A Robotic Third Thumb Would Be Handy; The Good News Is That Mostly Anyone Can Learn To Use It Quickly

I might just be able to type faster — and get more articles out (or so my editors would hope) — with this new robotic device made by a British designer and tested by Cambridge University researchers.

Danielle Clode, an augmentation and prosthetics designer, has developed the Third Thumb. It’s a 3D-printed thumb extension for one’s hand that’s controlled through the toes. It’s meant to add to the wearer’s abilities — increasing the range of movement, enhancing their grasping capability, and expanding the carrying capacity of the hand.

“This allows the user to perform tasks that might be otherwise challenging or impossible to complete with one hand or to perform complex multi-handed tasks without having to coordinate with other people,” according to a Cambridge University blog post.

The Third Thumb takes its place on the hand next to the little finger, right across from the biological thumb. A pressure sensor placed under each big toe or foot controls the extra digit. The extent of movement is controlled by the amount of pressure applied, while easing up on the pressure moves the thumb back to its original position.

The design choice to use the hands and feet to operate the device was a good call, given that this same arrangement comes into play while, say, driving a car or playing musical instruments like the piano and drums.

Clode created the wearable third thumb in the mid-2010s while pursuing a Master of Arts programme at the Royal College of Art in London, the United Kingdom (UK). She aimed to explore the relationship between the human body and augmentative and prosthetic technology.

“It is part tool, part experience, and part research; a catalyst and model by which we can better understand human response to artificial extensions,” she explains on her website.

For Clode, the project was an exploration of what it meant to have ability. Typically, prosthetics are associated with disability. However, the Cambridge researcher sought to reframe the use of prosthetics as an extension of existing ability.

The project was inspired by the origin of the word ‘prosthesis’, which means ‘to add, put onto’, and therefore to extend rather than fix or replace, as explained by Clode.

The Third Thumb was put to test on various members of the public at the annual Royal Society Summer Science Exhibition in 2022. The main idea behind the study was to test the motor augmentation technology for its inclusivity.

As many as 597 participants, ranging in age from three to 96 years and hailing from many different places, got to wear the extra digit and use it in tasks. The results of the study were published about a week ago in Science Robotics.

The participants had up to a minute to get to know the device and learn how to use it. Then, they were explained one of two tasks to carry out, both of which involved moving objects — pegs or various foam objects — within 60 seconds.

It turned out that only four of the nearly 600 participants weren’t able to operate the Third Thumb. It was because either the prosthetic didn’t fit their hand securely or they were unable to control the motorised digit with their feet.

As for the tasks, only 13 participants were unable to successfully manipulate objects using the Third Thumb.

Ability levels varied between participants, but not due to gender, left- or right-handedness, or whether someone was ‘good with their hands’. Even age wasn’t a factor, as both the young and old exhibited similar performance.

However, within the elder age group, the performance declined with increasing age. The younger children struggled with the tasks more compared to the older participants. Interestingly, this trend continued up the age ladder as older children (aged 12-16 years) struggled more than young adults.

Importantly, however, mostly anyone was able to learn how to use the robotic digit and then apply that knowledge to carry out tasks. “Our findings offer tangible demonstration of the initial usability of the Third Thumb for a broad demographic,” the paper’s abstract concluded.

“Given the diversity of bodies, it's crucial that the design stage of wearable technology is as inclusive as possible,” Clode has said earlier. “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.”

According to the study’s co-author, Lucy Dowdall, “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.” Dowdall works at the MRC Cognition and Brain Science Unit, University of Cambridge.

Her colleague, Professor Tamar Makin, emphasises the importance of these new beneficial technologies helping those in need. “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.”