Do pupillary responses during authentic slot machine use reflect arousal or screen luminance fluctuations? A proof-of-concept study

Abstract

Modern slot machines are among the more harmful forms of gambling. Psychophysiological measures may provide a window into mental processes that underpin these harms. 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. We hypothesized that positively reinforcing slot machine outcomes would be associated with increases in arousal, reflected in larger pupil diameter. We further examined the contribution of game luminance fluctuations on pupil diameter. In Experiment 1A, experienced slot machine gamblers (N = 53) played a commercially-available slot machine in a laboratory for 20 minutes while wearing mobile eye tracking glasses. Analyses differentiated loss outcomes, wins, losses-disguised-as-wins, and (free-spin) bonus features. Bonus features were associated with rapid increases in pupil diameter following the onset of outcome-related audiovisual feedback, relative to losses. In Experiment 1B, luminance data were extracted from captured screen videos (derived from Experiment 1A) to characterize on-screen luminance changes that could modulate pupil diameter. Bonus features and wins were associated with pronounced and complex fluctuations in screen luminance (≈50 L and ≈25L, respectively). However, the pupil dilation that was observed to bonus features in Experiment 1A coincided temporally with only negligible changes in screen luminance, providing partial evidence that the pupil dilation to bonus features may be due to arousal. In Experiment 2, 12 participants viewed pairs of stimuli (scrambled slot machine images) at luminance difference thresholds of ≈25L, ≈50L, and ≈100L. Scrambled images presented at luminance differences of ≈25L and greater were sufficient to cause pupillary responses. Overall, pupillometry may detect event-related changes in sympathetic nervous system arousal following gambling outcomes, but researchers must pay careful attention to substantial in-game luminance changes that may confound arousal-based interpretations.

Electronic gambling machines and dopamine.

“…A similar disconnect has been emphasized with respect to the neural reactivity to addiction-related stimuli (cue-reactivity), where effects tend to be more pronounced for cues with higher ecological validity [109][110][111]. Psychophysiological and eye-tracking approaches, on the other hand, study gambling on actual [112][113][114] or simulated EGMs [94,105], but face challenges with respect to confounding effects (e.g. luminance effects on pupillometry [112]).…”

“…Psychophysiological and eye-tracking approaches, on the other hand, study gambling on actual [112][113][114] or simulated EGMs [94,105], but face challenges with respect to confounding effects (e.g. luminance effects on pupillometry [112]). Psychophysiological approaches likewise struggle with the fast-paced timing of EGMs.…”

Engineered highs: reward variability and frequency as potential prerequisites for behavioural addiction

“…In modern slot machines, the variable ratio governs delivery of monetary wins, but most games also offer rarer 'bonus features', which can be a number of free spins, or a separate 'game within a game' (Parke & Griffiths, 2006). Regular slot machine gamblers highly value these bonus features when choosing which game to play (Landon et al, 2018), and receipt of bonus features is physiologically arousing (Kim et al, 2022;Moodie & Finnigan, 2005). Third, the bonus features are signalled by special symbols that are often over-sized and accompanied by a unique auditory signature, and in this way, bonus features also enable 'near-miss' outcomes: when 2 out of 3 required bonus symbols are displayed, it is highly salient to the gambler that they just missed the bonus round, even on a visually-complex 'multi-line' game (Dixon et al, 2015).…”