We calculated the needed sample size using G*Power 3.1 software [66 (link)]. Experiment 1 investigated whether anti-phase alpha-tACS and in-phase alpha-tACS would induce different behavioral and electrophysiological effects. Based on the medium or large effect sizes reported in previous studies that used NIBS to modulate parietal alpha oscillations and WM [48 (link),50 (link)], a medium effect size (Cohen’s d = 0.5) was assumed. Thus, a sample size of 34 participants was needed to detect a reliable effect with a statistical power of 80% and an alpha probability of 0.05 in a two-tailed paired t-test.
A total of 48 healthy participants between the ages of 18 and 40 completed Experiment 1. All participants were right-handed and reported no metal implants in the brain, no implanted electronic devices, no history of neurological problems or head injury, no current use of psychoactive medication, no history of craniotomy, and no skin sensitivity; the participants were nonpregnant, had normal or corrected-to-normal visual acuity, and were not enrolled in any other NIBS research within 3 months of their study participation. Participants who failed to follow directions or did not understand instructions were removed from the study. All participants were recruited in Hefei, China through advertisements or posters. Eight participants were excluded from the analyses due to poor EEG signals or malfunctions of the tACS stimulator to trigger the intended electrical stimulation. One participant whose alpha activity was too weak for detection and who therefore had to repeat the Baseline Sternberg task 3 times per session was also excluded. The remaining 39 participants (19 females, mean age ± SD:21.1 ± 2.2 years, mean education ± SD:14.7 ± 1.8 years) were included for behavioral and EEG analyses, which meets the sample size requirement.
A total of 48 healthy participants between the ages of 18 and 40 completed Experiment 1. All participants were right-handed and reported no metal implants in the brain, no implanted electronic devices, no history of neurological problems or head injury, no current use of psychoactive medication, no history of craniotomy, and no skin sensitivity; the participants were nonpregnant, had normal or corrected-to-normal visual acuity, and were not enrolled in any other NIBS research within 3 months of their study participation. Participants who failed to follow directions or did not understand instructions were removed from the study. All participants were recruited in Hefei, China through advertisements or posters. Eight participants were excluded from the analyses due to poor EEG signals or malfunctions of the tACS stimulator to trigger the intended electrical stimulation. One participant whose alpha activity was too weak for detection and who therefore had to repeat the Baseline Sternberg task 3 times per session was also excluded. The remaining 39 participants (19 females, mean age ± SD:21.1 ± 2.2 years, mean education ± SD:14.7 ± 1.8 years) were included for behavioral and EEG analyses, which meets the sample size requirement.
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