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Cambridge researchers have shown that people have little trouble learning very quickly how to use a third thumb – a controllable, prosthetic extra thumb – to pick up and manipulate objects.

The team is testing the robotic device on a diverse set of participants, which they say is essential to ensure that new technologies are inclusive and can work for everyone. The results are published in Scientific robotics.

An emerging area of ​​future technology is motor augmentation—the use of motorized wearables such as exoskeletons or additional robotic body parts to advance our motor abilities beyond current biological limitations.

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

Professor Tamar Makin, from the Medical Research Council (MRC) Cognitive 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 increasingly becoming part of our everyday lives and even our minds and bodies.

“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 research and innovation development.”

“To ensure that everyone has the opportunity to participate and benefit from these exciting advances, we must explicitly integrate and measure inclusion during the earliest possible stages of the research and development process.”

Danny Claude, an associate in Professor Makin’s lab, developed the Third Thumb, an additional robotic thumb aimed at increasing the wearer’s range of motion, improving their grasping ability and expanding the hand’s carrying capacity. This allows the user to perform tasks that would otherwise be challenging or impossible to perform with one hand, or to perform complex multi-handed tasks without having to coordinate their actions with other people.

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

In 2022, the team had the opportunity to test Third Thumb at the Royal Society’s annual summer science exhibition, where members of the public of all ages could use the device during a variety of tasks.

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 Thumb either because it did not fit tightly on their hand or because they could not control it with their feet (the pressure sensors developed specifically for the exhibition are 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 complete one of two tasks.

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

The second task involved using the third thumb along with the user’s biological hand to manipulate and move five or six different foam objects. The objects were of different shapes that required different manipulations to increase 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. A total of 246 participants completed this task.

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

Ability levels varied between participants, but there were no gender differences in performance, nor did handedness alter performance—although the thumb was always worn on the right hand. There was no definitive proof that people who might be considered “good with their hands” — for example, they learned to play a musical instrument or their jobs involved manual dexterity — were better at the tasks.

Older and younger adults had a similar level of ability in using the new technology, although further examination within the older age group alone revealed a decline in performance with increasing age. The researchers say this effect may be due to the general deterioration of sensorimotor and cognitive abilities that are associated with aging, and may also reflect the relationship between generations and technology.

Performance is generally worse among 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 (ages 12-16) struggle more than young adults.

Danny said: “Augmentation is about designing a new relationship with technology – creating something that extends beyond a mere tool and becomes an extension of the body itself. Given the diversity of bodies, it is critical that the design stage of wearable technology is as inclusive as it is equally important that these devices are accessible and functional for a wide range of users, and they must be easy to learn and use quickly.’

Co-author Lucy Dowle, also from the MRC’s Department of Cognitive and Brain Sciences, added: “If motor augmentation – and even wider human-machine interactions – are to be successful, they will need to integrate seamlessly with motor and cognitive user capabilities We will need to take into account people’s different ages, genders, weights, lifestyles, disabilities as well as cultural, financial backgrounds and even their likes and dislikes of technology is essential to achieving this goal. “

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

• Automated speech recognition systems that convert spoken language into text have been shown to perform better at 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 crashes because car seats and seat belts are primarily designed to fit “average” male-sized dummies during crash tests.
• Dangerous power and industrial tools designed to be used or gripped with the dominant right hand have resulted in more accidents when operated by left-handed people forced to use their non-dominant hand.