Stimulus orientation in the primary visual cortex of primates and carnivores is mapped as iso-orientation domains radiating from pinwheel centres, where orientation preferences of neighbouring cells change circularly. Whether this orientation map has a function is currently debated, because many mammals, such as rodents, do not have such maps. Here we show that two fundamental properties of visual cortical responses, contrast saturation and cross-orientation suppression, are stronger within cat iso-orientation domains than at pinwheel centres. These differences develop when excitation (not normalization) from neighbouring oriented neurons is applied to different cortical orientation domains and then balanced by inhibition from un-oriented neurons. The functions of the pinwheel mosaic emerge from these local intra-cortical computations: Narrower tuning, greater cross-orientation suppression and higher contrast gain of iso-orientation cells facilitate extraction of object contours from images, whereas broader tuning, greater linearity and less suppression of pinwheel cells generate selectivity for surface patterns and textures.

Pose estimation of objects in real scenes is critically important for biological and machine visual systems, but little is known of how humans infer 3D poses from 2D retinal images. We show unexpectedly remarkable agreement in the 3D poses different observers estimate from pictures. We further show that all observers apply the same inferential rule from all viewpoints, utilizing the geometrically derived back-transform from retinal images to actual 3D scenes. Pose estimations are altered by a fronto-parallel bias, and by image distortions that appear to tilt the ground plane. We used pictures of single sticks or pairs of joined sticks taken from different camera angles. Observers viewed these from five directions, and matched the perceived pose of each stick by rotating an arrow on a horizontal touchscreen. The projection of each 3D stick to the 2D picture, and then onto the retina, is described by an invertible trigonometric expression. The inverted expression yields the back-projection for each object pose, camera elevation, and observer viewpoint. We show that a model that uses the back-projection, modulated by just two free parameters, explains 560 pose estimates per observer. By considering changes in retinal image orientations due to position and elevation of limbs, the model also explains perceived limb poses in a complex scene of two bodies lying on the ground. The inferential rules simply explain both perceptual invariance and dramatic distortions in poses of real and pictured objects, and show the benefits of incorporating projective geometry of light into mental inferences about 3D scenes.

The cerebral cortex receives multiple afferents from the thalamus that segregate by stimulus modality forming cortical maps for each sense. In vision, the primary visual cortex maps the multiple dimensions of the visual stimulus in patterns that vary across species for reasons unknown. Here we introduce a general theory of cortical map formation, which proposes that map diversity emerges from species variations in the thalamic afferent density sampling sensory space. In the theory, increasing afferent sampling density enlarges the cortical domains representing the same visual point, allowing the segregation of afferents and cortical targets by multiple stimulus dimensions. We illustrate the theory with an afferent-density model that accurately replicates the maps of different species through afferent segregation followed by thalamocortical convergence pruned by visual experience. Because thalamocortical pathways use similar mechanisms for axon segregation and pruning, the theory may extend to other sensory areas of the mammalian brain.