On sources to variabilities of simple cells in the primary visual cortex: A principled theory for the interaction between geometric image transformations and receptive field responses
The research uses a Gaussian derivative model to show that simple cell receptive fields must be covariant under four geometric transformations: spatial scaling, affine changes, Galilean motion, and temporal scaling. This requires V1 receptive fields to be expanded in shape to allow for matching visual responses across different viewing conditions. This provides a principled link between image geometry and cortical processing structure.