Time course of brain activity during unrestricted visual search: Co-registering EEG and Eye Movements

KAMIENKOWSKI JE; VARATHARAJAH A; SIGMAN M; QUIAN QUIROGA R; ISON MJ

Wuppertal

Congreso; 19th European Conference on Eye Movements; 2017

When looking for a friend in this conference, we have to inspect several faces before achieving our goal. The processing of visual stimuli within each fixation has been explored in recent EEG and eye movements co-registration experiments (fixation-Related Potentials; fERPs). However, how these individual responses are embedded in more complex behavior has been left relatively aside. Previous experiments with artificial foveated stimuli have shown gradual changes associated with the accumulation of information or expectation, either in the amplitude or the spectral profiles of the EEG signal. This study investigates the brain dynamics throughout the sequence of fixations when searching for a target face within natural images of crowds. FERPs showed target detection effectsconsistent with previous works. Moreover, the target-related component was significantly modulated by the trial length. The global dynamics of distractor processing within a trial showed gradual changes of fERP?s baseline amplitude, as well as major changes in the spectral profile -particularly in the theta and alpha bands-. This can be interpreted in terms of a growing engagement in the search, with changes in expectation and anticipation. Thus, while fixation-related components account for local processing, baseline activity and oscillations provide information about the global progression of the task.