Abstract
The receptive field of H1 horizontal cells in the primate retina is comprised of two distinct components each with different spatial extent (Packer & Dacey, 2005). While a spatially narrow profile of the receptive field is formed by the synaptic input from multiple neighboring cones, an additional spatially-broad profile emerges through the electrical coupling among horizontal cells that enables the long-range signal spreading within the cell layer. Tweaking the biologically-plausible model of the cone-horizontal cell circuit developed by Van Hateren (2005; 2007) and extending the model to include the upper hierarchy of the retinal cell layers, we examined the potential effect of the dual-component receptive-field structure of horizontal cells on the achromatic information processing in the parasol retinal pathway. Model simulations show that while the narrow receptive-field component is responsible for generating local contrast signals at the edge between a pair of adjacent surfaces (equivalent to the classic concept of 'lateral inhibition' through the center-surround receptive field), the broad component contributes to further enhancing the contrast between the surfaces. This contrast enhancement effect is more drastic for a high spatial-frequency stimulus to which the horizontal cell responsiveness is reduced due to the broad component such to enable a stronger feedfoward signal transmission. For a low spatial-frequency stimulus, the enhancement effect is still observed but only at the edge between the surfaces. These results suggest that the horizontal cell feedback mechanism may be one of the ways for the visual system to regulate spatial-frequency dependent contrast sensitivity.