  There is still much to understand about the color processing mechanisms in
the brain and the transformation from cone-opponent representations to
perceptual hues. Moreover, it is unclear which areas(s) in the brain represent
unique hues. We propose a hierarchical model inspired by the neuronal
mechanisms in the brain for local hue representation, which reveals the
contributions of each visual cortical area in hue representation. Local hue
encoding is achieved through incrementally increasing processing nonlinearities
beginning with cone input. Besides employing nonlinear rectifications, we
propose multiplicative modulations as a form of nonlinearity. Our simulation
results indicate that multiplicative modulations have significant contributions
in encoding of hues along intermediate directions in the MacLeod-Boynton
diagram and that model V4 neurons have the capacity to encode unique hues.
Additionally, responses of our model neurons resemble those of biological color
cells, suggesting that our model provides a novel formulation of the brain's
color processing pathway.
