Figure 4.

Sleep restriction impaired recall of massed items. Students who were exposed to either 9 h of time in bed (TIB) or 5 h of TIB for sleep used digital flashcards to study Graduate Record Examination (GRE)-type words on 4 consecutive days (i.e., the study phase of the experiment, indicated by the gray boxes). In the massed study condition, a different set of 5 word pairs was presented on each day (Set 1 – day 4; Set 2 – day 5; Set 3 – day 6; Set 4 – day 7) and studied only once, with 8 repetitions per flashcard. For the first set of massed items that was studied, the time course of cued recall performance was similar between sleep groups. In contrast, test scores for massed items shown during the other study sessions were consistently worse in adolescents exposed to sleep restriction. There was a significant interaction between Set and TIB (LR χ² = 10.71, P = 0.013), in which students who were exposed to sleep restriction showed significantly lower test scores for massed items presented in Sets 2 and 3 after all items had been studied (indicated by red asterisks, P < 0.05). Additional statistical comparisons are presented in the main text. For each set of massed items, “S” indicates recall performance immediately after each set of items was studied. The mean ± SEM is shown for performance on each cued recall test.