Masks are memorable: ERP evidence on visual short-term memory and individuation in object substitution masking

Abstract

ABSTRACT Object substitution masking (OSM) involves reduced perceptibility by a briefly lingering mask despite no spatial target-mask overlap. Two primary accounts for this phenomenon posit differences in object representation in visual short-term memory (VSTM). In the object substitution account a single representation resides in VSTM: a lone mask when attention is not focused on the target, and a lone target+mask when attention is focused on the target. The object updating account assumes individualization, with mask-alone and target+mask representations concurrently present in VSTM in correct delayed-offset OSM trials. We explored object individuation in OSM, focusing on the quantity of representations in VSTM in two OSM tasks with low (Easy Search) and high (Difficult Search) attentional demands, using event-related potentials (ERPs). Individuation was indicated in correct trials, with ERPs showing greater negativity in the sustained posterior contralateral negativity (SPCN) component for delayed compared to co-terminating offset conditions, consistent with greater VSTM load in delayed-offset. This effect, indicating target+mask and mask-alone as distinct memory representations, was found in Easy Search only. Additionally, no SPCN difference was found between correct and incorrect delayed trials in Difficult Search. We discuss our results in the context of individuation and perceptual load in OSM.