A Mathematical Model of Retinal Receptive Fields Capable of Form & Color Analysis

In an effort to understand the workings of the retinal receptive fields, Enroth-Cugell and Robson developed a mathematical model that utilized the difference-of-Gaussian (DOG) function, an equation in which the inhibitory portion of a receptive field is subtracted from the excitatory portion. Additions to the original Enroth-Cugell and Robson equation have been successful in modeling a two-dimensional array of different-sized receptive cells. However, this model could be greatly enhanced if it were able to respond to the chromatic characteristics of a stimulus. In this study, the existing model was extended to include chromatic analysis. Using Mathematica, the spectrally opponent nature of the receptive field and the trichromatic features of the cone pigment systems were added to the model via a filter placed before the existing equation. To validate this color sensitive model, the model was exposed to pure color fields that ranged in hue from 400nm to 700nm. The results obtained from this full-field simulation were highly correlated to the findings of past physiological experiments. To further validate the model, two participants performed a series of psychophysical matching tasks involving simultaneous color contrast stimuli. The model was presented with an identical set of stimuli. The results obtained by the behavioral testing were highly correlated with those produced by the model indicating that the color-opponent processing responsible for simultaneous color contrast begin at the level of the ganglionic receptive fields.