Scientists have used laser light to activate neurons in a mouse's brain so the rodents "sees" non-existent lines. The technique, called optogenetics, switches on and off neurons that have been previously genetically engineered to be light-sensitive. According to Science News, "the results, described online July 18 in Science, represent the first time scientists have created a specific visual perception with laboratory trickery." In this case, the mice had been trained to drink water from a spout upon seeing the lines.