Emotion affects similarity via social projection.

Given the ubiquity of emotional experiences and the importance of similarity for understanding cognition and behavior, we examined how emotional valence affects perceived similarity. We hypothesized an affective projection process, whereby the emotion evoked by a prime is projected onto and influences judgments of unrelated targets. Experiment 1 revealed that positive events were judged more likely after a positive prime (“respected”) than after a negative prime (“rejected”), thus demonstrating affective projection, whereas negative events were judged equally likely regardless of prime valence. Across five further experiments, positive primes increased similarity ratings of unrelated social categories (musicians & dentists), animals (penguins & horses), and animal-like novel figures (greebles). In contrast, because emotions cannot be projected onto inanimate objects, judgments of artifacts (saws & spoons) and artifactlike figures (yadgits) were unaffected. The influence of prime valence on target judgment was asymmetric, with positive primes affecting similarity but negative primes having no effect