In parallel, electroencephalography (EEG) activity was recorded in the relevant somatosensory regions of the amputee's brain to confirm phantom hand activation during stimulation.
Rich with all this experimental data, the researchers then developed a neuromorphic representation of the tactile signal, with the aim to transform the e-dermis (electronic skin) signal from a pressure signal into a biologically relevant signal, namely, a spiking response similar to what actual mechanoreceptors and nociceptors would provide.
Fed into a transcutaneous electrical nerve stimulator, the neuromorphic signal transduction conveyed the changes in the tactile signal as changes in stimulation frequency and pulse width, matching the perceived levels of touch or pain recorded during all the previous sensory feedback experiments.
Ultimately, this neuromorphic signal transduction allowed the prosthesis wearer to differentiate between safe (innocuous) and painful (noxious) tactile sensations when grasping rounded or spiky objects between an e-dermis-covered thumb and index finger.
Pain is of no use if you don't react to it. Hence to enforce prosthesis self-preservation, the scientists also modelled as a polysynaptic withdrawal reflex that would prevent damage and further pain. They note that although they implemented an autonomous pain reflex, such reflex component could be modulated by the user based on the perceived pain or even, for example using the amputee’s electromyography (EMG) signal as an additional input to the reflex model.
In the future, the researchers envisage an e-dermis with multiple types of sensors for a richer feedback (including the detection of temperature and possibly noxious chemicals). Such an electronic tactile skin could find applications in robotics too as a natural safeguard for sharp objects handling robots.
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