When I was a kid, I absolutely loved rapidly changing lights patterns, not unlike those in dance clubs or at concerts. When I was six, my grandparents once took me to a concert for kids, with people dressed as characters from fairytales singing and dancing on stage. Well, guess what? I spent more time watching the flashing lights illuminating the stage than I spent watching the show. Afterwards, I could remember all the light colors, but not everything the performers did or sang, let alone any of their names when they introduced themselves after the show.
So if your child is anything like I was, get him a light machine of some sorts. It could be a laser light show projector, a flashing lights device, a cable light that changes colors, or something more tame, like a multicolor lava or glitter lamp. I don't recommend strobe lights, because they can trigger seizures in some people, or black lights, because they emit low doses of ultraviolet light, which can harm the eyes if you look directly at them. (Although if a black light is positioned so that you can't see the bulb, it's fairly safe.) They also have special goggles with little screens in front of the eyes, and the lights shows on them are amazing. But they were outrageously expensive, and I don't know where to find them now; since Sharper Image, who used to sell them, went out of business last year.