A narrow opening for receiving or admitting something, as a coin or letter. Also: a place or position with a particular function, especially in a group of morphemes or a construction; compare filler (def 9). A slot in the roof of a ship or a building. A time slot on a broadcasting schedule. A specific position or job, such as the one held by the chief copy editor of a newspaper.

Slots are a unique form of gambling machine that gets into gamblers’ heads as well as their wallets. Their design combines engineering acumen, mathematical know-how and psychological deceit in a neatly packaged package that appeals to our intuitive understanding of probability.

The reason for the popularity of slots lies in their ability to create both arousal and positive affect in their players. Arousal is generated by the fact that monetary gains are accompanied by high-fidelity attention-grabbing music and amusing animations. This arousal is further enhanced by the fact that it is never known when wins will occur, because winning and losing are randomly offered to players using a variable-ratio reinforcement schedule. This study adds to the literature by assessing whether sounds contribute to this arousing effect and by measuring the extent to which dark flow accounts for enjoyment of slots that differ from enjoyment attributable to reward reactivity. In contrast to other psychophysiological measures that require cumbersome electrodes and wires that likely reduce ecological validity, these two new measures are derived from data collected during participants’ natural playing sessions on a real slot machine.