What would you do with a robotic third thumb?

Testers can already open bottles, crack eggs, and even play guitar.
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Researchers want to ensure the Third Thumb is intuitive to use and accessible to wide ranges of people. Dani Clode Design / The Plasticity Lab

Take a moment to imagine what unheard sounds famed psychedelic rock guitarist Jimi Hendrix could have conjured to existence if he had an extra digit to work with. By that same measure, consider how much faster historic painters like Frida Kahlo or Vincent Van Gogh could have amassed their life’s work if they could have simply held their oil and brush in the same hand. Each of those artists were limited by the constraints of their biological anatomy but that might not necessarily be the case for future creators thanks to a new, 3D-printed robotic wearable, aptly called the “The Third Thumb.” The thumb, which is part of a growing field of technology referred to as “wearable motor augmentation,” is being designed to enhance users’ biological capabilities with an eye toward ensuring accessibility and equal access.

Credit: Dani Clode Design / The Plasticity Lab

How does the Third Thumb work?

The Third Thumb, created by University of Cambridge augmentation and prosthetics designer Dani Clode, is a 3D-printed robotic thumb controlled by a user’s toes. Once equipped via a wrist strap, the robotic digit sits on the side of a palm opposite of a user’s biological thumb and resembles a sixth, elongated finger. Users operate the thumb by pressing down on a pair of sensors underneath each big toe. Pressure applied by the right toe moves The Third Thumb side to side, while pressure from the left toe moves it up and down. The controls are wireless and proportional, so faster movement form the toes will result in similarly quick movement with the thumb. Easing up on toe pressure will release the thumb back to its original position. 

Researchers believe this mechanical thumb could soon assist people who have lost a limb regain mobility and functionality. But The Third Thumb’s possible uses aren’t only limited to aiding users with lost fingers. Eventually, researchers believe it could enhance biological functioning broadly so that wearers can complete tasks that would ordinarily be difficult or impossible to perform with a thumb and four fingers. Researchers exploring wearable motor automation, which can include sci-fi-esque exoskeleton suits and complex mechanical limbs, believe these tools can eventually increase both productivity and safety. 

Though the initial design for The Third Thumb dates back to 2017, University of Cambridge researchers released the results of its first large scale round of human testing with the device this week as part of a paper published in the journal Science Robotics. The researchers took large and small versions of the device to the 2022 Royal Society Summer Science Exhibition, where they tested it on 596 people over the course of five days. Participants in the experiment ranged in ages from 3-96 years old and similarly varied in terms of gender, ethnicity, and handedness. Armed with the groups of willing volunteers, researchers set out to determine whether or not this wide range of people could easily comprehend and effectively use the thumb. 

Credit: Dani Clode Design / The Plasticity Lab

An overwhelming majority of testers found the Third Thumb easy to use 

In their testing, the research emphasized the importance of teaching patricants to use the device quickly, and intuitively. Lucy Dowdall, one of the paper’s co-authors, said wearable devices like The Third Thumb and even more intensive brain computer interfaces like the one currently being developed by Elon Musk’s Neuralink will crucially need to “integrate seamlessly” with a user’s motor and cognitive functions if they are ever want to gain traction. 

“We were really interested in this research at looking at how good are people initially picking up that initial motor skill,” Dowdall said. “So in the first few moments of usage, can they really use the Third Thumb.”

The results of the experiment were encouraging. Nearly all (98%) of the participants were able to successfully equip the Third Thumb and manipulate objects within the first minute of wearing it. But simply moving objects and doing so proficiently are different stories altogether. To test the latter, the researchers put the patricants through two separate tests. First, researchers asked the participants to use their new digit to grasp pegs from a pegboard and place them in a basket within 60 seconds. More than half (333) completed the task. Next, the testers were asked to use the thumb alongside their other fingers to try and snatch onto a variety of foam objects that required various levels of dexterity to hold and similarly place them in the basket. This time, 246 of the participants completed the test. 

“We were surprised by just how good everyone was, particularly in the exhibition setting but also the broad age range we have,” Dowdall added. “Everyone could perform a task well.” 

Credit: Dani Clode Design / The Plasticity Lab

Researchers want want to instill accessibility early in the design process  

The researchers note they were encouraged not just by the sheer amount of participants able to use the thumb, but also their wide demographic variety. Users of all ages were able to successfully use the thumb quickly, to some degree. Similarly, the researchers say they measured no noticeable difference in overall performance between genders or between left and right handed people. That ease of use across biological differences is crucial, the researchers note, to help prevent one group or subgroup from disproportionately benefiting from the technology gaining an unfair advantage. Though that concern might seem premature for still relatively nascent biological limb technology, the researchers are aiming to try and build in ethical and equity considerations from the ground up.

“Given the diversity of bodies, it’s crucial that the design stage of wearable technology is as inclusive as possible,” Clode said in a statement. “It’s equally important that these devices are accessible and functional for a wide range of users.”

Recent novel technologies are filled with counter examples where those same considerations weren’t properly stressed. From augmented reality and automated speech detection systems that struggle to work properly for people of color, to car safety standards prioritized for “average” male bodies, technology is awash with instances of seemingly benign design overlooks leading to potentially unequal effects for certain groups down the line. Researchers want to try and avoid replicating those outcomes with The Third Thumb. 

Credit: Dani Clode Design / The Plasticity Lab

“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 marginalized communities who are often excluded from innovation research and development,” University of Cambridge Professor Tamar Makin said in a statement. “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.”

Though the test subjects at Royal Society Summer Science Exhibition were largely limited to moving blocks and foam, researchers have already provided glimpses at The Third Thumb’s more handy potential. In videos and photos demonstrating the tests, users have shown the thumb is strong enough to squeeze fruit but precise enough to pinch thread with another finger. Elsewhere, researchers can be seen cracking one egg while nestling another safely on the thumb. Another photo shows a painter holding a cup full of ink with the thumb while using a gripping motion in that same hand to manipulate a paintbrush. And yes, the thumb can also apparently be used to fret chords on a guitar.

Clode, the Third Thumb’s creator, admitted learning how to use the device can seem “quite weird” for people who’ve lived their lives with 10 digits and two thumbs. That said, the most recent research suggests looks can be deceiving.

“What’s really exciting about the Thumb is that it seems quite complex from the beginning and it’s really not,” Clode said. “People can quickly and easily use it within one minute. It doesn’t take years of training or even months of even days.”