Cambridge scientists develop ‘third thumb’ that could redefine human ability

Researchers in Cambridge have shown that the Third Thumb, a robotic prosthetic device, can be quickly mastered by members of the public, improving dexterity. The study highlights the importance of inclusive design to ensure technologies benefit everyone, with key findings on performance across different demographics.

Researchers from Cambridge have shown that people can quickly learn to control an extra prosthetic thumb, also known as a ‘third thumb’, and use it effectively to grasp and handle objects.

The team tested the robotic device on a wide 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 wearable devices such as exoskeletons or additional robotic body parts to advance our motor capabilities beyond current biological limitations.

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

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

“These technologies offer exciting new possibilities that society can benefit from, but it is critical that we consider how they can benefit all people equally, especially marginalized communities who are often excluded from innovation research and development . To ensure that everyone has the opportunity to participate and benefit from these exciting advances, we must explicitly integrate and measure inclusivity at the earliest possible stages of the research and development process.”

Dani Clode, an employee of Professor Makin’s laboratory, has developed the Third Thumb, an additional robotic thumb intended to increase the wearer’s range of motion, increase their gripping ability and increase the hand’s load-bearing capacity. This allows the user to perform tasks that are otherwise challenging or impossible to perform with one hand, or to perform complex multi-handed tasks without having to coordinate with other people.

Development and functionality of the third thumb

The third thumb is worn on the opposite side of the palm from the biological thumb and is controlled by a pressure sensor placed under each big toe or foot. Pressure from the right toe pulls the thumb over the hand, while the pressure exerted with the left toe pulls the thumb up toward the fingers. The magnitude of the thumb’s movement is proportional to the pressure applied, and releasing the pressure returns the thumb to its original position.

In 2022, the team had the opportunity to test the Third Thumb at the annual Royal Society Summer Science Exhibition, where members of the public of all ages could use the device during a variety of tasks. The results are published today in Science Robotics.

Over five days, the team tested 596 participants, ranging in age from three to 96 years old and from a wide range of demographic backgrounds. Of these, only four could not use the Third Thumb, either because it did not fit properly in their hand or because they could not operate it with their feet (the pressure sensors specially developed 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 the two tasks.

The first task consisted of picking up pegs one by one from a pegboard using only the Third Thumb 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 involved using the Third Thumb together with the wearer’s biological hand to manipulate and move five or six different foam objects. The objects had different shapes that required different manipulations, increasing the dexterity of the task. Again, participants were asked to move as many objects as possible into the basket 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 during the first minute of use, with only 13 participants unable to perform the task.

Performance insights across demographics

Skill levels varied between participants, but there were no differences in performance between genders, and dexterity did not change performance either – despite the thumb always being worn on the right hand. There was no definitive evidence that people who could be considered ‘good with their hands’ – for example, they learned to play a musical instrument or their work involved manual dexterity – were better at these tasks.

Older and younger adults had similar skill levels in using the new technology, although further research within the age range of older adults revealed a decline in performance with advancing age. The researchers say this effect could be due to the general decline in sensorimotor and cognitive skills associated with aging and may also reflect a generational relationship with technology.

Performance was generally poorer among younger children. Six of the thirteen participants who were unable to complete the task were under ten years old, and of those who did complete the task, the youngest children tended to perform worse than older children. But even older children (ages 12 to 16) had more difficulty with it than young adults.

Dani said: “Augmentation is about designing a new relationship with technology – creating something that goes beyond just a tool, but 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. It is equally important that these devices are accessible and functional for a wide range of users. Moreover, they must 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 interactions – are to be successful, they will need to integrate seamlessly with the motor and cognitive skills of the user. . We will have to take into account different ages, genders, weight, lifestyles, disabilities – as well as people’s cultural and financial backgrounds, and even technology likes or dislikes. Physical testing of large and diverse groups of individuals is essential to achieving this goal.”

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

• Automated speech recognition systems that convert spoken language to text have been shown to perform better when listening to white voices than black voices.
• Some augmented reality technologies appear to be less effective for dark-skinned users.
• Women face a greater health risk from car accidents because car seats and seat belts are primarily designed for “average” male dolls in crash tests.
• Dangerous power and industrial tools designed for dominant right-handed use or grip have led to increased accidents when operated by left-handers who are forced to use their non-dominant hand.

Reference: “Evaluation of the Initial Usability of a Handheld Magnification Device on 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, Science Robotics.
DOI: 10.1126/scirobotics.adk5183

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