The receptive field construction of midget ganglion cells in primate retina

The midget pathway of the primate retina provides the visual system with the foundations for high spatial resolution and color perception. An essential contributor to these properties is center-surround organization, in which responses from the central area of a cell's receptive field are antagonized by responses from a surrounding area. Two key questions about center-surround organization are unresolved. First, the surround is largely or completely due to negative feedback from horizontal cells to cones: how can this feedback be reconciled with the popular difference of Gaussians (DOG) model, which implies feedforward inhibition? Second, can the spatial extent of center and surround be predicted from the components-optics, horizontal cell receptive field, ganglion cell dendrites-that give rise to them? We address these questions with a computational model of midget pathway signal processing in macaque retina; model parameters are derived from published literature. We show that, contrary to the DOG model, the surround's effect is better treated as divisive. A simplified version of our model-a ratio of Gaussians (ROG) model-has practical advantages over the DOG, such as accounting for spatiotemporal interactions and pulse responses. The ROG model also shows that both center and surround radii can be calculated from a sum of squared radii of their components. Finally, chromatic antagonism between center and surround in the full model predicts cone opponency as a function of eccentricity. We suggest that a signal-processing model gives new insight into retinal function.<b>NEW & NOTEWORTHY</b> We simulated signal processing from cones to midget ganglion cells in the monkey retina and found that: <i>1</i>) center/surround structure is better described as a ratio of Gaussian functions than as the traditional difference of Gaussians; <i>2</i>) ganglion cell center and surround radii can be calculated from a sum of squares of radii in upstream stages; <i>3</i>) the model can predict chromatic dominance in the center and surround mechanisms as a function of eccentricity.