A slot, or groove, is a narrow notch, depression or opening, as in a keyway in machinery or a slit for a coin in a vending machine. Webster’s New World College Dictionary, 4th Edition 2010 by Houghton Mifflin Harcourt. All rights reserved.

When it comes to casino gambling, few things are more carefully engineered than the slot machines. They have an almost mystical hold over people, and they’re responsible for a large portion of the industry’s profits. Yet despite their dominance, they aren’t very well understood. This article explores some of the mysteries behind the magic that makes a slot work and how casinos use it to lure people in and keep them playing.

In the old days, when you yanked a lever on a slot machine, it was all or nothing: All the cherries or lucky 7s lined up and you won; they didn’t and you lost. But with the advent of computerized slots, gamblers can now wager on up to 200 lines at a time on the video screen — up, down, diagonal, or sideways — and each has a chance of winning.

This is supposed to make the machines more exciting and increase a gambler’s persistence. But experimental results have been mixed. A notable concern is that conventional chained procedures that successfully produce conditional reinforcement require a contingency between the putative conditional reinforcer and subsequent unconditional reinforcer, which is not present in a classic slot machine.