Evidence for the Intraocular Discrimination of Vertically and Horizontally Polarized Light by Octopus

Abstract

1. Four groups of octopuses (6 animals in all) were trained to discriminate between vertically and horizontally plane-polarized light. Two different sources of polarized light were used: a torch, and a disk of polaroid backed by white plastic. Half the octopuses were trained using the former source, and half using the latter. 2. With each polarized light source, discrimination could be based on a reflexion or scattering pattern, but the extra-ocular cues would be different for the two sources. 3. After training, each octopus was shown, without reward or punishment, the polarized light source with which it was not trained. The aggregate score shows efficient transfer, and three of the four groups showed a significant preference for the new source when the plane of polarization was the same as that which they were trained to attack. 4. It is concluded that the discrimination is not based on extra-ocular patterns, i.e. that the analysis of the polarized light occurs within the octopus's eye.