Serial Reaction Time Task (SRTT)

Participants completed the SRTT (Nissen and Bullemer, 1987) in two test sessions. In one session, participants completed the task before and after a 90-min afternoon nap session (this session is hereafter referred to as the “Nap” session). In another session, the task was completed before and after a period of sustained wakefulness (this session is hereafter referred to as the “Wake” session). On average, each session was separated by a 15-day interval (FOC Group: M = 15.86 days, SD = 14.67; SOC Group: M = 19.43 days, SD = 23.19).

The SRTT was divided into a learning phase and a retention phase. A period of approximately 2-h separated each phase of the task. The learning phase was presented before a delay period of napping or wakefulness, depending on the session type, followed by the retention phase. The learning phase comprised six blocks of trials, hereafter labeled Blocks 1–6, respectively. A single trial commenced with a blank computer display (“22” Lenovo ThinkVision T2254pC monitor) for a duration of 150 ms. Next, a visual stimulus appeared for 650 ms in one of four predefined spatial locations presented in a diamond shape around the center of the monitor. Participants were provided with a response pad (Logitech Precision Wired PC Gamepad; Logitech, Lausanne, Switzerland) with four buttons that were also arranged in a diamond configuration. Participants were instructed to press the button on the response pad that matched the location of the visual stimulus. The visual stimulus appeared on the computer display for 650 ms irrespective of whether a response was made. An overview of the task is presented in Figure 2.

Overview of the Serial Reaction Time Task used in the study. (A) Shows the location that the visual stimulus could appear on each trial and the response panel used. (B) Provides timing details on a single trial.

Unbeknownst to participants, on Blocks 2, 3, 4, and 5, the location that the visual stimulus appeared on each trial followed a pre-determined sequence. These blocks are hereafter referred to as “Sequence Blocks.” Block 1 was a practice block which served to familiarize participants with the task and consisted of 60 trials. On this block the visual stimulus appeared randomly in one of the four locations. All other blocks consisted of 96 trials. Block 6 was the “Random Block.” On this block, the visual stimulus appeared pseudo-randomly in one of the four spatial locations adhering to the constraints that they (a) always began at location “1” and (b) did not contain five or more stimuli locations which matched the sequence used in that session.

Participants were presented with the same type of sequence (i.e., FOC or SOC sequence) in both the sleep and wake sessions. However, a different FOC and SOC sequence was used in each of the sessions. Thus, in total, four different sequences were used in this study. Participants were presented with two FOC sequences (one in the Nap session and the other in the Wake session) or two SOC sequences (one in the Nap session and the other in the Wake session). Labeling the left-most position that the visual stimulus could appear on the screen as “1,” the lower most position as “2,” and so on, the sequences presented to participants were as follows:

The presentation order of the different FOC and SOC sequences within each group was randomized by a coin-toss before commencing the learning phase of the SRTT on the first session.

The retention phase of the SRTT comprised three blocks of 96 trials. This part of the task was administered after the nap or wakeful period. Blocks 7 and 9 were the Sequence blocks. On these blocks, participants were presented with the same FOC or SOC sequence used on the learning phase of the task. Block 8 comprised the Random block in which the visual stimulus appeared in pseudo-random positions using the same constraints described above as for Block 6 (i.e., random block in the learning phase).

The SRTT was presented, and responses recorded, using E-Prime 2.0 software. Both accuracy and reaction times were recorded as participants completed the Learning and Retention phase of the task. Trials in which participants did not make a response were coded as incorrect. For each participant, the mean RT for each block was computed. These data were used to examine learning and retention of the FOC and SOC sequences.

In the SRTT literature, RT are the main dependent variable of interest, however, accuracy data were analyzed to ensure participants were correctly responding to the visual stimulus. Table 1 presents the mean proportion of correct responses reported by FOC/SOC learning group and Nap/Wake session. This table shows that accuracy approached ceiling for both groups (i.e., FOC and SOC groups), and test sessions (i.e., Nap, Wake session). To formally test for differences in accuracy, the proportion of correct responses were submitted to a 2 (Group: FOC, SOC) × 2 (Session: Nap, Wake) × 9 (Block: Block 1–9) Mixed Design Factorial ANOVA. To correct for non-normality an arcsine transformation was applied to the data. Non-significant differences and small effect sizes were observed for the main effects of Group [F_{(1, 38)} = 0.652, p = 0.425, η_p² = 0.017] and Session [F_{(1, 38)} = 0.761, p = 0.389, η_p² = 0.020] on accuracy. A significant effect of Block on accuracy was observed [F_{(8, 304)} = 10.773, p < 0.001, η_p² = 0.221]. The main effect of Block can be attributed to accuracy being slightly lower in Block 6 relative to the other blocks (see Supplementary Material Analysis for pairwise comparisons of means). All interaction terms were non-significant and associated with small effect sizes {Group × Session: [F_{(1, 38)} = 0.102, p = 0.751, η_p² = 0.003]; Group × Block: [F_{(1, 38)} = 0.996, p = 0.439, η_p² = 0.026]; Group × Session × Block: [F_{(1, 38)} = 0.176, p = 0.994, η_p² = 0.005]}. These analyses indicate that, overall, there was no evidence to suggest a difference in accuracy between the FOC/SOC Groups and Nap/Wake Sessions.

Proportion of correct responses on the SRTT reported by FOC/SOC sequence learning groups and nap/wake conditions.