The Simon effect towards memorized locations: EEG support for the involvement of attention

About a decade ago it was shown that the Simon effect, the tendency to react towards the side of a stimulus when its location is irrelevant, also occurs when stimuli have to be retrieved from memory. Recently, it was proposed that spatial attention may be responsible for this effect as it might select the relevant object in spatial working memory. An experiment employing the electroencephalogram (EEG) was carried out in which a colored frame (blue, yellow, green, or red) indicated what colored stimulus, one out of four presented in separate quadrants, was the target. The frame occurred either before, simultaneously with, or after the stimuli. In the latter case, the stimuli were first masked and were no longer visible, implying that they had to be retrieved from memory. Simon effects were observed in all conditions, implying that responses were also faster when the side of the to-be-memorized stimulus and the required response side corresponded. Importantly, determination of a newly derived EEG measure, the lateralized power spectra (LPS) in this condition revealed increased ipsilateral occipitoparietal power at around 500 ms after frame onset in the alpha band, supporting the view that attention was directed towards the location of the to-be-memorized item.