The octopus is very odd.
It is not at all like such mammals as the dog and the monkey, which have brains built on the same plan as humans, even though they are much dumber. The octopus is not a mammal, or even a vertebrate. It is a mollusk, a sort of sophisticated clam. Its brain evolved independently—and the octopus in many ways is an independent thinker. Last week University of Cambridge Zoologist Martin J. Wells was preparing to publish a fascinating study on a far-out subject: the octopus and its intellect.
The main job of any brain is to make the best use of reports from the senses. Wells says that octopus senses are pretty sensible. An octopus eye is built much like a human eye; both have a lens that throws an image on a light-sensitive retina. The chief difference is that the human eye is focused by muscles that change the shape of the lens. In the octopus eye the lens is moved back and forth, like that of a camera, to get a sharp focus. This arrangement seems to work efficiently for octopuses. In fact, the ghastly, slit-pupiled eyes of an octopus may even distinguish between different kinds of polarized light, an accomplishment that human eyes are unable to achieve.
In its eight rubbery arms an octopus has an excellent sense of touch. Its taste sensors, which seem to be concentrated around the rims of the clutching suckers, can detect chemical traces that are barely strong enough to affect a human tongue. It is equipped with a statocyst, an efficient apparatus just below the brain that acts like the gravity perceiver of the human inner ear, telling the octopus which direction is up.
Food & Shocks. The only way to find out what the octopus brain can do with this wealth of sense information is to experiment with a living octopus. Zoologist Wells explains that the octopus likes to select a "home," a cranny or hole in a pile of rocks, and sit there waiting for food to come within grabbing range. Its perception can be tested by tempting it with bits of food or with things that look more or less like food, and it can be educated by a system of rewards and punishments, such as slight electric shocks. The octopus readily learns, for example, that a square card poked at it must not be touched. With it goes a shock. But an oval card should be seized; right behind it comes dinner.
Experiments of this kind have proved that the octopus can distinguish the shapes of objects that it sees and can judge their size and distance. A very large object makes the octopus turn pale and flatten down, presumably from fright. The octopus can tell a vertical object from the same object lying horizontal, but it cannot tell between mirror images—related shapes like right and left hands.
The octopus seems, superficially, to be judging the visual world around it as a dog or human would. But when its gravity-detecting statocyst is removed, it becomes virtually helpless. Apparently its system of telling an object's orientation is to keep its two eyes level, which it does with the help of the statocyst. If this organ is lost, the eyes get out of level, and the octopus no longer knows which way is up —or, for that matter, down. Humans and other higher vertebrates are not handicapped in this way. Their more elaborate brains make allowance for the position of the eyes and keep the world from slanting whenever the eyes slant.