Winkielman, P., Berridge, K. C., & Wilbarger, J. (2005). Unconscious affective reactions to masked happy versus angry faces influence consumption behavior and judgments of value. Personality and Social Psychology Bulletin, 1, 121-135.

We explored three properties of basic, unconsciously-triggered affective reactions. First, they can influence consequential behavior. Second, they work without eliciting conscious feelings. Third, they interact with motivation. We investigated these properties by testing the influence of subliminally presented happy versus angry faces on pouring and consumption of beverage (Study 1), perception of beverage value (Study 2), and reports of conscious feelings (both studies). Consistent with incentive motivation theory, the impact of affective primes on beverage value and consumption was strongest for thirsty participants. Subliminal smiles caused thirsty participants to pour and consume more beverage (Study 1), and increased their willingness to pay and their wanting for more beverage (Study 2). Subliminal frowns had the opposite effect. No feeling changes were observed, even in thirsty participants. The results suggest that basic affective reactions can be unconscious and interact with incentive motivation to influence assessment of value and behavior towards valenced objects.