2.1 Participants
For the determination of the sample size, the G*Power 3.1.9.7 software (Faul et al., 2009) was used. A priori power analysis was used to obtain a minimum power of 0.90, as effect size was selected f=0.338 taken from the minimum partial eta squared of Bianco et al. (2020) results, which used a similar ERP design. The other settings were the following: α=0.05, number of measurements=6, correlation among repeated measures=0.50 and, non-sphericity correction ε=1. This calculation resulted in a recommended minimum sample size of 19 for within-factors repeated measures analyses of variance (ANOVA) used for ERP analyses. After these calculations, 19 volunteers participated in the study (mean age 23.2 years ±1.3, 5 females, 14 males). As inclusion criteria, all participants were healthy having no history of neurological, psychiatric, or chronic somatic problems. The participants did not take medication during the experimental sessions and had normal or corrected-to-normal vision. All participants were right-handed. Before the intervention, each participant was informed about all procedures and was asked to sign an informed consent. The procedures followed the Declaration of Helsinki guidelines and were approved by the committee for the authorization of the research (CAR) at the University of Rome “Foro Italico”.
2.2 Stimuli and procedure
The experiment was done in the Cognition and Action Neuroscience Laboratory at the University of Rome “Foro Italico”. Participants were tested in a low-lit, sound-attenuated room after an electroencephalographic (EEG) cap was mounted on the scalp. They were placed in front of a computer screen at 170 cm from their eyes.
Participants performed during the EEG recording a discriminative response task (DRT), i.e., a Go/No-go paradigm. A yellow fixation point (diameter 0.15°) on a black background was present in the center of the screen throughout the whole experimental session. Four visual stimuli (i.e., square configurations subtending a side of 4° and consisting of vertical and/or horizontal bars) were randomly visualized for 250 ms with equal probability; the stimulus–onset asynchrony varied from 2200 to 3200 ms to prevent stimulus prediction and ERP overlaps with previous and following stimuli. Participants had to press the button with the right index finger as soon as possible only when (two out of four) designed ‘Target’ stimuli (Go) appeared on the screen, while they had to withhold the motor response if the when ‘Non-target’ stimuli (No-go) appeared; the experimenter equally emphasized speed and precision. Figure 1 shows a schematic representation of the stimuli and the timing. The order of presentation of the four stimuli was randomized between runs. The duration of each run was 2 m and 15 s with a pause interleaved. Ten runs for three conditions were administered allowing to collect 400 trials for each stimulus category in approximately 70 m, depending on the individual rest time during pauses.