They have long term and short-term memories as do vertebrates. Once the problem is solved, octopuses remember and are able to solve it and similar problems repeatedly. Octopuses sense of touch is acute in it's suckers. The rim of the cups are particularly sensitive. A blindfolded octopus can differentiate between objects of various shapes and sizes as well as a sighted octopus.
Octopuses have highly complex eyes which compare to human visual acuity.
Focusing is done by moving the lens in and out rather than by changing its shape as the human eye dose. When threatened, octopuses will often try to escape by releasing a cloud of purple-black ink to confuse the enemy. It's body will change color, release an ink cloud and jet away to safety. Several blotches of ink can be released before the ink sac is empty. The ink is toxic to an octopus in a confined space such as in a cave with little water current or in captivity.