This large-scale study was a collaborative and interdisciplinary effort, bridging cognitive neuroscience and robotics. We’d like to thank all the researchers and participants who made this work possible. Thanks for reading! 🙏 Check out the full preprint here: www.biorxiv.org/content/10.1...
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However, participants preferred using their hand over the Thumb in more naturalistic tasks where the Thumb’s use was optional. This suggests that factors beyond skill transfer, cognitive effort, and embodiment must be addressed for real-world adoption of these promising technologies.
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We also found that training improved participants’ sense of agency over the device. The greater their motor gains after training, the stronger their sense of agency over the Thumb.
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Next, we tested whether flexible control of the Thumb depends on high-level cognitive resources. We found that although participants performed a bit worse with the Thumb while doing a math calculation task, training reduced the effort needed to use the device.
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We then switched the Thumb’s controller (toes) and the body part it was worn on (right hand) to different body parts. Participants still showed complete skill transfer, suggesting Third Thumb skill isn’t limited by specific sensorimotor body mappings.
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To assess if motor learning was task-specific, we tested participants on untrained tasks. Even when postural demands increased—balancing on a board while controlling the Thumb with their toes!—they showed significant gains, suggesting motor skill transfer across tasks and body postures.
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We trained participants intensively with the Thumb for seven days on tasks promoting motor exploration. Despite most training happening at home with minimal supervision, participants showed highly significant improvements in every practiced task.
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In this study, we tested whether humans could flexibly control an extra robotic thumb, the Third Thumb, worn on the right hand and controlled via the toes, beyond the specific tasks and conditions in which they trained.
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Imagine having to relearn how to scroll or type with every new app 🤯. Our ability to transfer motor skills across tools makes modern technology usable. But can skill transfer with novel and complex technologies, like extra robotic limbs, be just as flexible?
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Can humans use artificial limbs for body augmentation as flexibly as their own hands?
🚨 Our new interdisciplinary study put this question to the test with the Third Thumb (@daniclode.bsky.social), a robotic extra digit you control with your toes!
www.biorxiv.org/content/10.1...
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Excited to share our new interdisciplinary work exploring the sensory representation of an artificial body part, combing datasets and methodologies to explore sensorimotor integration of the Third Thumb, a 2 DoF hand augmentation device (@daniclode.bsky.social) doi.org/10.1101/2025.06.16.658246