The nervous system does an astonishing job of tracking sensory information, and it does so using signals that would drive many computer scientists crazy: a noisy stream of activity spikes that can be passed on to hundreds of additional neurons, where they are integrated with similar spike trains coming from yet other neurons.
Now researchers have used spiking circuits to build an artificial robot skin, adopting some of the principles of how signals from our sensory neurons are sent and integrated. While the system relies on a few decidedly non-neural features, it has the advantage of having chips that can control neural networks using spike signals, which would allow this system to integrate smoothly with low-power hardware to run AI-based control software.
Location via spikes
The nervous system in our skin is remarkably complex. It has specialized sensors for different sensations: heat, cold, pressure, pain and more. In most parts of the body, these end up in the spinal column, where some preparatory processing takes place, allowing reflex responses to be activated without brain involvement. But signals find their way along specialized neurons to the brain, allowing further processing and (potentially) conscious awareness.
The researchers behind the recent work, based in China, decided to implement something similar for an artificial skin that could be used to cover a robot hand. They limited sensing to pressure, but implemented other things the nervous system does, including figuring out the location of inputs and injuries, and using multiple layers of processing.
This all started with creating a flexible polymer skin with built-in pressure sensors connected to the rest of the system via conductive polymers. The next layer of the system converted the input from the pressure sensors into a series of activity spikes: short pulses of electrical current.
There are four ways in which these series of spikes can convey information: the shape of an individual pulse, by their magnitude, by the length of the spike, and by the frequency of the spikes. Spike frequency is the most commonly used means of conveying information in biological systems, and the researchers use that to convey the pressure experienced by a sensor. The remaining forms of information are used to create something similar to a barcode, which can identify which sensor the reading came from.
