Fig. 2. Study procedures and serial reaction time task.

A) On each experimental day, participants first completed the encoding phase of the SRTT, followed by a nap or wake interval (within-subject, separated by 1 week, order counterbalanced), then completed the delayed test phase of the SRTT. During each phase of the SRTT, participants practiced the task in the mock MRI to criterion and completed the SSS prior to beginning the experimental MRI session. Additional questionnaires and sequence awareness assessments were completed after the delayed test phase of the SRTT on each day (*Post: in-house questionnaires regarding dexterity). B) The SRTT utilized a four-button MRI-compatible response box and images were presented on a screen visible to the participant, who was supine in the scanner. Participants were instructed to respond quickly and accurately to stimuli (the location of the white box in a row of four boxes). C) In the MRI scanner, experimental blocks alternated between sequential (S) and random (R) stimulus order. Twelve blocks with 40 stimuli each were performed in each task phase. Skill learning was assessed as the performance in a given sequence block relative to the following random block, and across-interval performance was assessed as a change score comparing the second block-pair of the delayed test phase to the average of the final two block-pairs of the encoding phase.