Whatever casino you are in, slot machines sound more or less the same: jangly music, the whir of spinning reels, accompanied by loud beeps and chimes.
A recent study shows that some of those noises can easily fool our brains into thinking that we won - even when we have unequivocally lost money.
"The way slot machines are designed, sound is a really crucial component of player feedback," said behavioural neuroscientist Michael Dixon of the University of Waterloo in Ontario.
Because the jubilant sounds are always tied to wins or even partial losses - "losses disguised as wins", Dixon, the lead author, calls them - they act as positive reinforcement and can skew our perception of lost money.
Say you wager $1 for a single spin. If you hit a winning combination and win $5, you are rewarded with flashing animations and celebratory jingles made to give you a sense of accomplishment. When you win nothing, the machine goes into a state of rest with no lights or music. It just waits for you to play again.
The catch is, even when you win just a portion of your wager back - for instance, 25 cents out of the dollar you put in - the machine still gives you happy noises and such, similar to when you really win. So even though you have actually lost money, you come away feeling like a winner.
Dixon's team of scientists had 96 gamblers play a slot machine simulator with and without sound and had it programmed to win exactly 28 times out of a total of 200 spins. Afterwards, they asked players how many times they had won out of 200.
For both conditions, players overestimated their number of wins, but by significantly more when the sound was on.
Dixon said these games - particularly multiline slots that allow bets on multiple rows and combinations on a single spin - can be so complex that often people will rely on the machine to tell them whether they have won or lost via sound and lights. So they will listen for those sounds as a cue and think they have won, no matter what the actual outcome.
"I don't think [slots are] a level playing field," Dixon said. He found the manipulation of slot machines disconcerting.
The findings were published online in the Journal of Gambling Studies.
Dixon and computer scientist Kevin Harrigan, of the same university, formed the Gambling Research Lab after Harrigan obtained design documents for slot machines. After analysing the underlying maths and computer algorithms, they realised how deceptive they can be by pushing irrational behaviour and giving players an illusion of control.