Gradual change of cortical representations with growing visual expertise for synthetic shapes.

Visual expertise for particular categories of objects (e.g., birds, mushrooms, minerals, and so on) is known to enhance cortical responses in parts of the ventral occipitotemporal cortex. How is such additional expertise integrated into the prior cortical representation of life-long cumulative visual experience? To address this question, we record multivariate BOLD responses to synthetic visual objects and track changes in pairwise distance as initially unfamiliar objects gradually become familiar ( representational similarity analysis, RSA). We find view-independent responses to synthetic shapes (i.e., an invariant representation) in large parts of the ventral occipitotemporal cortex, including the primary visual cortex. Surprisingly, the quality of representation is already high even when shapes are still unfamiliar. As shapes become familiar with repeated viewing, this quality remains high, but representational geometry shifts with more experience. For visually similar shapes that are not repeated and therefore remain unfamiliar, the representation degrades and becomes progressively marginalized. We conclude that, at least for highly dissimilar synthetic shapes, functional imaging responses can reveal detailed representational geometry at the level of exemplars, as well as gradual changes in this geometry due to experience and learning.