Transformation from a retinal to a cyclopean representation in human visual cortex.

We experience our visual world as seen from a single viewpoint, even though our two eyes receive slightly different images. One role of the visual system is to combine the two retinal images into a single representation of the visual field, sometimes called the cyclopean image [1]. Conventional terminology, i.e. retinotopy, implies that the topographic organization of visual areas is maintained throughout visual cortex [2]. However, following the hypothesis that a transformation occurs from a representation of the two retinal images (retinotopy) to a representation of a single cyclopean image (cyclopotopy), we set out to identify the stage in visual processing at which this transformation occurs in the human brain. Using binocular stimuli, population receptive field mapping (pRF), and ultra-high-field (7 T) fMRI, we find that responses in striate cortex (V1) best reflect stimulus position in the two retinal images. In extrastriate cortex (from V2 to LO), on the other hand, responses better reflect stimulus position in the cyclopean image. These results pinpoint the location of the transformation from a retinal to a cyclopean representation and contribute to an understanding of the transition from sensory to perceptual stimulus space in the human brain.