Color-selective cells in macaque monkey V1 are organized into small, spatially separated blobs, and several studies have shown that these tend to be centered within ocular dominance columns. Recent work has further shown that all hues are represented within each blob, that perceptually similar hues are adjacent (often in the form of a pinwheel), and that these color blobs correspond to CO patches (Xiao et al., Neuroimage 2007 35: 771-786; Lu and Roe, Cereb Cortex 2008 18: 516-533). This organization of color preference into blobs is strikingly different from maps of orientation preference and ocular dominance, which consist of large, spatially contiguous patterns. Here we present a developmental model showing how this organization depends on the statistical distribution of colors in sets of natural images. The model consists of fixed subcortical pathways and a model of V1 that develops through Hebbian learning. Each eye and the corresponding LGN region is modelled as sets of L, M, and S photoreceptors coupled with luminosity, red-green opponent, and blue-yellow coextensive ganglion cells. Afferent connections to a LISSOM-based model of V1 from the ganglion cells are initially random, but develop through Hebbian learning. Lateral excitatory and inhibitory connections within V1 are also initially random and can similarly be modified by Hebbian learning. An initial 'prenatal' phase of spontaneous activity results in the formation of realistic ocular dominance and orientation preference maps, while subsequent presentation of natural images after 'eye opening' results in the emergence of color blobs centered in ocular dominance columns, in regions of lower orientation selectivity. Color-selective cells connect laterally at long ranges to cells with similar chromatic preferences, and an activity ('metabolic') measure in the model shows the equivalent of CO patches corresponding to color blobs. In control simulations, we show that the model results depend crucially on the input's balance of luminance to hue contours, and the relative balance of hues. Depending on these factors, the model can develop either a continuous color map or realistic isolated color blobs. In the case of blobs, the model can develop either a single color preference per blob or pinwheel blobs with all colors, leading to preferences for either primary colors alone or also a range of intermediate colors. These results suggest specific developmental experiments to be run on animals in order to test the assumptions of the model. The simulator and model used for these experiments are freely available from topographica.org.
|Publication status||Published - 2009|
|Event||Society for Neuroscience Annual Meeting 2009 - Chicago, United States|
Duration: 17 Oct 2009 → 21 Oct 2009
|Conference||Society for Neuroscience Annual Meeting 2009|
|Period||17/10/09 → 21/10/09|