Modeling self-organizing tri-chromatic color selective regions in primary visual cortex

Abstract

How does the brain represent and process color inthe primary visual cortex (V1)? Experimentalevidence from macaque monkey suggests that cellsselective for color are organized into small,spatially separated blobs in V1. This organizationis strikingly different from that of orientation andocular dominance maps, which consist of large,spatially contiguous patterns. In this paper, aself-organizing tri-chromatic model of V1 isconstructed using natural color image input. Neuronsin the modeled V1 are initially unselective, anddevelop multi-lobed ON/OFF receptive fields throughHebbian learning of retinal responses to visualpatterns. The model develops realisticcolorselective receptive fields, color maps, oculardominance columns, and orientationmaps. Color-selective blobs are located insideocular dominance columns, and lateral connectionslink cells with similar orientation preferences,matching previous experimental results. Further, themodel makes a number of predictions for futureexperiments, including: 1. The color map has threetypes of color-selective blobs and a unique corticalactivation pattern exists for each of the pure colorhues. 2. The usual blob-like organization for coloremerges as long as the training images have a higherbrightness contour gradient compared to the huecontour gradient, and the inputs are highlycorrelated between the eyes. Otherwise the colorblobs regularly extend across borders of oculardominance stripes (contrary to macaqueresults). 3. Neurons in areas where red and greenpatches are near each other respond to both red andgreen, causing them to maximally prefer yellow, eventhough there are no yellow photoreceptors in theretina. 4. Cells selective for color connect toother cells with similar chromatic preferences:Blue-selective neurons connect to blue selectiveneurons, red-selective to other red-selectiveneurons, and so forth. Thus the model replicates theknown data on the organization of color selectivityin V1, gives a detailed explanation for how thisstructure develops and functions, and providesconcrete predictions that can be tested in futureexperiments. These findings suggest that a singleself-organizing system may underlie the developmentof orientation selectivity, eye preference, colorselectivity, and lateral connectivity in the primaryvisual cortex.