Cusp catastrophe models for cognitive workload and fatigue: a comparison of seven task types.

The study introduces a nonlinear paradigm that addresses several unresolved problems concerning cognitive workload and fatigue: (a) how to separate the effects of workload versus fatigue, (b) whether the upper boundaries of cognitive channel capacity are fixed or variable, and how multitasking produces a bottleneck phenomenon, (c) that prolonged time on task can produce performance decrements but also produce improvements in task performance associated with practice and automaticity, and that (d) task switching can alleviate fatigue but could be mentally costly. This study describes two cusp catastrophe models that have become useful for separating the workload and fatigue performance phenomena and explores the role of task switching and multitasking in both performance phenomena. In the experiment, 105 undergraduates completed seven computer-based tasks seven times under one of four experimental conditions: tasks fully alternated, tasks aggregated with the multitask module performed first, aggregated with the multitask module performed last, and where the participants chose the task order themselves. Results supported both the cusp models such that fatigue effects were stronger for tasks with higher memory or attentional demand, and were often counteracted by practice effects; spelling ability acted as a compensation variable in most cases, and the intervening amount of work done acted as the bifurcation variable. For cognitive workload, catastrophic shifts in performance were noted between the single tasks and the multitask, with relative difficulty of the single task acting as the load (asymmetry) variable and the flexible task ordering condition as the bifurcation variable.

Cusp catastrophe models for cognitive workload and fatigue in a verbally cued pictorial memory task.

OBJECTIVE: The aim of this study was to evaluate two cusp catastrophe models for cognitive workload and fatigue. They share similar cubic polynomial structures but derive from different underlying processes and contain variables that contribute to flexibility with respect to load and the ability to compensate for fatigue. BACKGROUND: Cognitive workload and fatigue both have a negative impact on performance and have been difficult to separate. Extended time on task can produce fatigue, but it can also produce a positive effect from learning or automaticity. METHOD: In this two-part experiment, 129 undergraduates performed tasks involving spelling, arithmetic, memory, and visual search. RESULTS: The fatigue cusp for the central memory task was supported with the quantity of work performed and performance on an episodic memory task acting as the control parameters. There was a strong linear effect, however. The load manipulations for the central task were competition with another participant for rewards, incentive conditions, and time pressure. Results supported the workload cusp in which trait anxiety and the incentive manipulation acted as the control parameters. CONCLUSION: The cusps are generally better than linear models for analyzing workload and fatigue phenomena; practice effects can override fatigue. Future research should investigate multitasking and task sequencing issues, physical-cognitive task combinations, and a broader range of variables that contribute to flexibility with respect to load or compensate for fatigue. APPLICATIONS: The new experimental medium and analytic strategy can be generalized to virtually any real-world cognitively demanding tasks. The particular results are generalizable to tasks involving visual search.

Long-range prediction of epileptic seizures with nonlinear dynamics.

Patients with uncontrolled epilepsy have some significant problems with planning life routines, and thus one goal of the present study was to explore the viability of predicting seizures in time intervals of one week. The second goal was to utilize the principle of dynamic diseases and to assess the viability of a cusp catastrophe model for seizure onset that was proposed by Cerf (2006). A seizure history of 124 weeks from one adult male patient fit both the cusp and fold catastrophe models (R2 = .92 and .88 respectively) reasonably well using the pdf method and more accurately than counterpart linear models. Prediction of future states was possible, but somewhat compromised because of the nonstationary nature of the data and uncertainties regarding the control variables in the catastrophe models. Analyses of lag functions, however, revealed some surprising elements, suggesting that the precursory conditions for a seizure could be building up over a period of several weeks and that a self-correcting effect within the nervous system could have been occurring.

Stress enhancement of fear learning in mice is dependent upon stressor type: Effects of sex and ovarian hormones.

In three experiments, chronic stress enhancement of subsequent fear learning was investigated in C57Bl/6 mice. The first experiment focused on the influence of stressor type on subsequent Pavlovian fear learning. Male mice were subjected to 7d of either repeated restraint stress or chronic variable stress before undergoing a fear conditioning procedure with three tone-shock trials. Subsequent tests were conducted of contextual and tone fear, through measures of the freezing response. Repeated restraint altered pre-training activity and the unconditional response to shock, but was ineffective in influencing conditional fear. Chronic variable stress significantly inflated contextual fear without altering tone fear. In a second experiment, investigating potential sex differences in the fear-enhancing effects of stress, female mice were subjected to the very same procedures. Among females, chronic variable stress selectively altered tone fear, rather than contextual fear. A final experiment investigated the potential role of ovarian hormones by subjecting female mice to either ovariectomy or sham surgery before the stress procedures. Ovariectomy had no significant effect on the ability of stress to enhance fear in females. In sum, the experiments indicate that stressor type significantly influences subsequent fear learning, that males and females are differentially sensitive to fear enhancement by stress, and that the mechanisms mediating these sex differences lie outside of the immediate influence of ovarian hormones. The findings should allow for refinement of animal models of human psychiatric disorders and for further investigations into the genetic and molecular substrates of significant gender differences in fear and anxiety.