Conditioning of two-response patterns of key pecking in pigeons

On discrete trials, two response keys were made available to hungry pigeons and food reinforcement depended on the order in which the required two key pecks occurred. In different phases, only one of the four possible two-peck sequences (left-left, left-right, right-left, and right-right) produced food reinforcement. In each case, the pigeons learned to perform the correct two-peck sequence more often than the incorrect sequences. Furthermore, the course of differentiation mastery indicated that both reinforcement history and response-reinforcer contiguity influenced performance. These results reveal that response patterns comprising two instances of the same response left-left and right-right) or instances of two different responses (left-right and right-left) may function as operants, thereby extending the generality of conditioning principles from discrete responses to structured sequences of behavior. These and other results are discussed in terms of contiguity-based and memory-based models of learning.     

Witnessed community violence and antisocial behavior in high-risk, urban boys

Examined the longitudinal relation between children's self-report of witnessing community violence, family environment, and parent report of child antisocial behavior in a sample of 6- to 10-year-old urban American boys (N = 97) at familial risk for antisocial behavior. Boys reported high rates of lifetime exposure to community violence. Boys' reports of witnessing community violence were significantly positively related to changes over 15 months in child antisocial behavior, even after controlling for the possible effects of 3 aspects of parent-child interactions shown previously to be related to problematic child behavior. Furthermore, family environment, particularly the degree to which parents engaged in conflict with their sons, moderated the effect of witnessed violence on changes in antisocial behavior. In families with low conflict, higher levels of witnessed violence predicted increases in antisocial behavior over time. In contrast, in families with relatively high levels of parent-child conflict, high-witnessed violence had no additional influence on antisocial outcome. This is the first prospective longitudinal study to document an association between witnessed community violence and changes in antisocial behavior in young, urban boys at familial risk for antisocial behavior.     

Logit models and logistic regressions for social networks: III. Valued relations

This paper generalizes thep* model for dichotomous social network data (Wasserman & Pattison, 1996) to the polytomous case. The generalization is achieved by transforming valued social networks into three-way binary arrays. This data transformation requires a modification of the Hammersley-Clifford theorem that underpins thep* class of models. We demonstrate that, provided that certain (non-observed) data patterns are excluded from consideration, a suitable version of the theorem can be developed. We also show that the approach amounts to a model for multiple logits derived from a pseudo-likelihood function. Estimation within this model is analogous to the separate fitting of multinomial baseline logits, except that the Hammersley-Clifford theorem requires the equating of certain parameters across logits. The paper describes how to convert a valued network into a data array suitable for fitting the model and provides some illustrative empirical examples.This research was supported by grants from the Australian Research Council, the National Science Foundation (#SBR96-30754), and the National Institute of Health (#PHS-1RO1-39829-01).     

COMPARATIVE COGNITION:

Abstract— Human and nonhuman animals alike must adjust to complex and ever-changing circumstances if they are to survive and reproduce. Advanced neural mechanisms enable animals to remember the past, to act in the present, and to plan for the future. Exploring the species generality of cognitive processes in behavior is central to the field of comparative cognition. A comparative perspective may not only broaden but also deepen our understanding of cognition—both in human and in nonhuman animals.     

¿Qué? Quoi? Do Languages with Grammatical Gender Promote Sexist Attitudes?

Languages such as French and Spanish assign a gendered article to nouns. Three experiments examined whether reading a language with grammatical gender would increase sexist attitudes. Suburban, New York high school students (N?=?74, 85, 66) were randomly assigned to complete a survey of sexist attitudes in either English or a language with grammatical gender (French or Spanish). Students in the English condition expressed less sexist attitudes than students in the French or Spanish conditions, and the language used affected females more than males. When the experiment was replicated on bilingual students, similar results were found. Males also expressed more sexist attitudes than females. This study suggests that languages with grammatical gender promote sexist attitudes and have particular impact on females.     

A theory of variability discrimination: Finding differences

Visual variability discrimination requires an observer to categorize collections of items on the basis of the variability in the collection; such discriminations may be vital to the adaptive actions of both humans and other animals. We present a theory of visual variability discrimination that aggregates localized differences between nearby items, and we compare this finding differences model with a previously proposed positional entropy model across several data sets involving both people and pigeons. We supplement those previously published data sets with four new experiments, three of which involve arrays comprising items entailing systematic, quantitative differences. Although both theories provide strong and similar fits of the published data sets, only the finding differences model is applicable to investigations involving quantitative item differences, providing excellent fits in these new experiments.     

The association between life events and suicide intent in self-poisoners with and without a history of deliberate self-harm: a preliminary study

The associations between life events in the 12 months preceding an episode of self-poisoning resulting in hospital attendance (the index episode), and the suicide intent of this episode were compared in individuals for whom the index episode was their first, episode and in individuals in whom it was a recurrence of DSH. Results indicated a significant interaction between independent life events, repetition status, and gender in the prediction of suicide intent, the association between life events and intent being moderated by repetition status in women only. The results provide preliminary evidence to suggest the presence of a suicidal process in women, in which the impact of negative life events on suicide intent diminishes across episodes.