In Slot, cultural anthropologist Rachel Schull takes us into casinos where she discovers that almost everything from the patterns on the carpet to the position of the armrests is explicitly engineered to make gambling more seductive and get people spending more money. She also shows how casinos have drawn on psychological insights to make their slot machines and video games even more addictive.

The earliest slot machines were simple: you pulled the lever and either won or lost. But today’s multi-line slot machines display dozens of possible lines on the screen up, down, diagonally, and every combination in between. When the symbols line up in a winning combination, the player wins credits based on how much they bet before.

But why do some people keep playing, even when they know that the odds of hitting a jackpot are one in a million? In her interviews, Schull found that for many of the people she spoke to, slots have become less about the chance of a big win and more about the gradual drip feed of small wins.

Schull and her colleagues conducted an experiment to test whether near-miss feedback might increase gambling persistence. In the first phase of the study, participants played three concurrently available slot machines that each had a different frequency of near-miss presentations (e.g., 15%, 30%, and 45%). The results of this experiment support the notion that near-miss feedback increases gambling persistence, although the exact mechanism is unclear. One possibility is that the audio-visual stimuli correlated with near misses on slot machines acquire conditionally reinforcing properties, just like the feedback associated with free throws in basketball.