Fixation related Visual Mismatch Negativity in Free Viewing

Background: Accumulating evidence shows that vision in natural conditions could be studied by combining EEG and eye tracking and using saccades as triggers for the event onset of the Fixation-Related Potentials (FRPs) and the Oculomotor Inhibition (OMI) that follows every saccade. The result of this analysis was suggested to be equivalent to flashed stimuli with prior parafoveal preview. Previous studies that measured the response to visual deviants in a sequence of flashed stimuli found increased negativity of the occipital N1 component (visual Mismatch Negativity, vMMN), and prolonged saccadic inhibition for the unexpected. The first aim of the current study was to develop an oddball paradigm in free viewing and investigate whether a similar mismatch ERP and prolonged OMI for deviance could be found. The second aim was to study the interplay between these two measures, oculomotor dynamics and neurophysiology. Methods: We developed a visual oddball paradigm on a static display to generate expectancy and surprise across successive saccades. Observers inspected items in specific positions one after the other for 5 seconds per trial. The small patterns E and inverted E were arranged on the screen along a horizontal path with one rare (oddball) and one frequent (standard). Results: Our results show significantly larger FRP of the occipital N1 for the mismatched E compared with the standards and prolonged OMI of the following saccade or microsaccade as previously found for transient oddballs. Moreover, the latency of the following saccade was positively correlated with the N1 magnitude in all trials including oddball and standards. Conclusions: Our results show for the first-time prolonged OMI and stronger fixation-related N1 to a visual mismatch (vMMN) in free, but task-guided viewing. These two signals combined could serve as markers of prediction error in free viewing.