Cambridge scientists have developed a ‘Third Thumb’ that could redefine human capabilities

Cambridge researchers have shown that a third thumb, a robotic prosthetic, can be quickly mastered by the public, improving manual dexterity. The study highlights the importance of inclusive design to ensure technology benefits everyone, with significant performance findings across different demographics.

Cambridge researchers have shown that people can quickly learn to control a prosthetic extra thumb, known as a ‘third thumb’, and use it effectively to grasp and manipulate objects.

The team tested the robotic device on a diverse range of participants, which they say is essential to ensure new technologies are inclusive and can work for everyone.

An emerging area of ​​future technology is motor augmentation – using motorized wearables such as exoskeletons or extra robotic body parts to push our motor capabilities beyond current biological limitations.

While such devices could improve the quality of life for healthy individuals who want to increase their productivity, the same technologies can also provide people with disabilities with new ways of interacting with their environment.

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

“These technologies open up exciting new opportunities that can benefit society, but it is important that we consider how they can help all people equally, especially marginalized communities who are often excluded from innovative research and development. To ensure that everyone has the opportunity to participate in and benefit from these exciting advances, we must 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, has developed a third thumb, an extra robotic thumb that aims to increase the wearer’s range of motion, improve their grasping ability, and expand the hand’s carrying capacity. This allows the user to perform tasks that might otherwise be difficult or impossible to complete with one hand, or perform complex multi-handed tasks without the need to coordinate with other people.

Development and functionality of the third thumb

The third thumb is worn on the opposite side of the palm to the biological thumb and is controlled by a pressure sensor located under each big toe or foot. Pressure from the right big toe pulls the thumb across the hand, while pressure from the left big toe pulls the thumb up toward the fingers. The thumb’s range of motion is proportional to the pressure applied, and releasing the pressure will move it back to its original position.

In 2022, the team had the opportunity to test the third finger at the Royal Society’s annual summer science exhibition, where members of the public of all ages could use the device in a variety of tasks. The results are published today in Scientific robotics.

Over five days, the team tested 596 participants ranging in age from three to 96 and from a wide range of demographic backgrounds. Only four of them were unable to use the third thumb, either because it did not fit securely in their hand or because they were unable to control it with their feet (the pressure sensors developed specifically for the exhibition were not suitable for very light children).

Participants were given one minute to familiarize themselves with the device, during which the team explained to them how to perform one of two tasks.

The first task involved picking up pegs from a hanger one by one with only the third thumb and placing them in a basket. Participants were asked to move as many pegs as possible in 60 seconds. 333 participants completed this task.

The second task involved using the third thumb along with the wearer’s biological hand to manipulate and move five or six different foam objects. The objects were of different shapes that required different manipulations, which increased the dexterity of the task. Participants were again asked to move as many objects as possible into the bin within a maximum of 60 seconds. 246 participants completed this task.

Almost everyone could use the device immediately. 98% of participants were able to successfully manipulate objects using the third thumb within the first minute of use, with only 13 participants unable to complete the task.

Performance statistics across demographics

Ability levels varied between participants, but there were no gender differences in performance, nor was performance altered by hand control – despite the thumb always being worn on the right hand. There was no definitive evidence that people who might be considered “good hands”—for example, who learned to play a musical instrument or whose job involved manual dexterity—were better at the tasks.

Older and younger adults had similar levels of ability when using the new technology, although further examination of only the older adults age group revealed a decline in performance with increasing age. The researchers say this effect could be due to a general degradation of sensorimotor and cognitive abilities that are associated with aging and may also reflect a generational relationship to technology.

Performance was generally poorer in younger children. Six of the 13 participants who failed the task were under the age of 10, and of those who did, the youngest children performed worse than the older children. But even older children (aged 12-16) struggled more than young adults.

Dani said: “Augmentation is about designing a new relationship with technology – creating something that goes beyond just a tool and becomes an extension of the body itself. Given the diversity of bodies, it is crucial that the design phase of wearable technology is as inclusive as possible. Equally important is that these devices are available and functional for a wide range of users. In addition, they should be easy for people to learn and quick to use.”

Co-author Lucy Dowdall, also from the MRC Cognition and Brain Science Unit, added: “If motor augmentation – and even wider human-machine interaction – is to be successful, it will need to integrate seamlessly with the user’s motor and cognitive abilities. . We will need to take into account different ages, genders, weights, lifestyles, disabilities – as well as people’s cultural and financial backgrounds, and even how they like or dislike technology. To achieve this goal, physical testing of large and diverse groups of individuals is necessary.”

There are countless examples where a lack of inclusive design considerations has led to technological failure:

• Automatic speech recognition systems that translate spoken language into text have been shown to listen to white voices better than black ones.
• Some augmented reality technologies have been found to be less effective for users with darker skin tones.
• Women face a higher health risk in car crashes because car seats and seat belts are primarily designed to fit “average” male size dummies in crash tests.
• Dangerous power and industrial tools designed for right-handed dominant use or grip have resulted in more accidents when operated by left-handed people who are forced to use their non-dominant hand.

Reference: “Evaluating initial usability of a hand augmentation device in a large and diverse sample” by Dani Clode, Lucy Dowdall, Edmund da Silva, Klara Selén, Dorothy Cowie, Giulia Dominijanni, and Tamar R. Makin, May 29, 2024. Scientific robotics.
DOI: 10.1126/scirobotics.adk5183

This research was funded by the European Research Council, Wellcome, the Medical Research Council and the Engineering and Physical Sciences Research Council.