Peer-Reviewed
Frontal theta changes as precursors of performance breakdown in manual process control: evidence for markers of cognitive strain and executive fatigue?
A.C. Roberts
University of Sheffield
P. Nickel
University of Sheffield
G.R.J. Hockey
University of Sheffield
Background
In performance tasks where goal maintenance is critical (such as safety critical systems) the threat from periods of high demands or stressors can normally be offset by compensatory control mechanisms (originating in the central executive) that allow performance to be maintained through increased effort. However, there is likely to be a limit to the capacity for high effort compensatory regulation under cognitive strain, such that fatigue of executive function may lead to manifest breakdown, with serious operational consequences. Identification of these strain (high risk) states would minimise the risk of breakdown by providing opportunities for intervention before errors occur. A candidate marker for strain is theta band EEG activity in the prefrontal cortex, shown in a number of studies to be a likely index of executive function.
Methods
We used a simulated decision-making and process control task, with a cyclic loading method to force performance breakdown (occurrence of control errors) through stepwise increases in manual control load. Psychophysiological data (EEG & ECG) were collected and analysed in relation to changes in primary and secondary task performance measures.
Results
As anticipated, theta band power increased with control load, indicating its sensitivity to demand level. However, a further time series analysis of theta power and performance also indicated that the (infrequent) occurrences of control error were usually preceded by shifts in theta power over the preceding few minutes. Most participants showed a decrease in theta, while some showed an increase. A current analysis suggests that this difference may reflect variations in strategies for compensatory regulation and effort management.
Discussion
The findings suggest that theta band activity in the prefrontal cortex may be used as a marker of high risk states, and a short-term predictor of performance breakdown. It is argued that such changes may result from an interruption in the top-down control of task goals from short-term fatigue developed during the high strain conditions generated by the cyclic loading method.
