Evaluating methods for approximating stochastic differential equations

Models of decision making and response time (RT) are often formulated using stochastic differential equations (SDEs). Researchers often investigate these models using a simple Monte Carlo method based on Euler's method for solving ordinary differential equations. The accuracy of Euler's method is investigated and compared to the performance of more complex simulation methods. The more complex methods for solving SDEs yielded no improvement in accuracy over the Euler method. However, the matrix method proposed by Diederich and Busemeyer (2003) yielded significant improvements. The accuracy of all methods depended critically on the size of the approximating time step. The large (∼10 ms) step sizes often used by psychological researchers resulted in large and systematic errors in evaluating RT distributions.     

Categorization Deficit in Old Age: Reality or Artefact?

When categorization behaviour is compared between young and elderly adults, results usually show a decrease in taxonomic choices along with an increase in thematic choices. This can be interpreted in two ways: a decline in the ability to perceive and use taxonomic relations, or a modification of conceptual preferences with aging related to a bias stemming from material which favours young adults. We evaluated the second hypothesis by studying whether the salience of categorical associations could explain the differences generally observed between young and elderly adults. This hypothesis was tested on 25 young subjects (M = 45.3 years, SD =5.6 years) and 30 elderly subjects (M = 71.5 years, SD = 7.1 years) using a matching task: individual judgments were used to build triads in which a target was presented along with a strong and a weak associate. In line with our hypothesis, both age groups were influenced by associative strength and type of relation in the same way. Results are interpreted with Baltes’s [1987, Developmental Psychology, 23, 611–626] model.     

Life-Satisfaction in Post-Soviet Russia and Ukraine

This paper fills a gap in the literature by looking at influences on the well-being of the citizens of Russia and Ukraine in the context of the triple shock – economic, political and social – that they experienced after 1991. The paper argues that lived experience – how people evaluate their living conditions – is as significant an influence on the welfare of citizens as are the actual conditions in which they live. The majority of the populations perceive the post-1991 economic and political changes negatively, and levels of general satisfaction and happiness are comparatively low. The findings suggest that objective economic factors, geographical/social location, health status and social context influence well-being, but also personal control and satisfaction with material circumstances, with health having a greater influence on happiness, while material circumstances and the evaluation of them have a greater influence on general satisfaction. The paper concludes by arguing for a model of reciprocal causation in which material factors provide the partially determining context for actions and are themselves influenced by happiness and satisfaction.     

The effect of informational stimuli on instrumental response rate: Signalling reward versus signalling the availability of reward

Rats were trained to press a lever for food on an interval schedule and were given a brief cue (0.5 sec) between the operative response and the reward (C condition). Some control subjects in Experiments 1, 2 and 4 were given their cue either following the end of the temporal interval during which reward had been unavailable (SD condition), or randomly with respect to food (R condition). Other control subjects in Experiments 2 and 4 received both the food-correlated cue and the temporal-interval stimulus (B condition). In all experiments, rate of responding was lowest for the C subjects and for B animals when the two cues were from different modalities. Food-correlated and temporal-interval cues did not interact, suggesting that a reward-correlated signal does not affect response rate simply by enhancing the salience of the temporal interval offset.