Multiplicative modulations in hue-selective cells enhance unique hue representation

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. Beyond LGN, studies on multiple regions in the ventralThe color processing mechanisms in the primary visual stream show an increase in nonlinearity with respect tocortex and later processing stages are a target of debate the three cone types from LGN to higher brain areas [7]among color vision researchers. What is also unclear is and also a shift of selectivity toward intermediate hueswhich brain area represents unique hues, those pure colors in the MB diagram with more diverse selectivity in laterunmixed with other colors. Specifically, in V1, some suggestedon color mechanisms in higher visual areas, human that neurons representing local hue have single-opponentvisual system studies confirm that color encoding starts receptive fields similar to LGN cells [9, 10] with comparablewith three types of cones forming the LMS color space. In contrast, Wachtler et al.[12]mechanisms such as those in LGN were the basis of the found that the tunings of V1 neurons are different from"Opponent Process Theory" of Hering [2], where he introduced LGN and that the responses in V1 are affected by context.unique