The flashing lights and jangling bells of casinos slot machines aren’t just a Vegas tradition. They are probably inducing gamblers to gamble even more, a new study suggests.

Researchers led by Catharine Winstanley and Mariya V. Cherkasova from Canada’s University of British Columbia found participants were more likely to make riskier bets in a gambling task where the winnings were paired with audio and visual cues.

“Our data directly demonstrate for the first time that reward-concurrent sensory cues can promote risky choice in human subjects,” they write in a study published in the journal JNeurosci.

The scientists tested two different scenarios measured against the so-called Vancouver Gambling Task, in which participants are asked to choose between a high-reward, low-probability outcome and a lower-reward, higher-probability result.{%recommended 7127%}

Volunteers were shown a pie chart depicting the odds of winning, and then asked to make a selection.

Participants exposed to casino jingles and flashing images of coins when they won “displayed riskier choice and reduced sensitivity to probability information”, the study found.

These “cued” participants also spent less time looking at probability data, and showed pupil dilation, which is tied to arousal.

In another experiment, called the Iowa Gambling Task (IGT), participants chose between four weighted, or rigged, decks of cards. Normal, healthy volunteers will naturally gravitate over time to the decks that more reliably offer rewards. The researchers did not find that adding audio-visual stimuli to the wins in this task affected the outcomes.

“The absence of a clear risk-promoting effect of cues on the IGT may be related to cues accompanying wins, whereas avoidance of risky decks on the IGT is largely driven by loss feedback,” the researchers write. The IGT task did not look at pupil dilation.

Most gambling machines function less like a weighted deck and more like the probability design of the Vancouver test: risk a lot to gain a lot, or risk little to gain little.

The researchers don’t know exactly how the lights and bells work to make people less risk-averse. One theory is that the cues make winning more memorable and thereby distort perception of probability. Another theory is that the cues simply distract the participants from trying to avoid losses.

A previous study found that pairing “bells and whistles” with losses seems to cause participants to interpret losses as wins, the authors note.

“In either case, our findings lend support to the notion that sensory stimulation in gambling could act to de-emphasise the unfavourable odds of winning,” they conclude.