Do you use animals at all in your research?
No - and not just because I am studying human cognition rather than heart or lung function.
What other reason is there? You were editor for 23 years of the journal Behavioral and Brain Sciences (BBS), weren't you? And that journal published human as well as animal studies, didn't it?
Yes. And throughout those 23 years I was deeply troubled, morally, about the animal research BBS published. I had been vegetarian since I turned 17. I tried to minimize animal research in BBS, and only to publish papers that reviewed already published research, rather than reported animal experiments directly in BBS.
But I now realize that there was a lot of self-deception and hypocrisy in my reasoning, and I am deeply ashamed. I am also now vegan, not just vegetarian.
What happened? What changed?
Nothing acute happened. I didn't learn anything I had not known all along. I just reached a threshold in my own rationalizations where I could no longer deny what had been morally obvious, though unspoken, all along: It is wrong to hurt or kill a feeling being if it is not vitally necessary.
That means that there's a conflict of life-or-death interests, as with predator and prey. The Felidae (including lions and tigers as well as house cats) are obligate carnivores; if they do not eat meat, they die. If prey are attacked by predators, they must fight back if they can, otherwise they die. Those are vital interests. In the case of life-saving biomedical research a case can be made for conflict in vital interests: the laboratory animal's life and the human life it could save.