Verslag over het jaar 1975 - TNO Nederlands instituut voor Preventieve Geneeskunde
Annual report 1975 TNO organistaion The Netherlands
The project's title indicates clearly that mental load can be the result of the situation in which one finds oneself. Mental load is said to occur if a situation requires the processing of a good deal of information, and/or when stimuli causing 'emotion' (for instance social pressure, conflicts, danger) are present. The objective of this project is to develop instruments for measuring mental load in the human being and to test their usefulness.
The phenomena to be studied in this connection are variables of a physiological and of a behavioural nature (for instance through the ECG and by means of a binary choice task respectively).
The study is done in experimentally controlled field situations in which the 'load' requires a minimum amount of physical energy and a maximum of mental effort. The factors expected to vary with mental load are the experimental variables (predictors) for this study; the criterion is constituted by the experimental conditions. Experiments are carried out in which emotional mental loading is studied (for example in parachutists and divers working under dangerous conditions) and experiments stressing information processing (pilots).
The experiments with pilots are carried out in co-operation with the KLM, the National Center for Aeronautic Medicine and the Government Aviation school. The study of divers is conducted together with the medical center for divers of the Royal Navy, the study of parachutists with the Commando Troops at Roosendaal and the Free University of Amsterdam. The studies are set up in such a way as to have a more general scientific relevance as well as practical usefulness.
The results of the experiments on physiological variables exemplify the possibility to roughly differentiate between levels of mental load in field situations, such as flight procedures of varying degree of complexity. respiration rate, sinus a-rhythmia and heart rate differ significantly (p=0.001) between descent, start, horizontal flight and rest. Respiration rate was the most sensitive measure, descent was the most heavily loading condition and so on.
As was predicted a study of emotional mental load in parachutists conducted for comparison - showed heart rate as the most sensitive measure.
From these studies it became clear that considerable differences in patterns of reactions to situations exist between individuals; it was as yet not possible to account for the smaller differences in mental load. (Residual) information processing capacity is determined by means of the binary choice-generators in experimentally controlled loading conditions. The use of this residual capacity as a measure for mental load is studied. Till now studies in this line were carried out on pilots (in several stages of the flight), air traffic controllers (a simulator in several stages of the flight), firemen (on ladder-towers) and divers during escape from below-surface tanks and at great depth. Results proved that it is possible for people to perform a binary choice task under these complex conditions. Task performance is according to expectations: quality decreases with the increase of loading.
At present studies with the binary choice generator are in progress in the Royal Navy. The toxic effect of air under high pressure (10 atmosphere) on divers in a wet decompression chamber is determined.
The technique which was developed enables the observer outside the chamber to receive a direct indication of the subject's vigilance level through a continuously recording registration device. This technique is also suitable for the study of the effect of under-pressure as is done on pilots in the chamber of the National Center for Aeronautic Medicine at Soesterberg.
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