The effects of reward uncertainty and alcohol intoxication on human sign- and goal-tracking.

rationalSign- and goal-tracking (ST/GT) behaviors capture individual differences in reactivity to reward-predictive cues and are increasingly recognized as translational markers of addiction vulnerability. While animal research shows that cue-reward uncertainty (i.e. the inability to predict whether a reward will follow its predictive cue) and alcohol modulate sign-tracking, empirical evidence in humans remains scarce. This experimental study investigated how acute alcohol intoxication and cue-reward uncertainty shape attentional responses to reward cues in humans.

methodsOne hundred eighteen young adult participants were assigned to one of four groups in a 2 × 2 design: Alcohol (0.5 g/kg) vs. Placebo and Uncertain (50% reinforcement) vs. Certain (100% reinforcement) reward conditions. Eye-tracking during a Pavlovian conditioned approach (PCA) task quantified ST/GT tendency, followed by a non-rewarded “omission” phase.

resultsReward uncertainty significantly increased attentional allocation to the reward-predictive cue (η²p = 0.04), consistent with animal evidence that uncertain outcomes amplify responses to conditioned cues. Contrary to predictions, alcohol did not produce reliable enhancements of sign-tracking (η²p = 0.01). Effects during reward omission were mixed: the groups that previously experienced reward certainty increased their attention towards the sign while decreasing their attention towards the goal. Exploratory analyses incorporating initial ST/GT tendencies as covariates further indicated that cue-attention during omission aligned with participants’ initial ST/GT behavior.

conclusionsReward uncertainty, but not alcohol intoxication, affected sign-tracking tendencies. By directly translating animal findings to a human paradigm with eye-tracking, these results support the idea that uncertainty affects how individuals orient toward reward-predictive stimuli, a process relevant to theories of addictive behavior.