We investigate how the complexity of the social environment (more vs. less groups) influences attitude formation. We hypothesize that facing a larger number of groups renders learning processes about these groups noisier and more regressive, which has two important implications. First, more-complex social environments should lead perceivers to underestimate actual group differences. Second, because most people usually behave positively, more-complex social environments produce negatively biased attitudes and cause perceivers to overestimate the frequency of "negative" individuals among groups. We tested these predictions in five attitude formation experiments (N=2,414). Participants' attitudes and learned base rates of positive and negative group members proved more regressive in complex social environments, that is, with multiple groups, compared with less-complex environments, that is, with fewer groups. In a predominantly positive social environment, this regression caused participants to form more negative group attitudes and more strongly overestimate negative individuals' prevalence among groups.
Keywords: attitudes; complexity; memory; social cognition.