A cortical hierarchy of sensory representations from physical structure to idiosyncratic perception

Perception begins with the physical structure of the external world, yet each of us remaps that structure into an idiosyncratic ordering shaped by individual experience and makeup. To ask how these two orderings are reflected in the brain, we used fMRI in 47 participants to measure the representation of olfactory and visual stimuli chosen such that similarities among the odorants mirrored those among the images. Olfactory and visual cortices each reflected physical similarity more strongly than idiosyncratic perceptual similarity. By contrast, a whole-brain search for the alternative uncovered the left angular gyrus, which reflected idiosyncratic perceptual similarity in both olfaction and vision. Connectivity analysis depicted this region as a likely hub for such representation, and dynamic causal modeling supported this observation. These findings reveal a transition from stimulus-centered representations in modality-specific sensory cortex to a modality-general observer-centered representation in the angular gyrus, suggesting a potentially fundamental hierarchy in brain organization.