Final answer:
To study choice and preference, a concurrent schedule of reinforcement should be used. Slot machines use a variable-ratio schedule, which is the most effective partial reinforcement schedule for maintaining high and consistent levels of engagement.
Step-by-step explanation:
To investigate choice and preference, it is important that the organism be presented with a concurrent schedule of reinforcement. This allows researchers to examine which of two or more reinforcements is more effective by presenting them simultaneously to the subject, who can then choose between them.
As for slot machines, they reward gamblers with money according to a variable-ratio reinforcement schedule. In this type of schedule, the number of responses needed for a reward varies and this unpredictability contributes to the high level of engagement slot machines engender in gamblers. It is considered the most powerful partial reinforcement schedule due to its high resistance to extinction and steady, high response rates.