200 Chapter 7 Figure 1. The modified sustained attention to response task paradigm. In baseline blocks, participants did not have to respond (No-Go). In the moderate and higher difficulty level participants had to responded by button press to all digits (Go) except for the digit “3” (No-Go). The difficulty levels differed in duration of stimulus presentation (250 ms in moderate difficulty level and 100 ms in higher difficulty level). The SART error scores were calculated separately for the two difficulty levels and compared between the groups as a measure of task performance. Mean reaction times (RTs) were determined per difficulty level relative to stimulus onset and compared between the groups. Additional mean error rates were calculated per difficulty level per repetition to assess the behavioural time-ontask effect over the entire SART. Mean scores were also computed separately for the early half and late half of each difficulty level to identify possible withinblock time-on-task differences. Image acquisition A high-field 3T Philips Achieva MRI scanner (Philips Healthcare, Best, The Netherlands) was used for MRI data acquisition with a 32-channel head coil and sponge cushions to minimize head movements. For functional MRI scans, whole-brain functional T2*-weighted MRI data were acquired using a gradient-echo planar imaging (EPI) sequence (38 slices with a 0.25 mm gap; repetition time (TR) = 2250 ms; echo time (TE) = 29.94 ms; field of view (FOV) 200 × 200 × 104.25 mm; matrix size 80 × 80; flip angle = 80°; 2.5 × 2.5 × 2.5 mm3 voxel size). For coregistration purposes, we also acquired T1-weighted
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