We further examined the contribution of game luminance fluctuations on pupil diameter. We hypothesized that positively reinforcing slot machine outcomes would be associated with increases in arousal, reflected in larger pupil diameter. Here we investigated pupil dilation derived from eye tracking as a means of capturing changes in sympathetic nervous system arousal following outcomes on a real slot machine. Psychophysiological measures may provide a window into mental processes that underpin these harms. Modern slot machines are among the more harmful forms of gambling. This does not alter our adherence to PLOS ONE policies on sharing data and materials. AJK, WSM, KIM, JF and MS report no conflicts of interest. He has received royalties from Cambridge Cognition Ltd. He has not received any further direct or indirect payments from the gambling industry or groups substantially funded by gambling.

He has received academic consulting fees from Gambling Research Exchange Ontario (Canada), GambleAware (UK), and the International Center for Responsible Gaming (USA). LC has received speaker/travel honoraria from the National Association of Gambling Studies (Australia) and the International Center for Responsible Gaming (USA). LC is the Director of the Centre for Gambling Research at UBC. She has accepted a travel award from the International Multidisciplinary Symposium on Gambling Addiction (Switzerland). She has received a speaker honorarium and travel and accommodation from the Responsible Gaming Association of New Mexico (USA). MVC has received funding from the International Center for Responsible Gaming. MAF has received a speaker honorarium from the British Columbia Lottery Corporation (BCLC). She has not received any further direct or indirect payments from the gambling industry or groups substantially funded by gambling. She has accepted travel or accommodation for speaking engagements from the National Council for Responsible Gambling (USA), the International Multidisciplinary Symposium on Gambling Addiction (Switzerland), and the Responsible Gambling Council (Canada). EHLO has received a speaker honorarium from the Massachusetts Council on Compulsive Gambling (USA). The slot machines used in the present study were provided to the Centre for Gambling Research by the BCLC.

Competing Interests: I have read the journal’s policy and the authors of this manuscript have the following competing interests: The Centre for Gambling Research at UBC receives funding from the Province of British Columbia and the British Columbia Lottery Corporation (BCLC), a Canadian Crown Corporation.

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