Abstract
Recent work has reported that the first Event-Related Potential (ERP) component to carry scene-selective information is the posterior P2 component (peaking 220ms post-stimulus onset)(Harel et al., 2016). P2 amplitude was higher in response to scenes than to faces and objects and was also sensitive to the global properties of scenes (e.g. naturalness and openness), suggesting that global scene structure is encoded by 220ms of processing. The present study aimed to extend this finding by testing the impact of scene inversion on the P2 component. Inversion is assumed to disrupt global processing, and as such can be used to test the P2 sensitivity to global information, and more generally establish how early stages of scene perception are impacted by inversion. This is especially important as to this date only a handful of studies have examined scene inversion. We recorded ERPs from participants while they passively viewed upright and inverted color images of faces, objects, and scenes. We used 192 individual images in each category, spanning a wide range of category dimensions and properties to prevent the possibility of a salient image property affecting our results. First, we established that the P2 response was indeed scene-selective, with its amplitude higher in response to scenes than faces and objects, replicating Harel et al.’s original study. Second, we found a P2 inversion effect in the form of a reduced P2 amplitude to inverted compared to upright scenes. Earlier visually-evoked components P1 and N1 did not show significant scene inversion effects. Lastly, faces showed the expected N170 inversion effect as well as P1 and P2 inversion effects, while objects showed no inversion effects for any of the early components. Together, these results suggest that global scene processing can be observed at the P2 time window and support the idea that P2 indexes scene-selective neural processing.