Active search signatures in a free-viewing task exploiting concurrent EEG and eye movements recordings

Abstract

AbstractEarly access to categorical visual information plays an important role in real-world behaviour. Under fixed-gaze conditions, there are well-established electrophysiological signatures of categorical processing like the N170 EEG component. Here we aimed to study how the sensitivity to category information extends to a free viewing paradigm and consider how ecologically-relevant variables such as the particular task performed influence the brain activity. We co-registered EEG and eye-tracking to investigate fixation-related potentials to pictures of different categories during visual search and exploration. Participants were asked to “observe” / “search for one target from” an array of faces and objects embedded in random noise. We applied a deconvolution analysis approach to estimate the contribution of the different elements embedded in the task. Consistent with classical fixed-gaze experiments and a handful of free viewing studies, we found a robust categorial effect in occipital and occipitotemporal electrodes. We also report a task effect, which was reflected by a negative occipital activation and a positive frontal activation of the estimates. To further investigate the dynamics along the trial, we defined a trial progression score and found significant effects of trial progression, and the interaction between the trial progression and task effects. Overall, these results generalise the characterisation of early visual face processing to a wider range of experiments and show how a suitable analysis approach allows to discern among multiple neural contributions to the signal, preserving key attributes of real-world tasks.