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Alliance for Person-Centered Accessible Technologies

an IGERT program developed by ASU & CSULB

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A Natural Sense of Touch

Via Patrick McGurrin

When we think of the design of a prosthetic hand device, one of the most important considerations in question is processing of sensory information. With these devices, our nervous system is unable to process tactile and proprioceptive (i.e. sense of touch from our finger tips/hands and knowing about where our hand is in the space around us, respectively) information. When this information is unavailable, we must carefully watch our movements in order to avoid dropping or damaging an object we grasp. From a practical standpoint, this can make using a prosthetic device burdensome. Thus, we can imagine how using a prosthetic hand can be challenging, as we are constantly distracted and multi-tasking in our everyday lives.

That being said, let’s imagine a prosthetic hand where a user could feel what he or she is grasping. The Swiss Federal Institute of Technology has done just that, and in a recent experiment tested their novel bionic hand. Silvestro Micera and colleagues have successfully created an artificial sense of touch. The big question is: How did they do this? They did so by connecting very small electrodes inside two of the large nerve bundles in the arm. Under normal conditions, nerve bundles gather sensory information, including information about touch, and relay these signals to the brain to let the person know what the hand is feeling. They then connected these electrodes to small sensors in the prosthetic hand. This connection transmitted electrical signals from the prosthetic directly to the nerve bundles when the user grasped an object. Essentially, the device replicated the way in which sensory receptors in the hand transmit information to the brain.

What can the user feel?

Micera and colleagues were able to calibrate their system to the user to allow him to feel how much pressure he was applying, as well as the ability to differentiate different objects based on their size and shape. This is important, for example, when picking up more fragile objects like eggs or a plastic cup. If we squeeze too hard, we will break these things. The user was able to properly identify objects with 90% accuracy.

Potential drawbacks:

Some researchers say that electrodes being inserted into nerve bundles is too invasive, and are currently working on less invasive ways to restore a user’s sense of touch. Dustin Tyler, a researcher at Case Western University, has shown that a less invasive procedure can also restore the sense of touch. However, with this design the sense of touch is also less accurate than that of the design by Micera and colleagues. This brings up an open question about what is best for the user. The tradeoff between how invasive the device needs to be versus how well the device will work to restore a particular function might be best addressed by those in the community who currently use a prosthetic device. Perhaps this feedback could help researchers find a balance in their design that users would find to be the most suitable for their needs.

Availability:

The new bionic hand is not yet available for public use, as further testing is required to ensure that the electrodes are able to continue helping users to feel touch over longer periods of time. Long-term use is the ultimate goal. This would cut down on any problems the user might face after the electrodes have been implanted into the nerves. Nonetheless, the new design is very promising, and is hopeful to have applications toward other sensory modalities.