Sleep deprivation, whether it is total sleep deprivation or partial sleep deprivation, can impair working memory in measures of memory, speed of cognitive processing, attention and task switching. Casement et al. found that when subjects were asked to recognize digits displayed on a screen by typing them on a keypad, the working memory speed of subjects whose sleep was restricted to four hours a night (approximately 50% of their normal sleep amount) were 58% slower than control groups who were allowed their full eight hours of sleep.[33]