Experiment 1, behavioral results.a, Box plots of reaction time (RT) from correct trials and accuracy in post-stimulation memory blocks show older adults were slower (t82 = 2.331, p = 0.022, dz = 0.509) and less accurate (t82 = 5.587, p < 0.01, dz = 1.219) at baseline, relative to younger adults. After stimulation, accuracy improved (t41 = 3.738, p = 0.001, dz = 0.577), removing the difference between groups (t82 = 0.939, p = 0.350, dz = 0.205). RT did not differ between conditions (t41 = 0.641, p = 0.527, dz = 0.099). Box plots of accuracy (b) and RT (c) from memory blocks sorted into 9 sequential bins (4 minutes per bin with 4 minutes between each bin from interleaved control blocks) shows significant group differences at every time bin for accuracy (ts82 > 6.824, ps < 0.01, dsz > 1.489) and RT (ts82 > 2.432, ps < 0.018, dsz > 0.531), at baseline. Stimulation improved accuracy at every time bin (ts41 > 4.393, ps < 0.01, dsz > 0.678), relative to sham, except the first (t41 = 0.986, p = 0.330, dz = 0.152). Stimulation briefly sped RT at time bins 3 (t41 = 2.841, p = 0.007, dz = 0.438), 4 (t41 = 2.278, p = 0.028, dz = 0.352), and 6 (t41 = 2.282, p = 0.028, dz = 0.352). Between-group comparisons used independent samples two-tailed t-tests (n = 84). Within-group comparisons used paired sample two-tailed t-tests (n = 42). Box-plot center, median; box limits, lower and upper quartiles; whiskers, lower and upper extreme values. * p < 0.05. ** p < 0.01.
