In this study, subjects were shown two sets of 12 color photographs of people’s faces (24 in total). Five minutes after seeing the last one, the subjects were then shown another 48 faces (one by one, as before) and had to say whether or not they had seen the face earlier. If so, they were asked whether they saw it in the first or second set of photographs. Half the subjects had been deprived of sleep for the previous 35 hours. Some of these had been given significant amounts of caffeine to offset their sleepiness.
It was found that the sleep-deprived subjects, whether or not they had had caffeine, were as good as the non-sleep-deprived subjects at recognizing which faces they had seen before. However, the sleep-deprived subjects were significantly worse at remembering which set the faces had appeared in. This occurred even though otherwise optimum conditions for recall existed (the test was novel, stimulating, and relatively short; it was given at the best time of day for maximum alertness).
Caffeine significantly reduced the feelings of sleepiness and did appear to improve the ability of the sleep-deprived subjects to remember which set the face had appeared in, but the level of recall was still significantly below the level of the non-sleep-deprived subjects. Caffeine made no difference to the memory performance of subjects who were not sleep-deprived.
Interestingly, sleep deprivation increased the subjects’ belief that they were right, especially when they were wrong. In this case, whether or not they had had caffeine made no difference.
It may be that the problem with temporal memory reflects a more general problem with remembering context information.
Recognition memory for faces was unaffected by being deprived of sleep for 35 hours.
However, sleep-deprived subjects were significantly worse in remembering in which of two sets of photos particular faces had appeared in.
Sleep-deprived subjects who had been given significant doses of caffeine remembered the set better than those who had not, but were still poorer at remembering than those not deprived of sleep.
Although their performance was poorer, sleep-deprivation seemed to increase the subjects' belief in their own accuracy.
It seems likely that sleep-deprivation affects memory for context.
Harrison, Yvonne & Horne, James A. 2000. Sleep loss and temporal memory. The Quarterly Journal of Experimental Psychology, 53A (1), 271-279.