Researchers have found a soft and squidgy water-rich gel is not only able to play the video game Pong, but gets better at it over time.
The findings come almost two years after brain cells in a dish were taught how to play the 1970s classic, a result the researchers involved said showed “something that resembles intelligence”.
The team behind the latest study said that while they were inspired by that work, they were not claiming their hydrogel was sentient.
“We are claiming that it has memory, and through that memory it can improve in performance by gaining experience,” said Dr Vincent Strong, the first author of the research, from the University of Reading.
Strong said the work could offer a simpler way to develop algorithms for neural networks – models that underpin AI systems including Chat GPT – noting that at present they are based on how biological structures work.
Released in 1972, Pong was one of the first video games and has a simple premise: two paddles on a court can be moved up and down to hit a ball back and forth between them. The longer the rally, the higher the score.
Strong’s study focused on a single-player version in which a paddle is moved along one wall of a court to keep a ball bouncing around.
Writing in the journal Cell Reports Physical Science, he and his colleagues describe how they sandwiched an electroactive polymer hydrogel between two plates, each bearing a 3x3 array of electrodes hooked up to a computer system that simulated Pong.
Six of the electrode pairs, in a 3x2 arrangement, were then stimulated to represent the movement of the ball within the game’s court.
Across the other three electrode pairs – representing the wall along which the paddle is located – the team applied a small voltage and the current was measured with sensors. The position of the paddle was defined as the point where the current was highest.
Crucially, the type of hydrogel used in the experiment contains charged ions. These move in response to electrical stimulation and linger where they end up.
As a result, the point along the “wall” with the highest current could shift as the ball moved, meaning the paddle could change position.
“At the beginning the ions are equally and randomly distributed so the paddle hits and misses the ball,” said Strong.
But as the ball bops around the court, the gel receives more and more electrical stimulation.
“Over time the ion concentrations increase where the ball is most, acting as a kind of muscle memory, as with the higher concentrations there are higher electric current readings and the paddle is able to act more accurately,” said Strong.
In other words, the paddle is able to hit the ball more often, resulting in longer rallies.
“Our research shows that even very simple materials can exhibit complex, adaptive behaviours typically associated with living systems or sophisticated AI,” said Dr Yoshikatsu Hayashi, another author of the research at the University of Reading.
Dr Brett Kagan, the chief scientific officer at Cortical Labs, who worked on the Pong-playing brain cells but was not involved in the latest study, said the hydrogel system demonstrates a basic form of memory similar to the way a riverbed records a memory of the river.
That, he said, can be useful to understand how changes within a medium may help electrical signals travel through it better.
But he said significantly more work would be needed to show hydrogels can “learn”.
“The performance and the improvement was tied to a specific location of stimulation. When this was changed in any way the system was not able to reorganise to still show performance,” Kagan said.
“This is different to our tests in neural systems where we showed that regardless of how you presented the information, learning still occurred.”
