Tactile Object Individuation on a fingertip is Associated with Neural Representations in the Bilateral Inferior Parietal Lobule

Object individuation (OI) is the spatial segregation of target stimuli from their background, a process essential for environmental interaction. Leveraging location cues, the perceptual system can individuate approximately four objects (the ‘OI range’); this capacity limit serves as a primary bottleneck for related cognitive tasks, including visual working memory and subitizing (the rapid enumeration of small sets). While visual OI is extensively characterized, its counterpart in the tactile modality remains under-investigated. Using fMRI, we localized the task-independent tactile OI substrate to the bilateral inferior parietal lobule (IPL), with broader frontoparietal recruitment observed during enumeration. Within the OI range, IPL voxel patterns successfully decoded both numerosity and working memory loads across tasks. This task-invariant, quantity-specific activity confirms the IPL’s role in tactile OI. Crucially, decoding was restricted to the OI range, reflecting the core capacity limits of the perceptual system. These findings establish the bilateral IPL as a task-invariant neural substrate for tactile OI, and are consistent with prior visual evidence suggesting a central role of the fronto-parietal network in OI. By demonstrating shared resources between tactile subitizing and working memory, our study extends the fronto-parietal account of object individuation to the tactile modality and provides a foundation for future investigations of potential cross-modal commonalities in OI mechanisms.