We may have seriously underestimated the effects of sleep deprivation. The common belief is that the only cognitive function affected by lack of sleep is attention. However, recent findings by researchers at the University of Michigan reveal that severe sleep deprivation can have more serious effects. Published in the Journal of Experimental Psychology: General, the study found that total sleep deprivation can also impact higher-order cognitive processes, such as decision making. 
To determine the effect of sleep deprivation, the team studied 138 people. Of these, 77 were made to stay awake all night, while the control group of 61 people was sent home to sleep. To check their cognitive functions, the participants had to undertake two separate cognitive tasks. One task measured the reaction time to a given stimulus. In the second task the participants had to complete a series of steps in an exact manner.
The tests were carried out in the evening and then repeated in the morning to check the effect of sleep deprivation on performance. The team found that the error rate doubled from 15 percent to 30 percent in the sleep-deprived group’s performance in the morning. The control group’s performance was largely similar. The researchers concluded that while simple routine tasks can be completed on auto-pilot even when sleep-deprived, the error rate goes up significantly for any task that requires multiple steps or decision making.