Many neurons in the primary visual cortex (area V1) show pronounced
selectivity for the orientation and spatial frequency of visual stimuli,
whereas most neurons in subcortical afferent streams show little
selectivity for these stimulus attributes. It has been suggested that this
transformation is a functional sign of increased coding efficiency,
whereby the redundancy (or overlap in response properties) is reduced at
consecutive levels of visual processing. Here we compared experimentally
the response redundancy in area V1 with that in the three main dorsal
thalamic afferent streams, the parvocellular (PC), koniocellular (KC), and
magnocellular (MC) divisions of the dorsal lateral geniculate nucleus
(LGN) in marmosets. The spatial frequency and orientation tuning of single
cells in the LGN and area V1 were measured, using luminance contrast
sine-wave gratings. A joint spatial frequency-orientation response
selectivity profile was calculated for each cell. Response redundancy for
each population was estimated by cross-multiplication of the joint
selectivity profiles for pairs of cells. We show that when estimated in
this way, redundancy in LGN neurons is approximately double that of
neurons in cortical area V1. However, there are differences between LGN
subdivisions, such that the KC pathway has a spatial representation that
lies between the redundant code of the PC and MC pathways and the more
efficient sparse spatial code of area V1.