This chapter argues that visual information is encoded in terms of spatial frequency because the visual world is periodic and can thus be more efficiently encoded in the spatial frequency domain than in the pure space domain. However, insofar as visual patterns are only locally periodic, a local but not a global frequency analysis would take advantage of such redundant patterns. It may well be that spatial periodicities in fact rarely extend over more than a small fraction of the visual (...) field. Thus, spatially localized, patch-by-patch spatial frequency encoding would be most adaptive, more so than more global processing. (shrink)