Figure 1. Schematic illustration of a trial sequence.

Each trial (here: high perceptual load condition) started with a cue (1000–1500 ms) that indicated the two symbols, which had to be detected within the symbol stream. Low perceptual load required subjects to respond to the blue color of these symbols, high perceptual load involved a discrimination task (respond when one symbol is printed in red or the other symbol is printed in green). Symbols were presented at a stimulation frequency of 8.5 Hz while the underlying IAPS picture was flickering simultaneously at 12 Hz. Stimulation started with the scrambled version of the IAPS picture (see Methods for scrambling procedure) that changed between 700–1517 ms to normal view of either a neutral or an unpleasant image (here: unpleasant). Inter-trial intervals lasted 700 ms and a fixation cross was present throughout the experiment.