Cell responses to drifting Cartesian (parallel) and non-Cartesian
(concentric, radial, and hyperbolic) stimuli were recorded in
and beyond the classical receptive field (CRF) in the lateral
geniculate nucleus (LGN), V1, and V2 of anesthetized monkeys.
Many cells were equally responsive to Cartesian and non-Cartesian,
especially concentric, gratings. Around 15% of cells in each
area were significantly more responsive to concentric compared
to parallel gratings; however, cells significantly more responsive
to parallel compared to concentric gratings were more numerous
in the cortex. While many cells responded to hyperbolic and
radial gratings, few were most responsive to these gratings.
Cell selectivity decreased for Cartesian and increased for
non-Cartesian gratings from V1 to V2 and the relative response
varied as a function of stimulus extent with respect to the
CRF. Complex, nonoriented, nondirectional cells with a low aspect
ratio (AR) responded best to non-Cartesian gratings. These
results cannot be fully explained using Gabor linear/energy models of
simple and complex receptive fields (RFs) although such models predict
some cells to respond equally to Cartesian and non-Cartesian gratings.
Cells significantly more responsive to non-Cartesian gratings can
be accounted for by CRF selectivity influenced by modulation
from the nonclassical receptive field (nCRF). The present study
shows that Cartesian/non-Cartesian selectivity is not an emergent
property of V4 cells but is present at all levels of early visual
processing being subserved by a subset of cells with specific
tuning properties.