Representing Visual Objects, Attention, and Load in Human Occipito-temporal and Posterior Parietal Cortices

Stability and adaptability are two essential components of everyday vision, enabling us to maintain an object's identity as we attend to different features under varying task loads. We hypothesize that these two components of vision are supported by the interactions among object, attention, and load representations, and the interplay between the human occipito-temporal cortex (OTC), given its visual representation invariance, and the posterior parietal cortex (PPC), an adaptive visual processing center. To test this, human participants performed four tasks on the same stream of colored objects with varying attention (attending to color or shape) and load (1-back or 2-back repetition detection). Although the exact neural mechanisms differ in how object, attention, and load modulate neural responses, by placing them as different factors in the same visual representational space using fMRI pattern decoding, we directly compared their effects on visual responses and interactions. We found significant object, attention, and load representations across OTC and PPC, with a gradual transition from more object-sensitive representations in OTC to more attention- and load-sensitive representations in PPC. Notably, object, attention, and load representations showed significant interactions and generalizations across changes with each other in both OTC and PPC. When objects were held constant, attention and load were represented independently of each other, showing their neural separability. Together, the invariant and adaptive nature of object, attention, and load representations in OTC and PPC provides both stability in visual processing and adaptation to the ever-changing visual input and task demands.