Procedure and task
After subjects were familiarized with the MEG chamber, a written
informed consent was given and signed. Then, subjects were seated in the
shielded room placing their head under the MEG helmet. The experiment
consisted of a speeded detection paradigm similar to the experiment
published by Gundlach et al. (2020). In general, a spatial cueing design
with a pre-cue baseline task was utilized. Before a spatial cue
indicated which visual hemifield had to be attended, participants
performed a detection task. Thereby, the volunteers had to focus onto
the central fixation cross in order to detect small size changes of the
cross or extend spatial attention to the peripheral rings to detect
segments of luminance changes within the rings at both visual hemifields
simultaneously. The central fixation and peripheral rings conditions
were assigned to two blocks of 240 trials each. Half of the participants
started with the central fixation condition and then were administered
the task that required attending the peripheral rings. The other half of
the volunteers executed the tasks in reverse order. Each block contained
60 target, 60 distractor and 120 trials without any changes (no events).
Targets and distractors for both pre-cue tasks were presented randomly
within a time interval between 300 ms after trial onset and 500 ms
before the presentation of the post-cue task (see below).
The pre-cue task duration varied randomly between 1500 ms to 2000 ms.
Then, the fixation cross changed its color either to red or blue
indicating that the left or right visual hemifield had to be attended,
respectively. The assignment of the color and hemifield was
counter-balanced across participants. During the post-cue time interval,
ranging from 3000 ms to 3500 ms, participants had to detect luminance
decreases of a small segment of one of the peripheral rings (as in the
pre-cue task). However, targets were only luminance changes in the
to-be-attended visual hemifield. Luminance changes in segments of the
ring in the to-be-ignored visual hemifield were considered as
distractors. During the post-cue interval one, two or no events could
occur. The events (targets or distractors) were presented between 300 ms
after the post-cue and 500 ms before the trial end but were separated by
at least 800 ms if two events occurred. The participants had to indicate
the detection of a target in pre- and post-cue trials with a button
press of the right index finger (half of the participants had to use the
left index finger). The combinations of pre-cue (attend fixation cross
vs. attend peripheral rings) and post-cue tasks (attend left vs. right
visual hemifield) were fully balanced and each condition was repeated
120 times resulting in 480 trials in total. The experiment started with
12 practice trials (6 pre-cue fixation and 6 pre-cue peripheral rings
trials).