Retinal ganglion cells in the turtle were extracellularly recorded to define the shapes of their receptive fields by small moving light spots. To better define the geometries, spectral-light adaptations and vitreal injections of 2-amino-4-phosphonobutyric acid (APB) were used to disrupt balances in field organization along dimensions of wavelength, ON and OFF responses, and center/surround areas. Three-dimensional data plots were fit by Gaussian, Gabor, and cardioid functions to show that the shapes of receptive fields are predicted by combinations of these multiplied functions. Results indicate that Gaussian functions describe simple symmetrical receptive fields that are center-only; Gabor functions describe center/surround color-opponent receptive fields that have a ring of spike activity in the periphery; and directionally selective receptive fields, in contrast, which are asymmetrical, are described by cardioid functions adjoined to Gaussian or Gabor functions. The advantage of linking multiplied functions is that receptive fields are unified by a model that predicts progressively more complex field geometries derived from particular stimulating conditions.