Slot machines use a bunch of interesting psychological techniques. They are set up to produce "near misses", where the reels show you almost win, with the winning symbol just below the pay line. They create losses that appear as wins - you win less than you put in, so it feels like a win even though you lost money. They use a mapping so the odds of a reel stopping on something good are less than its physical fraction of the reel. They produce an illusion of control, since pushing the stop button has no effect on the result.
The worst part is that no matter how much you know that this is the case, it can be exceptionally hard not to be taken in by that "man, I was thiiiis close" feeling. I'd throw the famous Wargames quote in here, and not playing is, for me, definitely the only time I "win", but instead I'll quote everyone's favorite philosophical physicists:
"So I started betting, and right away I lost five dollars in succession — one, two, three, four, five. I was supposed to be out only seven cents; instead, I was five dollars behind! I've never gambled since then (with my own money, that is). I'm very lucky that I started off losing."
Back to the idea of near misses, I spent an afternoon reading webpages like this one...
...which show with charts how the "near miss" effect works. I then went ahead and blew the $20 that was in my pocket the next time I was in a casino for a buffet dinner. I play games that I enjoy, with the licenses, all the lights and sounds and big numbers and terrible payouts. I have some fun losing, but never as much fun as I'd have with 1/4th the money if I just took it down the street to the Pinball Hall of Fame arcade.
A virtual reel can have thousands of stops. 99% of those can map to the same physical space. That's the magic of Telnaes.
A typical PAR sheet is mentioned in the study two leaps above, but that's just reverse-engineering the math. Understanding virtual reels helps look at it from the designer's direction.
The invention of "bonus games" that play when a certain reel combination was hit also changed the math drastically. A lot of companies that were locked out of virtual reels by IGT's ownership of the Telnaes patent used this technique to offer similar payout structures.
That's probably true I'm just going by memory and what we have.
IGT seems to own all, it's like you can't touch a thing without IGT being involved. I've even heard stories of potential new IGT employees being asked if they have any invention ideas, if they do IGT will but them.
This all comes from a research paper: http://www.nh.gov/gsc/calendar/documents/20091117_harrigan_d...