Cambridge scientists develop ‘third finger’ that could redefine human capabilities

Researchers in Cambridge have shown that the Third Finger, a robotic prosthesis, can be quickly mastered by the public, increasing manual dexterity. The study highlights the importance of inclusive design to ensure technologies benefit everyone, with important findings on performance across different demographics.

Cambridge researchers demonstrated that people can quickly learn to control the extra prosthetic thumb, known as the “third thumb”, and use it effectively to grasp and handle objects.

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

An emerging area of ​​future technology is motor augmentation – using motorized mobile devices such as exoskeletons or robotic body extensions to advance our motor skills beyond current biological limitations.

While such devices can improve the quality of life for healthy individuals who want to increase their productivity, the same technologies can also offer people with disabilities new ways to interact 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, with machines becoming more and more a part of our daily life, and also our mind and body.

“These technologies open up exciting new opportunities that can benefit society, but it is vital that we consider how they can help all people equally, especially marginalized communities who are often excluded from innovation research and development . To ensure that everyone will have the opportunity to participate in and benefit from these exciting advances, we need to clearly integrate and measure inclusiveness during the earliest possible stages of the research and development process.”

Dani Clode, a collaborator in Professor Makin’s lab, has developed the Third Thumb, an extra robotic finger that aims to increase the user’s range of motion, increase their grasping ability and extend the hand’s carrying capacity. This allows the user to perform tasks that might otherwise be challenging or impossible to perform with one hand or perform complex multi-handed tasks without having to coordinate with other people.

Development and Functionality of the Third Finger

The Third Finger is worn on the opposite side of the palm to the biological thumb and is controlled by a pressure sensor placed under each big toe or foot. Pressure from the right finger pulls the thumb across the hand, while pressure from the left finger pulls the thumb up toward the fingers. The range of motion of the thumb is proportional to the applied pressure, and the release pressure returns it to its original position.

In 2022, the team had the opportunity to test the Third Thumb at the Royal Society’s annual Summer Science Exhibition, where members of the public of all ages were able to use the device during various tasks. The results were published today 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. Of these, only four were unable to use the third finger, either because it did not fit well with 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 up to one minute to familiarize themselves with the device, during which time the team explained how to perform one of two tasks.

The first task involved picking up pegs from a board one at a time with the third finger and placing them in a basket. Participants were asked to move as many pins as possible in 60 seconds. 333 participants completed this task.

The second task involves 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 to use, increasing the dexterity of the task. Again, participants were asked to move as many objects as they could into the bin within a maximum of 60 seconds. 246 participants completed this task.

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

Performance insights across demographics

The skill levels among the participants varied, but there were no differences in performance between the sexes, nor did hand length change performance—despite the fact that the thumb was always held on the right hand. There was no conclusive evidence that people who could be considered ‘good with their hands’ – for example, they were learning to play a musical instrument, or their work involved manual dexterity – were better at tasks.

Older and younger adults had a similar level of skill when using the new technology, although further investigation only within the age group of older adults revealed a decline in performance with increasing age. The researchers say this effect may be due to the general degradation in sensorimotor and cognitive abilities associated with aging and may also reflect a generational relationship with 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 completed the task, younger children tended to perform worse than 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 extends beyond just being a tool to become an extension of the body itself. Given the diversity of bodies, it is essential that the design phase of the clothing technology be as inclusive as possible. It is equally important that these devices are accessible and functional for a wide range of users. Furthermore, 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 wider human-machine interactions – are to be successful, they will need to be seamlessly integrated with motor skills and user recognition. . We’ll have to take into account people’s ages, genders, weight, lifestyles, disabilities – as well as people’s cultural, financial backgrounds, and even technology likes or dislikes. Physical testing of large and diverse groups of individuals is essential to achieve this goal.”

There are countless examples where the lack of comprehensive design considerations has led to technological failure:

• Automated speech recognition systems that convert spoken language to text have been shown to perform better listening to white voices compared to black voices.
• Some augmented reality technologies have been found to be less effective for users with darker skin tones.
• Women face a higher health risk from car accidents, due to car seats and seat belts being designed primarily to accommodate ‘average’ sized male dummies during crash testing.
• Hazardous power and industrial tools designed for right-hand dominant use or grip have resulted in more accidents when used by left-handers forced to use their non-dominant hand.

Reference: “Evaluating the 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.