A model of tool use in Cephalopods

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Photo of a giant Pacific octopus. Copyright Greg Dombowsky and Dive BC Publications.

What is a cephalopod?

Cephalopods are a class of the phylum Mollusca (molluscs) and are therefore related to bivalves scallops, oysters, clams, snails and slugs, tusk shells and chitons. Cephalopods include the pelagic, shelled nautiloids and the coeleoids (cuttlefish, squid and octopods, the group to which octopuses - not octopi - belong). Among molluscs, cephalopods are renowned for their large brains, while other molluscs (e.g. bivalves) lack even a head, let alone a proper brain.

An overview of the cephalopods, their relationships to other animals and their cognitive abilities can be found in the Appendix.

Fine tuning in octopuses

Octopus arms are highly manoeuvrable. Courtesy BBC.

Most cephalopods have very flexible limbs, with unlimited degrees of freedom. Scientists have recently discovered that octopuses control the movement of their limbs by using a decentralised system, where most of the fine-tuning occurs in the limb itself:

...[A]n octopus moves its arms simply by sending a "move" command from its brain to its arm and telling it how far to move.

The arm does the rest, controlling its own movement as it extends.

"There appears to be an underlying motor program... which does not require continuous central control," the researchers write (Noble, 2001).

When discussing insects, I argued that there is no reason why intelligence should be tied to a brain. We should be open to the possibility of creatures who think with their arms, especially when "each arm is controlled by an elaborate nervous system consisting of around 50 million neurons" (Noble, 2001).

The following discussion focuses principally on the well-studied common octopus, Octopus vulgaris.

A model of agency involving tool use

The case of tool use is similar in some ways to operant agency, except that there is no need for a temporal correlation mechanism, and the activity required to attain one's goal is performed with an external object, and not just one's body.

Beck (1980) proposed that in order to qualify as a tool user, an animal must be able to modify, carry or manipulate an item external to itself, before using it to effect some change in the environment (Mather and Anderson, 1998).

We can now formulate a set of sufficient conditions for agency in tool use:

Definition - Agency in the context of tool use
DF.3 An animal can be described as using a tool intentionally if the following features can be identified:

(i) a goal or end-state, which is internally encoded as a stored visual memory involving a tool that the animal associates with attaining its goal;

(ii) motor programs, which are stored in the brain, and generate the suite of the animal's motor output;

(iii) a tool - that is, an item external to the animal, which it modifies, carries or manipulates, before using it to effect some change in the environment;

(iv) an action selection mechanism, which allows the animal to make a selection from its suite of possible motor response patterns and pick the one that is the most appropriate to its current circumstances;

(v) fine-tuning behaviour: an ability to stabilise one of its motor patterns within a narrow range of values, in order for to achieve its goal using the tool;

(vi) the ability to store and compare internal representations of its current motor output while using the tool (i.e. its efferent copy, which represents its current "position" on its internal map) and its afferent sensory inputs;

(vii) associations between different tool-using motor commands and their consequences, which are stored in the animal's memory;

(viii) a pathway for reaching its goal, which is internally encoded as a stored memory of a sequence of movements, coupled with sensory feedback, which allows the animal to steer itself (and its tool) towards its goal;

(ix) sensory inputs that inform the animal whether it has attained its goal with its tool, and if not, whether it is getting closer to achieving it;

(x) self-correction: abandonment of behaviour that increases, and continuation of behaviour that reduces, the animal's deviation from its desired state.

According to Beck's criterion for tool use, octopuses use both rocks and water jets from their siphons as tools to modify their environment. After selecting a place for a home, an octopus usually has to modify it extensively to render it suitable for habitation, as it is usually clogged with sand and the shape may not be appropriate. The octopus gathers up excess sand and small rocks and carries them out to the entrance of its new home. Once there, it lets go of the rocks and blasts them all away with a jet of water from its siphon. After removing sand and small rocks from its burrow, an octopus may be left with a large entrance, so it goes outside, picks up some some small rocks and brings them back to the home, piling them up at the entrance (Mather and Anderson, 1998).

Octopuses also use water jets to get rid of nuisances:

After capturing crab prey, the octopus will usually kill them and hold one or several under the arm web, dissolve the cartilage holding the joints together, digest out the meat, and keep the exoskeleton bits. When it's finished, it will take the remains to the den entrance and jet the lot out into what becomes a midden. If a scavenging Serranid fish comes by to eat these remains, the octopus may jet a blast of water to remove the 'pest' from the vicinity (Mather and Anderson, 1998).

The problem with Beck's yardstick is that the tool-using behaviour it describes may be either fixed or flexible. The behaviour described above may turn out to be a fixed action pattern, and even Mather and Anderson (1998) admit that octopuses use tools "in a very simple way".

Although octopuses do not appear to fine-tune their behaviour when cleaning their dens, they aim their jets carefully at passing scavengers or human observers - rather like a water gun (Mather and Anderson, 2000). This could be an instance of bona fide agency.

Mather and Anderson (1998) also describe a recent experiment (discussed in the Appendix) where two octopuses were able to fine-tune the force of their water jets to control the movement of some coloured toys floating in their tank. The octopuses did not manipulate the toys in a stereotypical fashion; indeed, their behaviour seemed spontaneous, even playful. This tool-using behaviour by octopuses appears to have been both flexible and fine-tuned, but follow-up studies are warranted.

At present, then, there are promising leads, but the evidence is insufficient to determine whether tool use in octopuses is accompanied by cognitive mental states.

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