Third Thumb: People Have No Trouble Mastering an Extra Thumb, Study Finds

Cambridge researchers have shown that members of the public have no difficulty learning very quickly to use a third thumb – a controllable prosthetic extra thumb – to grasp and manipulate 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. The results are published in Scientific robotics.

An emerging area of ​​future technology is motor augmentation, which uses powered wearable devices such as exoskeletons or extra-robotic body parts to advance our motor abilities beyond current biological limits.

While such devices could improve the quality of life for healthy people who want to increase their productivity, these same technologies can also offer people with disabilities new ways to interact with their environments.

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 doing more more part of our daily lives, and even our minds and bodies.

“These technologies open up exciting new opportunities that can benefit society, but it is essential that we think about how they can help everyone equally, particularly marginalized communities who are often excluded from research and development. development in terms of innovation.

“To ensure that everyone will have the opportunity to participate and benefit from these exciting advances, we must explicitly embed and measure inclusiveness at the earliest possible stages of the research and development process.”

Dani Clode, a collaborator in Professor Makin’s laboratory, developed the Third Thumb, an additional robotic thumb aimed at increasing the user’s range of motion, improving their gripping ability, and increasing the load-bearing capacity of the hand. This allows the user to perform tasks that might otherwise be difficult or impossible to complete with one hand or to perform complex tasks with multiple hands without having to coordinate with other people.

The third thumb is worn on the opposite side of the palm to the biological thumb and controlled by a pressure sensor placed under each big toe or foot. Pressure from the right toe pulls the thumb onto the hand, while pressure from the left toe pulls the thumb toward the fingers. The amount of movement of the thumb is proportional to the pressure applied, and releasing the 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 different tasks.

Over the course of 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 their hand well or because they could not control it with their feet (the pressure sensors developed specifically for the exhibition were not suitable for very light children). ).

Participants had one minute to familiarize themselves with the device, during which time the team demonstrated how to perform one of two tasks.

The first task was to pick up pegboard pegs one by one with only the third inch and place them in a basket. Participants had 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 with the wearer’s biological hand to manipulate and move five or six different foam objects. The objects were of various shapes which required different manipulations, thus increasing the dexterity of the task. Again, participants were asked to move as many objects as possible into the basket in no more than 60 seconds. A total of 246 participants completed this task.

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

Ability levels between participants varied, but there were no gender differences in performance, nor did handing change performance, although the thumb was always 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 job involved manual dexterity) were better at these tasks.

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

Performance was generally lower in younger children. Six of the 13 participants who could not complete the task were younger than 10 years old, and among those who completed the task, younger children tended to perform worse than older children. But even older children (ages 12 to 16) had more difficulty than young adults.

Dani said: “Augmentation is about designing a new relationship with technology, about creating something that goes beyond just the tool to become an extension of the body itself. Given the diversity of bodies, it is crucial that the design stage 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. Additionally, they should be easy to learn and use quickly.

Co-author Lucy Dowdall, also from the MRC’s Cognition and Brain Science Unit, added: “If motor augmentation, and even broader human-machine interactions, are to succeed, they will need to integrate with transparently to the motor and cognitive abilities of the user. To achieve this, we will need to take into account different ages, genders, weights, lifestyles, disabilities, as well as people’s cultural and financial backgrounds, and even their likes or dislikes for technology. aim.”

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

• Automated speech recognition systems that convert spoken language into text have been shown to result in better hearing of white voices compared to black voices.
• Some augmented reality technologies have been shown to be less effective for users with darker skin.
• Women face a higher health risk in car crashes because car seats and seat belts are primarily designed to accommodate “average” male-sized dummies in crash tests.
• Dangerous power and industrial tools designed for right-handed use or dominant grip have led to more accidents when used by left-handed people forced to use their non-dominant hand.