Slot machines are more addictive when we see them as having human-like intentions

Slot machines are the great cash cow of the gambling industry, generating the bulk of income in casinos, and today they are also a feature of everyday life, found in high street pubs and bars and online. Slots are exquisitely designed with one purpose in mind, to encourage gamblers to "play to extinction" – that is, until they are penniless – as described at length in Natasha Dow Schüll's Addiction by Design: Machine Gambling in Las Vegas.

Much has been written about the human weaknesses, such as the gambler's fallacy (believing that a win is more likely after a run of losses), that lead people to fall prey to these machines. Now new research published in the Journal of Experimental Psychology: Applied has investigated a hitherto unexplored factor that makes it so tempting for people to just keep playing: "anthropomorphism" – it turns out we squander more on the slots when think of them as intentional adversaries.

The research led by Paulo Riva from the University of Milano-Bicocca asked student participants to play online slot machines for at least one spin, but longer if they wished, supposedly as market research on their design. In one condition participants first read a general description of how the machine is guided by a payout algorithm that produces successes and failures. But crucially, those in the anthropomorphic condition got a different message:

"The slot machine can decide whether you will win or lose a series of bets any time she wants. Sometimes, she may choose to make fun of you, leaving you empty-handed for several bets; other times, she might want to reward you with a win. In any case, the slot machine will always choose what will happen."

Participants in this condition played for significantly longer, often a third or more extra spins (although there was a lot of variability between players within each of the conditions).

Further studies established that even with real incentives not to play – i.e. when any remaining points were converted to sweets or cash prizes – the personified machines still encouraged longer play. One clue as to why this happens is that play with personified machines was associated with stronger positive emotions – fun, excitement and stimulation. Riva's team argue that feeling socially connected to an object (more likely when the object seems human-like) amplifies related emotions, giving a bigger kick to wins and losses. (Note that a larger final study complicated this story: positive strong emotions were again associated with playing for longer, but in this instance the anthropomorphism of slots didn't increase positive strong emotions – this may be due to the different measure of emotion employed, but in any case calls for more research.)

Reflecting on the way slots are typically designed, with icons, characters and fictional tie-ins from Spiderman to Michael Jackson, the researchers suggest that "the gambling industry is selling customers a challenge against a mind rather than just a machine," introducing a competitive and even intimate element to play that helps clear out bank balances.

Before any strong conclusions are drawn, it would be useful to see this paradigm turned from student participants to regular gamblers. Casual gamblers may be drawn into the illusion of competition, but one of the most striking arguments from Schüll's book is that the most compulsive gamblers devote themselves to the slots without expecting or even desiring a fair fight. For these people, playing the slots is a retreat from a life that's hard to control, as the machines give them the opportunity to surrender to a comfortably predictable process: as one interviewee put it, "you accept the certainty of chance: the proof is the zero at the end."

Further reading

Riva, P., Sacchi, S., & Brambilla, M. (2015). Humanizing Machines: Anthropomorphization of Slot Machines Increases Gambling. Journal of Experimental Psychology: Applied DOI: 10.1037/xap0000057