Octopuses have excellent sight, smell and touch. Each of their suckers has small and touch sensors capable of identifying even the smallest of scents or hints of a food source. They are however deaf with no auditory capability at all.
Their eyes slit-shaped pupils are well suited for the light levels which an octopus typically finds itself, but they do not appear to have color vision although they do distinguish polarization of light which may explain why they can mimic surrounding colors so well.
Two special organs called statocysts attached to the brain allow the octopus to orient its body and an autonomic response keeps the eyes oriented horizontally at all times.
Octopuses have an excellent sense of touch, and each sucker has chemoreceptors to allow it to taste what it touches. Each arm also contains tension sensors to allow it to know when they are stretched out but since each limb has some independent capability and the octopuses has very poor proprioceptive senses it is not always capable of determining the exact position of its body or arms at any given time. Due to this an octopus can’t tell the overall shape of an object it is handling (stereognosis) although it can detect texture variations on a local level.
The unique autonomy of the arms causes some difficulty for octopuses learning effects of its motions – to see what reaction the arms have taken to a high-level command means visually observing as there is no direct feedback to the brain from the arms themselves.
The neurological autonomy of the arms means that the octopus has great difficulty learning about the detailed effects of its motions. The brain may issue a high-level command to the arms, but the nerve cords in the arms execute the details. There is no neurological path for the brain to receive feedback about just how its command was executed by the arms; the only way it knows just what motions were made is by observing the arms visually.