Just look at the one figure in the paper and you will see. Because your final layer is positively encoded, that polarity trickles down through back propogation

Just look at the one figure in the paper and you will see. Because your final layer is positively encoded, that polarity trickles down through back propogation. I also think the positive weights thing is to do with the way features normally work. It makes sense to look for corners, not anti corners for object detection.