Demanding work settings often require the deferral of intended actions. In 3 experiments, participants were to withhold a response until they encountered a task change (which occurred 5, 15, or 40 s later). To approximate highly demanding settings, the experimenters sometimes divided attention during the delay period. During some of the delays the experimenters interrupted the participants with an additional task (Experiment 1). Demanding conditions as well as interruptions revealed rapid forgetting of intentions at levels that would be considered significant in applied settings. Experiments 2 and 3 showed that this rapid forgetting was not reduced by strategic rehearsal and implementation intention strategies. The results suggest that maintaining intentions over brief delays is not a trivial task for the human cognitive system.

In contrast to many phenotypes that have been studied using twin designs, substance use shows considerable evidence of environmental influence. Accordingly, specifying the relevant environments and understanding the nature of their effects is an important research priority. Twin studies also have demonstrated that the importance of genetic and environmental influences varies across development for a variety of behavioral outcomes, including substance use. Here, we report analyses exploring moderating effects associated with parenting and peer characteristics on adolescent smoking and drinking, measured at ages 14 and 17. We find significant evidence of moderating effects associated with two dimensions of parenting (parental monitoring and time spent in activities with parents) on adolescent smoking, measured at two time points across development, but no moderating effects on adolescent drinking. Genetic influences on smoking increased, and common environmental effects decreased, as adolescents reported less parental monitoring and spending more time with their parents. Conversely, we find evidence that adolescent drinking is more strongly influenced by peer characteristics. The importance of genetic predispositions was increased among adolescents who reported more friends who used alcohol. These analyses illustrate the importance of incorporating measured aspects of the environment into genetically informative twin models to begin to understand how specific environments are related to various outcomes. Furthermore, they illustrate the importance of using a developmental perspective to understand how specific influences may vary across different ages, and across different phenotypes.

The progression to alcohol dependence unfolds across multiple stages, including the decision to initiate use, the development of regular patterns of use, and (for some individuals) the subsequent development of problems associated with alcohol use. Using data from two population-based, longitudinal twin studies, FinnTwin16 (FT16) and FinnTwin12 (FT12), we applied multiple stage genetic models (Heath et al., Twin Res. 5 (2002) 113) to better understand the extent to which genetic and environmental influences impact the initiation of alcohol use, frequency of use in adolescence and young adulthood, and alcohol problems in young adulthood. Shared environmental factors played a large role in initiation, and a more moderate role on frequency of use, and it was largely the same influences acting across these stages of use. However, there was no significant evidence of shared environmental influences on alcohol problems in early adulthood. Problems were largely influenced by genetic factors that overlapped with genetic influences on frequency of use. Unique environmental factors were largely specific to each stage, with some overlap between alcohol problems and frequency of use at age 25.

Gender and gender of friends moderate the associations between friends' behavior and adolescents' alcohol use, with evidence that girls, and those with opposite-sex friends, may be more susceptible to friends' influence. Genetically informative analyses suggest that similarity in alcohol use between adolescents and their friends is mediated, at least partially, through environmental pathways.