The process of object individuation shared across visual and tactile modalities.

Distinguishing objects from the background, a process known as Object Individuation (OI), is fundamental for us to interact with the environment and relies critically on location information across sensory modalities. Nonetheless, it remains unclear and contested in the literature whether the enumeration of tactile and visual events relies on the OI process (especially given spatial constraints), or if the representation of numerosity is governed by a modality-independent mechanism common to both visual and tactile systems. In this study, we used a cross-modal enumeration and a working memory dual-task paradigm to investigate whether OI processes in tactile and visual modalities draw upon a shared cognitive resource. We implemented two experiments. In Experiment 1, we combined a tactile working memory (WM) task with visual enumeration, and in Experiment 2, we used a visual WM task with tactile enumeration. Both experiments revealed that the task-irrelevant WM load significantly modulated subitizing performance (enumeration of small quantities) in the target modality. Under high WM load, participants showed increased error rates and reduced subitizing capacity compared to low load. This modulation is selective to the subitizing range and cannot be attributed to general dual-task costs, ruling out general dual-tasking effects. The data shows that visual and tactile working memory and enumeration ("subitizing") share a common OI process that operates on location, independent of the sensory modality. This finding is consistent with existent neuroimaging evidence that highlights the modality-shared role of frontoparietal brain regions (e.g., IPS, LPFC) in enumeration and working memory.