Orientation dependence of visual hyperacuity contains a component with hexagonal symmetry.

Recently we reported that hyperacuity thresholds for separation-discrimination tasks were not smooth functions of spatial variables but rather were regularly segmented with sharp transitions between the segments. In this study we have measured the orientation dependence of two tasks involving visual hyperacuity, the discrimination of spatial frequencies and the discrimination of vernier offsets, in the vicinity of a transition between segments. The orientation dependence of both tasks contains a periodic component with a period of 60 degrees. We interpret this as evidence that the cortical substrate that processes spatial information has a hexagonal two-dimensional organization, preserving the hexagonal packing of the foveal photoreceptors.