The timecourse of inter-object contextual facilitation

High-level vision is frequently studied at the level of either individual objects or whole scenes. An intermediate level of visual organisation that has received less attention is the "object constellation" - a familiar configuration of contextually-associated objects (e.g., plate + spoon). Recent behavioural studies have shown that information from multiple objects can be integrated to support observers' high-level understanding of a "scene" and its constituent objects. Here we used EEG in human participants (both sexes) to test when the visual system integrates information across objects to support recognition, using representations of objects' real-world size as a proxy for recognition. We briefly presented masked object constellations consisting of object silhouettes of either large (e.g., chair + table) or small (e.g., plate + spoon) real-world size, while independently varying retinal size. As a control, observers also viewed each silhouette in isolation. If object context facilitates object recognition, real-world size should be inferred more effectively when the objects appear in their contextually-associated pairs than in isolation, leading to the emergence of real-world size information in multivariate EEG patterns. Representational similarity analysis revealed that neural activity patterns captured information about the real-world size of object constellations from ∼200 msec after stimulus onset. This representation was stronger for, and specific to, object pairs as compared to single objects, and remained significant after regressing out visual similarity models derived from computational models. These results provide evidence for inter-object facilitation of visual processing, leading to a qualitatively different high-level representation of object pairs than single objects.