Disentangling temporal integration and segregation in multiple object individuation

Object individuation, the process of endowing visual elements with objecthood, is known to have a limited capacity, as demonstrated by the subitizing phenomenon-the rapid and precise enumeration of small quantities (up to three or four items). Previous research has primarily focused on multiple object individuation when components defining each object are presented simultaneously. However, the impact of temporal factors remains understudied. This study investigates the role of temporal processing modes in subitizing. Specifically, we investigated whether subitizing remains feasible and maintains a comparable capacity when object-defining components are presented at different times and need to be either combined into a single object (temporal integration) or separated into distinct objects (temporal segregation). Across two experiments using paradigms based on the missing/odd element task, the impact of different temporal operations (integration vs. segregation) on subitizing was examined after task difficulty was equalized by individually-adjusted inter-stimulus intervals. The results revealed that subitizing is a ubiquitous phenomenon even when target components are presented at different times. Critically, whether these components are temporally integrable or separable influences subitizing capacity. Temporal segregation exhibited a higher subitizing capacity and lower cognitive resource demands than temporal integration, likely because it prioritizes perceptual sensitivity to change over maintaining perceptual continuity and stability during the initial stage of object individuation. Additionally, temporal integration-based subitizing benefits more from an increased repetition of displays than temporal segregation-based subitizing. These findings demonstrate that task-dependent temporal processing modes modulate the efficiency and capacity of numerical individuation, underscoring the importance of temporal organization in multiple object individuation.