Annalee Newitz in io9:
They may be tasty when you fry them up, but evidence is mounting that cephalopods like octopuses and squid possess consciousness. Over at the Cephalove blog, neuroscience student Mike Lisieski explains why.
The problem with measuring something like “consciousness” is that there is no agreed-upon definition. However, scientists can use a few basic tools to determine whether animals think in ways that humans would recognize as similar to themselves. You can measure (to a certain degree) whether a creature has self-awareness, independent problem-solving abilities, and exhibits brain activities that resemble “thinking” in the human brain.
In his essay, Lisieski walks us through three of these tests, and explains how cephalopods score.
Learning and object-recognition
First, do cephalopods exhibit self-awareness, which is to say are they aware of their environment and can they learn from it? Very few tests have been designed to suss this question out – partly because it's difficult to find a good cephalopod equivalent to the tests we do on rats, where the rodents learn to do tasks for a food reward. However, there were tests done on cephalopods in the 1970s where, as Lisieski puts it:
It was eventually concluded that octopuses (that is, individuals of the species O. vulgaris, the common octopus) don't use a set of simple rules to categorize objects. Rather, Mather argues, they “[evaluate] a figure on several dimensions and [generate] a simple concept, where [a] concept is an abstract or general idea inferred or derived from specific instances.” Other evidence for the ability of cephalopods to exhibit learning like that taken to indicate cognitive ability (and thus the potential for consciousness) in vertebrate species comes from more complex learning tasks. The spatial learning abilities of cephalopods have been studied and it has been found, in general, that they might be capable of spatial learning to rival that of commonly used vertebrate laboratory species (such as rodents).