View-invariant representations in ancestral cortex

A multilayered, thalamorecipient visual cortex emerged ~320 million years ago in stem amniotes. Despite its importance for understanding the evolution of cortical computation, its function remains unknown. We recorded visually evoked responses in the dorsal cortex of behaving turtles, considered a mammalian neocortex homolog. Using a spatial oddball paradigm, we found tuning to stimuli in deviant positions alongside adaptation to standard positions within the visual field. Eye tracking demonstrated that responses remained spatially selective despite gaze shifts altering retinal stimulus position. Thus, the turtle cortex encodes unexpected visual stimuli using computations invariant to retinal position, a property previously observed only in higher mammalian cortices. These results indicate that invariance computations preceded the evolution of local filtering computations in mammalian primary cortices, pointing to a previously unidentified function for ancestral cortices. They also challenge hierarchical models of invariance computations, which assume that invariance is built from low-level features across multiple processing steps.