Abstract
The neural underpinnings of face processing have largely been investigated under fixed-gaze. The electrophysiological hallmark of face processing is the N170 component, which emerges in the occipitotemporal cortex around 170 ms after stimulus onset and is characterized by a larger amplitude in response to pictures of faces, compared to other object categories. Several properties modulating this component have been extensively studied, including its sensitivity to face inversion and low-level manipulations (see, e.g. Rossion, 2015). However, little is known about face processing in natural viewing. A recent study (Kamienkowski, Varatharajah, Sigman & Ison, 2018) reported strong fixation-related potentials (fERPs) to faces in a free-viewing visual search task and a significant difference between target and distractor faces around 170 ms after fixation.
In this study, we co-registered EEG and eye tracking to investigate fERPs to pictures of faces and objects during visual search and free exploration. Participants were asked to search for one target face or object stimulus during visual search blocks (VS) and to explore an array of faces and objects embedded in random noise during free exploration (EXP). We hypothesized that a larger N170 would be elicited by fixations to faces in comparison to objects. Importantly, based on a recently proposed framework (Kamienkowski et al., 2018), we also hypothesized that the early target detection that has previously been reported largely reflects saccade inhibition, and would therefore be activated differently for easy distractors (different categories) than hard distractors (same category). Preliminary analyses of the fERPs show robust early potentials, but no differential activation for different categories. Possible interpretations in terms of differences in low-level features, reduced signal to noise ratio and superposition of brain potentials are discussed.