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

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

Congreso; Latin American Brain Mapping Network (LABMAN); 2017

Latin American Brain Mapping Network (LABMAN) - Organization for Human Brain Mapping

Daily task involves the repetition of a sequence of steps to achieve a certain goal. For instance, if we are looking for an old friend in this conference, we have to inspect several faces before finding them. The individual processing of information from an visual stimulus within the search has been extensively studied. However, how these individual responses are embedded in a more complex behavior have been left relatively aside. Some M/EEG and monkey experiments have shown gradual changes associated with the accumulation of information or expectation, both in the amplitude or spectral profiles in different brain areas. In parallel, recent co-registration of EEG and eye movements experiments have been used to study local brain dynamics related to individual fixations (fixation-Related Potentials; fERPs), but their progression throughout the task have been largely ignored. In this study, we aim to extend previous results on visual search and further investigate the dynamics of brain potentials throughout the sequence of fixations.We performed an EEG and eye movements co-registration experiment in which participants searched for a target face within natural images of crowds. FERPs showed target detection effects with a spatio-temporal localization consistent with previous works. Moreover, we found a significant modulation of the target-related component with the trial length. Interestingly, when inspecting the global dynamics of distractor processing within a trial, we observed a gradual change of the fERP?s baseline amplitude with the fixation rank. These global dynamics was also reflected in the spectral profile, as the power in the fronto-central alpha band decreased along the search, while the power in occipital theta band increased. This suggests a growing engagement in the search, in terms of 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.