Abstract
Purpose::
Color contrast is the phenomena that the color of an object shifts in the direction of the complementary color of the surround. It has been suggested that the neural basis for color contrast are spectrally opponent neurons. We ask the question whether such processing indeed needs spectral opponency. Last year we presented evidence that at the photoreceptor - horizontal cell synapse a gain control mechanism is functioning that increases the gain of the synapse with surround stimulation (Kamermans et al., ARVO 2006). Now we investigate the spectral dependence of this mechanism.
Methods::
Patch-clamp, intracellular and extracellular recordings were made from respectively cones, horizontal cells and ganglion cells in the isolated goldfish retina. The retina was stimulated with spots of sine wave modulated light with various contrasts, intensities and color. The influence of sustained surround stimulation on the responsiveness of the neurons was studied.
Results::
We will show that steady surround stimulation of the inhibitory surround of the ganglion cells leads to a potentiation of the center responses of ganglion cells to sinusoidal modulated light in the center. In spectrally non-opponent neurons, a colored surround leads to a sensitivity shift of the center response to the opponent color of the surround, illustrating that 1) color contrast is present at the ganglion cell level and 2) that color contrast is (also) mediated by spectrally non-opponent neurons.
Conclusions::
Color contrast is observed at ganglion cell level in spectrally non-opponent neurons. The underlying mechanism for the generation of color contrast is negative feedback from horizontal cells to cones.
Keywords: retina: distal (photoreceptors, horizontal cells, bipolar cells) • retina: proximal (bipolar, amacrine, and ganglion cells) • color vision