THE EFFECTS OF SLEEP LOSS IN A COMBINED TRACKING AND TIME-ESTIMATION TASK

The present study examines whether monitoring and control behaviour are affected by sleep loss and fatigue. The effects of one night of sleep loss are investigated in a dual-task consisting of a monotonous tracking task that requires continuous control behaviour and a time estimation task that requires monitoring with an 'open-loop' character. In the tracking task subjects had to keep a square cursor in the centre of a U-shaped target. In the time estimation task subjects had to estimate consecutive time intervals and to respond when an interval had ended. There were three experimental conditions. In the first condition a clock was presented continuously on the screen; thus, subjects had a clear notion of the time course. In the second condition subjects could obtain time information by pressing a key. In the third condition subjects could not obtain time information, but the status of the time interval could be obtained by pressing a key; that is, information was given whether a time interval had ended or not. The present study confirms earlier findings that tracking performance is sensitive to sleep loss particularly towards the end of the half hour working session. In contrast, time estimation performance was not impaired, although subjects tended to make more observations when deprived of sleep. This result would not have been expected on the basis of a decreased level of activation due to sleep loss. It appears, however, that checking the time course with a motor response requires less effort than continuously updating an internal clock, which puts heavy demands on working memory. The observed difference between the tasks with respect to the vulnerability to sleep loss is explained in terms of their motivating properties.