Face Familiarity Revealed by Fixational Eye Movements and Fixation-Related Potentials in Free Viewing

Event-related potentials (ERPs) and the oculomotor inhibition (OMI) in response to transient visual stimuli are known to be sensitive to different stimulus properties, including attention and expectation. In natural vision, transient stimulation of the visual cortex is generated primarily by saccades. Recent studies suggest that the core EEG components in free viewing, induced by saccades (fixation-related potentials, RPs), are similar to the ERP components with flashed stimuli. We have recently found that the OMI in response to flashed stimuli is sensitive to face familiarity. Here, we investigated whether fixation-related-potentials (FRPs) and microsaccade inhibition (OMI) in free viewing are sensitive to face familiarity. Observers (N=15) freely watched a slideshow of seven unfamiliar and one familiar world leaders facial images presented randomly for 4-seconds periods, with multiple images per identity. We measured the occipital fixation-related N1 relative to the P1 magnitude as well as the associated fixation-triggered OMI. We found that the average N1 was significantly smaller and the OMI was shorter for the familiar face, compared with any of the 7 unfamiliar faces. Moreover, the P1 was suppressed across saccades for the familiar but not for the unfamiliar faces. Overall, the results indicate that the occipital FRP and the OMI in free viewing are sensitive to face familiarity; this could perhaps be used as a novel physiological measure for studying hidden suppressed memories.