The timecourse of inter-object contextual facilitation

Abstract

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 ms 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. Significance StatementThis study used electroencephalography decoding to reveal the neural timecourse of inter-object facilitation present for contextually-associated groups of objects (e.g., chair + table). Although ubiquitous in daily life, the object constellation level of representation has rarely been examined compared to isolated objects or entire scenes. By shedding new light on facilitatory interactions between objects, arising before 200ms of visual processing, our results provide insight into the continuum along which objects and scenes exist. At the same time, this work advances the current understanding of the neural basis of real-world size, using strict visual controls to show that inferred information about objects spatial scale in the real world emerges around 200 ms after stimulus onset.