I'd need to go back and look at the code, but it was something primitive but similar to backprop. There was an evaluation routine that compared what lit up on the back of the cube to the desired output. The farther off it was, the more the certainty got docked from any of the [connected] neurons one layer up from the bad pixel, and that dragged down the certainties on the next layer and so on. It didn't have the ability to back check which neurons were involved in which specific output node. But I guess it was a scatter shot attempt at that.