Flexibility and Invariance of Object Representations in the Human Brain.

The human brain represents objects in a way that is both invariant across instances and flexible enough to support different contexts and tasks. Yet how the brain reconciles these demands, holding an objecťs representation stable while flexibly reshaping it to meet the current context, remains unknown. Using fMRI during naturalistic movie viewing we investigated how the same objects are represented when they are passive scene elements versus targets of goal-directed actions. Action targets engaged a parietal action network centered in the supramarginal and postcentral gyri, while passive objects recruited a distributed occipito-temporal network involved in visual object recognition. Within context-selective networks, representational geometry showed a double dissociation: target objects were organized by action affordance and hand posture affordance dimensions, while passive objects aligned with semantic dimensions. The visual structure of object representations, by contrast, was invariant across contexts. Searchlight analyses further showed that this dissociation reflected the relative engagement of networks of regions rather than the strict presence or absence of each representational format. Flexibility and invariance are not opposing principles of neural representation, but operate simultaneously at different levels of a common, distributed representational system.