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

The present study examines whether monitoring and control behaviour ar e affected by sleep loss and fatigue. The effects of one night of slee p loss are investigated in a dual-task consisting of a monotonous trac king task that requires continuous control behaviour and a time estima tion task that requires monitoring with an 'open-loop' character. In t he 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 estima te consecutive time intervals and to respond when an interval had ende d. There were three experimental conditions. In the first condition a clock was presented continuously on the screen; thus, subjects had a c lear notion of the time course. In the second condition subjects could obtain time information by pressing a key. In the third condition sub jects could not obtain time information, but the status of the time in terval could be obtained by pressing a key; that is, information was g iven whether a time interval had ended or not. The present study confi rms earlier findings that tracking performance is sensitive to sleep l oss particularly towards the end of the half hour working session. In contrast, time estimation performance was not impaired, although subje cts tended to make more observations when deprived of sleep. This resu lt would not have been expected on the basis of a decreased level of a ctivation due to sleep loss. It appears, however, that checking the ti me course with a motor response requires less effort than continuously updating an internal clock, which puts heavy demands on working memor y. The observed difference between the tasks with respect to the vulne rability to sleep loss is explained in terms of their motivating prope rties.