Our remarkable ability to process complex visual scenes is supported by a network of scene-selective cortical regions. In spite of growing knowledge about the scene representation in these regions, much less is known about the temporal dynamics with which these representations emerge. We conducted two experiments aimed at identifying and characterizing the earliest markers of scene-specific processing. In the first experiment, human participants viewed images of scenes, faces, and everyday objects while Event Related Potentials (ERPs) were recorded. We found that the first ERP component to evince a significantly stronger response to scenes than the other categories was the P2, peaking approximately 220ms post-stimulus onset. To establish that the P2 component reflects scene-specific processing, in the second experiment, we recorded ERPs while the participants viewed diverse real-world scenes spanning three global scene properties: spatial expanse (open/closed), relative distance (near/far), and naturalness (manmade/natural). We found that P2 amplitude was sensitive to these scene properties at both the categorical level, distinguishing between open and closed natural scenes, as well as at the single image level, reflecting both computationally derived scene statistics and behavioral ratings of naturalness and spatial expanse. Together, these results establish the P2 as an ERP marker for scene processing, and demonstrate that scene-specific global information is available in the neural response as early as 220ms.
Significance Statement Humans can process complex scenes very rapidly and efficiently. While recent years have shown great progress in understanding where in the brain scene processing occurs, it is still unknown when in the brain scene-specific processing occurs. We describe a novel electrophysiological signature of scene-selective processing, the P2 event-related-potential (ERP) component. We found that P2, which peaks around 220ms post-stimulus onset shows a greater response to scenes than other categories, and distinguishes between scene images based on their global diagnostic properties, such as naturalness and spatial layout. Our findings, therefore, provide critical insight about the time course of scene processing, as they demonstrate that diagnostic scene information can be found as early as 220 ms after stimulus onset.
Conflict of Interest: Authors report no conflict of interest.
Funding sources: This work has been supported by the Intramural Program of the National Institute of Mental Health (ZIAMH002909)