In the early days of television sitcoms, they were filmed in front of a studio audience. It forced the actors to perform better and offered a real soundtrack to the show you were watching because you could listen to the audience roaring in laughter in the background.
More importantly, the laughing was a cue to the audience watching at home that something funny was happening. At one point a clever sound engineer figured out that they could get the same effect by using simulated laughter in place of a live audience, and the laugh track was born.
The thing about laughter is that it is contagious -- when you hear others laughing, simulated or not, you can't help but laugh. This is not limited to sitcoms or to laughter. There are many behaviors that you may want your customers to take which are similarly contagious. The Laugh Track Principle is about illustrating desirable behaviors so you can illicit those same behaviors from a wider group of people.
Here a few examples of businesses that are using the "laugh track principle" to succeed:
1. Gilt Groupe with "Sold Out" and "In Member's Carts" - Login to this invitation only daily deals website and you'll notice that many of the products are either sold out or have a banner across their image sharing that the product is otherwise unavailable because someone else found it first. This, along with their focus on encouraging fast conversion by limiting how long a product can stay in your shopping cart, means that they are creating a perception that no product on the site will be around for long, so you better decide fast and buy it.
2. Las Vegas Casinos. There are few psychological tricks that the Casinos wouldn't have looked at and the laugh track principle is no exception. On the floors with slot machines there are beeping and ringing machines that set off sirens and music when someone wins any sort of jackpot. The sound and light show gives other gamblers the sense that they might be close to winning too -- and keeps them firmly in their seats.
3. Restaurant windows or terraces. This is the simple technique that many restaurants use of seating people either in the window or outside on a terrace or some other visible location to give the impression to passersby that the restaurant is popular and worth dining at.
4. Telethon-style thermometer bulbs. The thermometer bulb model for tracking donations may seem tired and old, but remains a highly effective way of demonstrating to people the impact that their individual contributions can have as part of a collective effort. The everyday example of that is a tip jar with some change to start it off, but waiting for more contributions.