A couple of years ago, I set out to do an experiment very similar to this one.
The scientists then put the robots in a little arena with two glowing red disks. One disk they called the food source. The other was the poison source. The only difference between them was that food source sat on top of a gray piece of paper, and the poison source sat on top of black paper. A robot could tell the difference between the two only once it was close enough to a source to use its infrared sensor to see the paper color.
Then the scientists allowed the robots to evolve. The robots–a thousand of them in each trial of the experiment–started out with neural networks that were wired at random. They were placed in groups of ten in arenas with poison and food, and they all wandered in a haze. If a robot happened to reach the food and detected the gray paper, the scientists awarded it a point. If it ended up by the poison source, it lost a point. The scientists observed each robot over the course of ten minutes and added up all their points during that time.
Never finished it, sadly. One day I will.
Be sure to watch the cool video of the cooperating robots.