Modeling individual differences in cognition

Many evaluations of cognitive models rely on data that have been averaged or aggregated across all experimental subjects, and so fail to consider the possibility of important individual differences between subjects. Other evaluations are done at the single-subject level, and so fail to benefit from the reduction of noise that data averaging or aggregation potentially provides. To overcome these weaknesses, we have developed a general approach to modeling individual differences using families of cognitive models in which different groups of subjects are identified as having different psychological behavior. Separate models with separate parameterizations are applied to each group of subjects, and Bayesian model selection is used to determine the appropriate number of groups. We evaluate this individual differences approach in a simulation study and show that it is superior in terms of the key modeling goals of prediction and understanding. We also provide two practical demonstrations of the approach, one using the ALCOVE model of category learning with data from four previously analyzed category learning experiments, the other using multidimensional scaling representational models with previously analyzed similarity data for colors. In both demonstrations, meaningful individual differences are found and the psychological models are able to account for this variation through interpretable differences in parameterization. The results highlight the potential of extending cognitive models to consider individual differences.     

Effector dynamics of rhythmic wrist activity and its implications for (modeling) bimanual coordination

To examine the role of the effector dynamics of the wrist in the production of rhythmic motor activity, we estimated the phase shifts between the EMG and the task-related output for a rhythmic isometric torque production task and an oscillatory movement, and found a substantial difference (45-52 degrees) between the two. For both tasks, the relation between EMG and task-related output (torque or displacement) was adequately reproduced with a physiologically motivated musculoskeletal model. The model simulations demonstrated the importance of the contribution of passive structures to the overall dynamics and provided an account for the observed phase shifts in the dynamic task. Additional simulations of the musculoskeletal model with added load suggested that particular changes in the phase relation between EMG and movement may follow largely from the intrinsic muscle dynamics, rather than being the result of adaptations in the neural control of joint stiffness. The implications of these results are discussed in relation to (models of) interlimb coordination in rhythmic tasks.     

Person factors associated with suicidal behavior among African American women and men

This study compared person risk factors among the following groups of low-income, African American adults in an urban, public hospital: (a) suicide attempters and nonattempters, (b) male and female attempters, and (c) all 4 groups (50 female attempters, 50 female nonattempters, 50 male attempters, and 50 male nonattempters). Participants completed psychological distress, aggression, substance use, cognitive processes, religiosity/spirituality, and ethnic identity measures. Compared with nonattempters, attempters reported more psychological distress, aggression, substance use, and maladaptive coping strategies; less religiosity/spirituality; and lower levels of ethnic identity. Male attempters endorsed more substance use than female attempters. No person risk factors differentiated among the 4 groups. Assessment of person risk factors and implementation of commensurate culturally competent interventions are recommended.     

Tracking exceptional human capital over two decades

Talent-search participants (286 males, 94 females) scoring in the top 0.01% on cognitive-ability measures were identified before age 13 and tracked over 20 years. Their creative, occupational, and life accomplishments are compared with those of graduate students (299 males, 287 females) enrolled in top-ranked U.S. mathematics, engineering, and physical science programs in 1992 and tracked over 10 years. By their mid-30s, the two groups achieved comparable and exceptional success (e.g., securing top tenure-track positions) and reported high and commensurate career and life satisfaction. College entrance exams administered to intellectually precocious youth uncover extraordinary potential for careers requiring creativity and scientific and technological innovation in the information age.     

Rapid picture presentation and affective engagement

Emotional reactions were assessed to pictorial stimuli presented in a continuous stream at rapid speeds that compromise conceptual memory and the processing of specific picture content. Blocks of unpleasant, neutral, or pleasant pictures were presented at the rate of either three pictures per second or seven pictures per second. Even with rapid presentation rates, startle reflexes, corrugator muscle activity, and skin conductance responses were heightened when viewing unpleasant pictures. These effects were stronger later in the aversive block, suggesting that cumulative exposure increasingly activates the defense system. The findings suggest that, despite conceptual masking inherent in rapid serial visual presentation, affective pictures prompt measurable emotional engagement.     

Pyridostigmine bromide and the long-term subjective health status of a sample of female reserve component Gulf War veterans: a brief report

The role of pyridostigmine bromide (PB) pills in explaining the long-term subjective health status of a sample of over 100 female Reserve Component Gulf War veterans was examined through regression analysis. Results fell just short of significance (p < .06) for the prediction of subjective health approximately six years after the war and were clearly not significant for the prediction of subjective health at previous times. Results parallel Golomb's 1999 RAND report, which found suggestive but not conclusive evidence for the possible adverse effects of Gulf War veterans' consumption of pyridostigmine bromide pills. Our data suggest that use of more than 10 pills may have been especially risky with respect to long-term subjective health.     

Stress-buffering factors related to adolescent coping: a path analysis

To uncover those factors that buffer the impact of stressful negative experiences on adolescent adjustment, a theoretical model of adolescent stress and coping, with social support and social problem solving proposed as moderators, was investigated using path analysis. The study was conducted with 122 ninth-and tenth-grade nonreferred high school students. Using the LISREL statistical package (J?reskog & S?rbom, 1986), it was found that a recursive loop leading from stress outcomes back to negative stressors did not allow for a successful solution to the model. However, the effects of stressful events on adjustment were mediated by coping resources, which included a combination of problem-solving abilities and social support. Overall, the findings replicated previous investigations that have demonstrated direct relationships among stressful life events, social support, problem solving, and adolescent adjustment. While a successful fit to the theoretical model was not attained, it was concluded that a refined model may provide a more acceptable solution.     

Evaluation of a social problem-solving skills program for third- and fourth-grade students

The effects of a social problem-solving (SPS) training program for entire classrooms of third- and fourth-grade children were examined in two studies. In the first study, experimental children showed significantly greater improvement in knowledge and performance of SPS skills than control children. However, both positive and negative effects of the intervention (varying by classroom) were found on measures of behavioral adjustment, self-efficacy, and peer acceptance at a 6-month follow-up. The second study compared two different intervention strategies: (a) SPS training with teacher-student dialoguing, peer pairing, and self-monitoring, and (b) SPS training with dialoguing only. It was found that children in both the experimental and control groups improved significantly in performance of SPS skills but no differences between the groups were found for changes in behavioral adjustment, self-efficacy, and peer acceptance. The limitations of cognitively mediated interventions for young children were discussed.