Since their inception in 1893, slot machines have been the most popular form of gambling. Requiring no skill or practice, these machines reward players with money when a combination of symbols appears on the reels. Flashing lights and exciting sounds entice gamblers to play, making slot machines the most profitable component of any casino. In fact, a single machine can generate 67% of all casino profits.

Unlike other forms of gambling, where feedback occurs very slowly or not at all, slot machine results are immediately visible. Further, winning and losing sounds are accompanied by high-fidelity attention-grabbing music and amusing animations, providing a perceptual onslaught that amplifies the arousal of the experience (Loba et al., 2001). The combination of these sensory modalities may explain why slot machines are so popular.

In addition to sound, modern multiline slot machines feature a visual onslaught of animations that highlight the symbols responsible for a particular win. Previous research on auditory feedback has found that congruently paired images and sounds tend to amplify each other (Loba & Bullerjahn, 1994; Bolivar et al., 1994). The use of this effect in slot machines suggests that the arousal of winning is not only caused by a combination of sensory modalities but also by an attention-grabbing reinforcement schedule.

Despite the many technological advances that have taken place over the years, the underlying principles of slot machines remain fundamentally the same. Even today’s newer machines that allow players to choose multiple payout lines and interact with animated characters, which are reminiscent of video game technology, still rely on a Random Number Generator to determine the outcome of each spin.