Issues: Research is mainly on non-human animals

This may not be applicable to humans as we are different from animals- we have conscious insight for example- so we may not entirely learn through stimulus response relationships.
It could also be seen as unethical: Pavlov did surgery on his dogs which was irreversible solely for his research then had them put down after, Skinner electrocuted rats.
However, it is supposedly more ethical to test on animals than humans, and this testing has led to important discoveries.