This chapter considers the psychophysical, physiological, and anatomical evidence for orientation channels and their arrangement, and then considers evidence with respect to the relation between orientation and spatial frequency selectivity. The chapter shows that there are both multiple spatial frequency channels and multiple orientation channels, based on deductions from psychophysical experiments. Second it is shown that in each section of the striate cortex there are cells with band-pass tuning for both orientation and spatial frequency, that is, for two-dimensional spatial frequency. Third the chapter demonstrates that the ensemble of cells within a region has two-dimensional spatial frequency selectivities scattered over the whole range of two-dimensional spatial frequencies to which the visual system is sensitive in that area, as a result of a systematic relationship between the columnar organizations for orientation and spatial frequency. Finally it is shown that the orientation tuning does not change significantly with spatial frequency or vice versa in most cells.
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