Neurons in the primate visual cortex (area V1) are tuned for spatial frequency based on their position in the visual field. Several studies used functional magnetic resonance imaging (fMRI) to investigate the dependency, reporting preferred spatial frequencies (tuning curve peaks) of V1 voxels as a function of eccentricity, but their results differ by up to two octaves, owing to differences in stimuli, measurements, and analysis methodology. For a study, researchers investigated spatial frequency tuning inside the human primary visual cortex at a millimeter precision across stimulus orientation and visual field locations.
They investigated fMRI responses to a unique set of stimuli, which were built as sinusoidal gratings in log-polar coordinates and had a circular, radial, and spiral geometries. The local spatial frequency of each individual stimulus changes inversely with eccentricity, and the whole collection of stimuli spans a wide range of spatial frequencies and orientations at any given point in the visual field. The preferred spatial frequency is well-fit by a function that changes as the inverse of the eccentricity plus a tiny constant across the measured range of eccentricities.
They also discovered tiny but consistent effects of local stimulus orientation, measured in absolute and relative to visual field position. Peak spatial frequency is higher for pinwheel stimuli than annular stimuli, and for horizontal stimuli than vertical stimuli.
Reference:jov.arvojournals.org/article.aspx?articleid=2778653
