ERP evidence for temporal independence of set size and object updating in object substitution masking

Christine M. Salahub, Stephen M. Emrich

To keep track of dynamically changing objects in one's environment, it is necessary to individuate them from other objects, both temporally and spatially. Spatially, objects can be selected from nearby distractors using selective attention. Temporally, object updating processes incorporate new information into existing representations over time. Both of these processes have been implicated in a type of visual masking called object-substitution masking (OSM). Previous studies have found that the number of distractors (impacting selective attention) interacts with the strength of OSM. However, it has been suggested that this interaction is an artifact of ceiling performance at low set sizes, rather than necessitating a failure of attention during masking. Using event-related potentials (ERPs), we examined whether set size and masking interact as measured by markers of selective attention (N2pc) and visual working memory consolidation/maintenance (SPCN). Set size was found to affect the N2pc (200-350 ms) and late SPCN (500-650 ms), reflecting increased demands on selective attention and unnecessary storage respectively. An early window of the SPCN (350-500 ms) was affected by masking, suggesting that OSM influences object consolidation processes in this window, independent of the number of distractors. Overall, it was found that selective attention and visual awareness are dissociable neural processes in OSM, and that they are independently affected by set size and masking manipulations. Moreover, we found that the early SPCN may reflect disruptions to object consolidation, potentially revealing a neural mechanism supporting an object individuation-through-updating account of OSM.