Very interesting. I have trained my dogs to recognize the names of a few different toys (when I say the name of a toy, they can retrieve it from a group of toys and drop it in a basket). I was, however, unable to train them to recognize photos of those same toys taken on plain backgrounds. My inability to train them doesn't mean they can't learn to do it, but it did make me wonder if such a seemingly simple perceptual task might be significantly different for them. Your article suggests that dog and human perception may indeed be very different.