Experimental procedure.

<p>The experiment consisted of a <i>Training</i> followed by a <i>Retrieval</i> session. Sleep group (<i>SG</i>), nighttime-awake group (<i>NA</i>) and daytime-awake group (<i>DA</i>) performed a dual task (concomitant SRTT and WPAT; upper part). The daytime-awake-subsequent-WPAT group (<i>DAs</i>) performed a single task (SRTT alone then followed by the WPAT; lower part). <i>Training session (left part)</i>. SRTT was arranged in blocks (in yellow), for which the trial sequence was <i>fixed</i>, followed by blocks (in green) with <i>random</i> sequences of trials. Numbers in the bottom mark block’s position in the general sequence whereas, numbers on the top indicate the number of trials administered within each block. “Practice” (light blue) indicates the initial practice block, which was not included in the analyses. The WPAT (distractor task) was continuously performed throughout the entire SRTT session. The first and the last fixed sequence blocks (i.e.: block 2 and block 6), followed by the random sequence block 3 and 7, respectively were considered to investigate changes in performance across <i>Training</i>. For clarity, block 2 and block 3 were labeled as “Training 1” whereas block 6 and block 7 were labeled as “Training 2”. The difference between mean RTs to random and sequential blocks was the dependent variable being analyzed. <i>Retention interval between training and retrieval sessions (middle part)</i>. The sleep group slept the two nights after <i>Training</i> before doing <i>Retrieval</i> in the morning. The nighttime-awake group, instead, stayed awake throughout the first night after <i>Training</i> and slept the second night. The daytime-awake group trained in the morning and was retested in the evening of the same day during which they stayed awake. <i>Retrieval session (right part)</i>. Block 9 (fixed trial sequence) and block 10 (random trial sequence) were labeled as <i>Retrieval</i>. The same random minus fixed block difference as in the training session was taken to investigate the RT performance. The task was immediately followed by one bock (in purple) in which a generation task was administered.