When Does the Brain Respond to Information During Visual Scanning?

High-stress work environments, such as a flight deck or surveillance systems, provide operators with multiple instruments that have to be monitored constantly using eye movements. Eye tracking allows us to infer when an operator’s overt attention is devoted to an instrument, namely when fixation begins. It is commonly assumed that fixating a visual stimulus equates its processing. In this study, we use an electroencephalogram (EEG) to demonstrate that visual perception, hence processing, can take place even prior to fixation. We show that target onsets give rise to brain responses that are associated with stimulus processing even before targets were fixated. This poses a challenge for the use of the electroencephalogram/event-related potential (EEG/ERP) in visual scanning environments: if fixation onset is not necessarily the onset of perception, it cannot always be used for attributing ERP data.