Emotional Overshadowing: Pleasant and Unpleasant Cues Overshadow Neutral Cues in Human Associative Learning

When learning about stimuli comprised of multiple cues, humans and other animals tend to form stronger cue-outcome associations for more salient cues than for less salient cues. This phenomenon, termed overshadowing, has typically been demonstrated between cues that vary in salience because of differences in physical intensity. In this study, we investigated whether differences in the emotional valence of cues in a compound stimulus similarly led to differences in the strength of cue-outcome learning. Using a probabilistic categorisation task in which stimuli were compounds consisting of pairs of emotional or non-emotional cue images, we found consistent evidence for emotional overshadowing across both an initial exploratory study (N = 50) and a confirmatory preregistered replication study (N = 200). Specifically, both pleasant and unpleasant cue images tended to overshadow neutral cue images, but pleasant and unpleasant cue images did not overshadow one another. Moreover, across stimuli, the magnitude of differences in learning between cues was proportional to differences in their absolute emotional valence, suggesting that attentional capture by both positively and negatively valenced emotions drives overshadowing. These findings have implications for understanding associative learning in natural environments, where stimuli are frequently imbued with emotional valence prior to learning.