D Levy did experiments back in the 1930s and 40s predominately. The study too small to tell if valid. Furthermore, I'd be curious what type of "punishment" they used to correct the dogs over food. Somehow, I am not surprised that the softer dogs indulged and then punished came to not trust humans. Children with the push/pull (love/abuse) type parents also fare worse in some research stats than those with cold/abuse.
I cannot locate the original article, but I did find there are several. I am not sure what agnostic means in this context lol: (this actually was 1968):
http://onlinelibrary.wiley.com/doi/10.1002/dev.420010211/abstract