International Journal of Comparative Psychology

Goldfish pressed a paddle

for intermittent food reinforcement in the presence of one of seven different monochromatic wavelengths. Wavelengths in 20nm steps from 430 to 690 nm, matched for "brightness," were then presented for 20 days during which food maintained responding to the training stimulus. Generalization gradients calculated from the final four days were asymmetric. A long wavelength gradient showed maintained responding above 630 nm; at short wavelengths responding generalized below 490 nm; four middle wavelength gradients could indicate two groupings having maximum responses at around 510 and 570 nm.