Simultaneous color contrast in goldfish--a quantitative study.

A set of 9-15 colored test fields was presented to goldfish. In Experiment 1, test field hues ranged from green through yellow to red; in Experiment 2, the hues varied from blue through gray to yellow. In the training conditions, the test fields were presented with a gray or black surround. The fish learned to choose one intermediate test field hue by rewarding them with food. In the test conditions, the color of the surround was changed from gray to green, or red (Experiment 1), and from black to blue, or yellow (Experiment 2). The choice behavior of the goldfish changed substantially: one of the test fields other than the training test field was preferred. Direction and strength of simultaneous color contrast was quantified in goldfish color space. The effect of spatial stimulus configuration was investigated by changing test field size and using narrow annular surrounds. With test field radii ranging between 2 and 7.5 mm simultaneous color contrast was optimal whenever the ratio between surround width and test field radius had a value of about 1:1.