Pigeons concurrently categorize photographs at both basic and superordinate levels

We studied categorization in pigeons, using carefully controlled photographs. Within daily sessions, 4 pigeons had to classify each of 32 photographs into either its proper basic-level category (cars, chairs, flowers, or people; four-key forced choice procedure) or its proper superordinate-level category (natural or artificial; two-key forced choice procedure). The pigeons successfully classified the same stimuli at both levels. Overall, the pigeons learned the basic discrimination more quickly than the superordinate discrimination, but this difference was reliable only for artificial stimuli (cars and chairs), not for natural stimuli (flowers and people). The pigeons also exhibited reliable discrimination transfer to novel photographs, attesting to the open-endedness of these basic and superordinate categories.     

Examining the Role of Peer Influence and Self-Control on Downloading Behavior

In the Chilean school system, classrooms are stable settings and constitute a closed socialization context. Through multilevel analysis, this article examines the association between classroom composition and students' marijuana consumption. Under the theoretical assumption that social control mechanisms work into social learning peer processes, our results indicate that, as an imposed environment, the classroom may encourage or discourage marijuana use among students. The results suggest that individual marijuana use is strongly associated with school bonding and marijuana tolerance at the classroom level. The strength of these associations depends on the flexibility and stability of the classroom structure.     

Is Traditional Gender Ideology Associated with Sex-Typed Mate Preferences? A Test in Nine Nations

Social role theory (Eagly, Wood, & Diekman, 2000) predicts that traditional gender ideology is associated with preferences for qualities in a mate that reflect a conventional homemaker-provider division of labor. This study assessed traditional gender ideology using Glick and Fiske's (1996, 1999) indexes of ambivalent attitudes toward women and men and related these attitudes to the sex-typed mate preferences of men for younger mates with homemaker skills and of women for older mates with breadwinning potential. Results from a nine-nation sample revealed that, to the extent that participants had a traditional gender ideology, they exhibited greater sex-typing of mate preferences. These relations were generally stable across the nine nations.     

Tie strength and family formation: Which personal relationships are influential?

On the basis of the analysis of qualitative interviews in Western Germany, it has been argued that personal relationships have a strong impact on individuals' family formation processes and childbearing intentions. Persons who influence individuals' childbearing choices were identified. Strong ties, such as among core family members (i.e., parents and siblings), are an important contributing factor, but the authors are also able to show that weak ties, such as those among colleagues and acquaintances, need to be considered when examining social influence on family formation processes. Apart from single network partners, influential groups of persons have been identified. Such groups serve as a comparative standard regarding the timing of having one's first child and subsequent children.