Slot is a gambling machine that generates winning combinations by displaying symbols on multiple reels and paying out credits based on the pay table. Most slots have a theme and include traditional icons such as fruits, bells, and stylized lucky sevens. Some have special features such as scatter symbols, free spins, and jackpots. In addition to their visual appeal, slots are often accompanied by high-fidelity attention-grabbing music and amusing animations (Griffiths & Parke 2005; Haas & Edworthy 1996).

Players activate a machine by inserting cash or, in “ticket-in, ticket-out” machines, paper tickets with barcodes that represent credit values. A lever or button, either physical or virtual, then activates the reels. Depending on the machine, the player may have to press the button several times in a row in order to initiate a spin. In most slot machines, winning combinations are formed by matching symbols on a pay line, although some have wild symbols that can substitute for other symbols to complete lines.

While most gamblers enjoy the entertainment value of slot games, a small subset of players can experience severe gambling-related problems that can lead to financial debt, personal relationships, and professional difficulties (Blaszczynski, Sharpe, Walker, Shannon, & Coughlan, 2005). The psychological allure of slots can be attributed to several factors. For example, unlike other forms of gambling, where monetary gains and losses are a constant, feedback from slot machines is immediate. In addition, slot machines offer arousal by using variable ratio reinforcement schedules to randomly elicit wins and losses, making the timing of rewards unpredictable. Moreover, arousal is accentuated by the sound of winning sounds (Rivlin 2004).