群体印象形成与个体印象形成：反基准比率效应

采用 “反基准比率效应”范式考察在群体印象形成与个体印象形成两种认知加工过程中, 基准比率对印象形成过程及其结果的影响。被试分别为39名19~25岁大学生(实验1：男生17名, 女生22名, 均为右利手)以及46名19~25岁大学生(实验2：男生21名, 女生25名, 均为右利手)。结果发现：无论是群体印象形成还是个体印象形成, 在学习阶段, 知觉者都能准确认知各类事件间的关系, 但会优先建构高频事件间的联结。而在测试阶段, 当低频事件与高频事件同时出现时, 知觉者发生明显关系误判, 即以反基准比率的倾向高估低频事件间的联结强度。实验表明群体与个体印象形成过程中都会产生反基准比率效应这样的加工偏差, 进而初步揭示反基准比率现象在社会信息加工领域具有一定的普遍性。

Perceiving Groups and Persons:Inverse Base-Rate Effect

Hamilton and Sherman (1996) argued that forming an impression of an individual and developing a conception of a group were governed by the same fundamental information-processing system, while researchers didn’t find adequate evidences supporting this argument. According to the Inverse Base-Rate Effect (IBRE) (Medin & Edelson, 1988), Sherman et al. (2009) discovered the base-rate of different kinds of cues had an impaction on stereotype formation. In addition, similar phenomenon was found in person perception. Based in these ideas and findings, this research sought to investigate whether the impaction modes of base-rate on the perception of groups and persons would be the same using IBRE design. Two experiments provided evidences for the above hypothesis. In experiment 1, the impression formation targets were groups, and 39 Chinese undergraduates participated, and the experiment design was the same to experiment 1 of Sherman et al. (2009) except Chinese materials. In experiment 2, the targets were individuals and there were 46 participants. Based on IBRE problem construct, the basic design involved a pair of persons, designated an acquaintance and a stranger. The acquaintance and the stranger occurred with a 3:1 base ratio. The acquaintance was characterized by two traits labeled by PC and I (PC was a perfect predictor of the common group, and I was an imperfect predictor), and the stranger was also characterized by two traits labeled by PR and I (PR was a perfect predictor of the rare group). PC was the perfect trait of the acquaintance, which always predicted the acquaintance and never the stranger; and PR was the perfect trait of the stranger, which always predicted the stranger and never the acquaintance; and I was an imperfect predictor of the two individuals in that the acquaintance and the stranger were both associated with this trait. The experiment was comprised of 2 basic designs. Participants were asked to engage in an impression formation task. During training, participants were asked to judge different persons from patterns of traits, and given feedbacks. Following training, participants were tested with combinations of traits not shown during training, which were PC, PR, I, PC+PR, PC+PR+I. The result of experiment 1 was consisting with the one of (Sherman et al., 2009), in which participants showed strong selection preference for a minority group. Results of the experiment 2 showed: firstly, base-rate information were learned and consistently applied to training and testing cases. Secondly, the frequent traits (PC and I) and the acquaintance were learned earlier than the infrequent trait (PR) and the stranger, so that the former ones were encoded by his typical features and the infrequent targets were encoded by his distinctive features, which resulted in the Inverse Base-Rate Effect (IBRE). In conclusion, whatever the impression formation targets were groups or individuals, information base-rate would influence the cognition processes and lead similarly progressing bias. The Inverse Base-Rate Effect might be a general phenomenon in social cognition.