Discrete object representation, attention switching, and task difficulty in the parietal lobe.

An important component of perception, attention, and memory is the structuring of information into subsets ("objects"), which allows some parts to be considered together but kept separate from others. Portions of the posterior parietal lobe respond proportionally to the number of objects in the scope of attention and short-term memory, up to a capacity limit of around four, suggesting they have a role in this important process. This study investigates the relationship of discrete object representation to other parietal functions. Two experiments and two supplementary analyses were conducted to evaluate responsivity in parietal regions to the number of objects, the number of spatial locations, attention switching, and general task difficulty. Using transparent motion, it was found that a posterior and inferior parietal response to multiple objects persists even in the absence of a change in visual extent or the number of spatial locations. In a monitoring task, it was found that attention switching (or task difficulty) and object representation have distinct neural signatures, with the former showing greater recruitment of an anterior and lateral intraparietal sulcus (IPS) region, but the latter in a posterior and lateral region. A dissociation was also seen between selectivity for object load across tasks in the inferior IPS and feature or object-related memory load in the superior IPS.