When Dr. Caligin was in charge, yes. But at some point near the end of his experiments, he let everyone go. Paid them, sent them home, cut all ties from them in order to keep them safe from the repercussions of his research.

[He sits forward in his seat.] You were and you weren't. When you and the other original otherworlders were sent home, you were merely being observed, but when he felt it was time to bring you back, he did. The second time you were sent home--when I sent you home [Nathan sounds a bit angry now]--the experiment continued. Had I realized what was going on, I wouldn't have tried to send you home. It wasn't fair to any of you.

As for what he's looking for... [His expression darkens] Only he truly knows. It's different for everyone. I've seen him bring people here, perfectly kind and wonderful people, and ones who were quite interesting, and he'd reject them all. Maybe he'd give them a trial run, see how they do here, but for whatever reason, he's sent them home.

And it makes all the difference that you're not of this universe. His experiments wouldn't work if he tried it with people from our own.