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).