Color discrimination conditioning in two octopus Octopus aegina and O-vulgaris.

In order to investigate the color vision in Octopoda, color discrimination conditioning and transposition tests were done with two octopuses, Octopus aegina and O. vulgaris in tanks. The animals were trained to discriminate b y touch between blue (25 mm in diameter, reflectance lambda (max) = 460 nm) and white or light shaded balls (negative balls) for a food reward. The ba lls were presented simultaneously in front of a shelter wherein each animal resided. After the completion of the conditioning, the negative balls were substituted with ones of different shades of gray (G1 to G5 in the order o f reflectance), and transposition tests were done to examine the possibilit y of darkness-based discrimination. In the transposition tests, O. aegina showed correct responses at 70-100% t o the blue ball irrespective of the shades of grey employed, implying the p ossession of color vision. O. vulgaris changed the choosing response with t he shades of gray employed, indicating the darkness-based choosing and lack of color vision; biased to blue at G1, random at G2, biased to gray at G3 and G4 which were darker than the blue, and biased to blue at G5 which was much darker than the blue.