An eye fixation–related potentials analysis of the P300 potential for fixations onto a target object when exploring natural scenes

International audienceThe P300 event-related potential has been extensivelystudied in electroencephalography with classicalparadigms that force observers to not move their eyes.This potential is classically used to infer whether a targetor a task-relevant stimulus was presented. Few researcheshave studied this potential through more ecologicalparadigms where observers were able to move their eyes.In this study, we examined with an ecological paradigmand an adapted methodology the P300 potential using avisual search task that involves eye movements to activelyexplore natural scenes and during which eye movementsand electroencephalographic activity were coregistered.Averaging the electroencephalography signal time-lockedto fixation onsets, a P300 potential was observed forfixations onto the target object but not for other fixationsrecorded for the same visual search or for fixationsrecorded during the free viewing without any task. Ourapproach consists of using control experimentalconditions with similar eye movements to ensure that theP300 potential was attributable to the fact that theobserver gazed at the target rather than to other factorssuch as eye movement pattern (the size of the previoussaccade) or the ‘‘overlap issue’’ between the potentialselicited by two successive fixations. We also proposed tomodel the time overlap issue of the potentials elicited byconsecutive fixations with various durations. Our resultsshow that the P300 potential can be studied in ecologicalsituations without any constraint on the type of visualexploration, with some precautions in the interpretationof results due to the overlap issue