an improper fit or difficulty controlling it with their feet (the exhibition-specific pressure sensors were not suitable for very lightweight children).

Participants had up to a minute to familiarise themselves with the device while the team explained how to perform one of two tasks.

In the first task, participants used the Third Thumb to pick up pegs from a pegboard and place them in a basket within 60 seconds. 333 participants completed this task.

In the second task, participants used both the Third Thumb and their biological hand to manipulate and move foam objects of various shapes, requiring different manipulations to increase task dexterity. Again, participants aimed to move as many objects as possible into the basket within 60 seconds. 246 participants completed this task.

Nearly all participants adapted to the device immediately. 98% successfully manipulated objects using the Third Thumb within the first minute, with only 13 unable to complete the task.

While participant skill levels varied, there were no significant differences between genders or handedness – despite the Thumb always being worn on the right hand. There was no clear evidence that individuals with manual dexterity skills, such as musicians or those in manual professions, performed better at the tasks.

Both older and younger adults showed similar abilities in using the new technology, though performance within the older age bracket declined with age. Researchers attributed this to the general decline in sensorimotor and cognitive abilities associated with ageing and possibly a generational familiarity with technology.

Younger children generally performed worse, with six out of the 13 participants who could not complete the task being under ten years old. Among those who did complete it, the youngest children performed worse compared to older children. Even children aged 12-16 struggled more than young adults.

Dani Clode commented: “Augmentation is about designing a new relationship with technology—creating something that extends beyond being merely a tool to becoming an extension of the body itself.

"Given the diversity of bodies, it’s crucial that the design stage of wearable technology is as inclusive as possible. It’s equally important that these devices are accessible and functional for a wide range of users. Additionally, they should be easy for people to learn and use quickly.”

Co-author Lucy Dowdall, also from the MRC Cognition and Brain Science Unit, added: “If motor augmentation – and even broader human-machine interactions – are to be successful, they’ll need to integrate seamlessly with the user’s motor and cognitive abilities.

"We’ll need to factor in different ages, genders, weight, lifestyles, disabilities – as well as people’s cultural, financial backgrounds, and even likes or dislikes of technology. Physical testing of large and diverse groups of individuals is essential to achieve this goal.”

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