A friend recently told me me that the ghosts that chase Pac-Man in the eponymous arcade game don't vary their behavior based on Pac-Man's position. At first, this surprised me. If, playing Pac-Man, I'm running away from one of the ghosts chasing me, and eat one of the special “energizer” pellets that lets Pac-Man eat the ghosts instead of vice-versa, then the ghost turns and runs away.
My friend responded that the ghosts don't start running away per se when Pac-Man becomes dangerous to them. Instead, they change direction. Pac-Man's own incentives mean that most of the time, while the ghosts are dangerous to Pac-Man, Pac-Man will be running away from them, so that if a ghost is near, it's probably because it's moving towards Pac-Man.
Of course, I had never tried the opposite – eating an energizer pellet near a ghost running away, and seeing whether it changed direction to head towards me. Because it had never occurred to me that the ghosts might not be optimizing at all.
I'd have seen through this immediately if I'd tried to make my beliefs pay rent. If I'd tried to use my belief in the ghosts' intelligence to score more points, I'd have tried to hang out around them until they started chasing me, collect them all, and lead them to an energizer pellet, so that I could eat it and then turn around and eat them. If I'd tried to do this, I'd have noticed very quickly whether the ghosts' movement were affected at all by Pac-Man's position on the map.
(As it happens, the ghosts really do chase Pac-Man – I was right after all, and my friend had been thinking of adversaries in the game Q-Bert – but the point is that I wouldn’t have really known either way.)
This is how to test whether something's intelligent. Try to make use of the hypothesis that it is intelligent, by extracting some advantage from this fact. Continue reading