Octopuses perceive second order motion: Evidence for convergent evolution of visual systems

Abstract

The ability to detect camouflaged prey and predators is important for survival. One plausible candidate mechanism for counteracting camouflage in the environment is second-order motion perception, which requires different, more sophisticated neural circuitry than first-order motion perception. Using an operant conditioning paradigm, we trained octopuses (octopus bimaculoides) to approach the side of a screen containing a second-order motion stimulus: the silhouette of a crab filled with visual noise that moved over a background of similar visual noise. The other side of the screen had only static visual noise. Stimuli were presented on a special wall in the tank that served as a screen for projection. Two halves of the screen were separated by another wall orthogonal to the screen, splitting a small part of the tank into two compartments of equal size, inside one of which the target stimulus was presented. After conditioning, the animals would select the target by entering the correct compartment almost perfectly. Octopuses are an animal model of special interest because they are thought to be endowed with complex cognitive functions, while also having over 500 million years of evolutionary history that is unshared with humans. Cephalopod and mammalian visual systems have evolved largely independently, with their last common ancestor possessing only very rudimentary light sensing organs and visual processing faculties. Convergent evolution of such systems strongly suggests that the trait in question – second-order motion perception – is an optimal solution for a common problem faced by our two species.