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Mental Workload

Information-intensive work and its effect on people

Digitalisation has fundamentally changed our world of work. Requirements associated with this for acquiring and processing information have consequences for the perceived mental workload. The task of our research is to measure and evaluate this.

Avoiding negative or impairing consequences of mental workload is a precondition for the health of employees. For this purpose, it is necessary to know how high workload caused by mental work actually is. The aim of our research is to measure mental workload over time and evaluate it in order to detect workload peaks.

Determining mental workload with the help of neurophysiological parameters

There are various methods available for measuring mental workload.

Methods for determining mental workload

The methods for determining mental workload can be divided roughly into two categories: subjective and objective evaluation methods. In subjective evaluation methods, questionnaires are used to register the experienced workload. For the objective determination of mental workload, behavioural data and physiological parameters can be gathered and analysed.

Development of an objective method for determining mental workload

Years of research in the USA on analyses of electroencephalograms (EEG), the findings of numerous EEG studies and our own preliminary work are the foundation of the development of a method for the continuous determination of mental workload using an EEG. The findings show that variations in the EEG’s power spectrum in the θ and α frequency bands (4-8 Hz; 8-12 Hz) accompany changes of load level.

Our examinations took place in the shielded laboratory of the Federal Institute for Occupational Safety and Health in Berlin. The 57 subjects who took part in the examination worked on cognitive tasks of varying complexity. Their brain activity was recorded while they were doing this.

The examinations confirm the tendencies generally known from the literature that increasing difficulty of tasks is accompanied by an increase in the power spectrum of the frontal θ band and a decrease in the power spectrum of the parietal α band. They form the basis for our own approach on the development of the new objective method.

The chart illustrates the principle of the new method for indexing mental stress. Principle of the new method for indexing mental stress

Measuring mental workload on the basis of electroencephalography has one advantage: workload is measured where information processing takes place, namely the brain. Preliminary work on the development of a method for determining mental workload continuously is carried out in the framework of research by the Federal Institute for Occupational Safety and Health.

Measuring mental workload under realistic conditions

Measuring mental workload with the help of the EEG presupposes interference-free recording. Good signal quality is only possible in this way. Furthermore, it is also important to use user-friendly EEG measuring systems. For this purpose, marketable devices must be tested with regard to usability, user-friendliness and acceptance.

EEG systems used in the study (from top left to right): Ladybird, Sahara, EPOC, Trilobite, Jellyfish, BR 8 plus and MindCap Mobile EEG recording systems

Examination of the usability of mobile EEG devices

Within the framework of a research project, the BAuA is testing seven EEG recording systems that are currently available on the market.

Testing is being carried out of:

  • the application time of the electrodes,
  • the learning effort for operating the recording systems,
  • the possible wearing time and the comfort of the new EEG electrode systems.

Another important criterion is the design of the EEG headsets, i.e. their ability to adapt to different head shapes to assure a good contact of the electrodes with the surface of the head. This is necessary to derive the EEG with as few artefacts as possible.

The aim of the examinations is to identify EEG recording systems that affect the user least of all. This ensures a good quality of the results due to fewer secondary effects during EEG recording.

Validating the method for determining mental workload

Validation of the method for determining mental workload is carried out in cooperation with the Department for Controller Assistance at the Institute of Flight Guidance, DLR Braunschweig. In an interactive simulation, this project focuses on arrival management, that is, on approach control. Approach controllers are responsible for pilots keeping to the stipulated flight altitudes. They are also responsible for aircrafts starting to land at a suitable rate.

To which extent the method developed by the BAuA for continuous mental workload registration can differentiate reliably between different simulated stress level conditions must be checked. Researchers use already known rules and regulations for air traffic controllers to simulate stress situations at different levels realistically.

For practical use, it must be shown that the new method can differentiate among the different workload states reliably and correctly. This method’s test is carried out at the German Aerospace Centre (DLR) in Braunschweig.
In the long term, the method is to be employed to record mental workload continuously during information-intensive work conditions.