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.