Does associative learning require a mind?

Back to Worm page Previous page Next page References
*** SUMMARY of conclusions reached

The fireworm. Courtesy of Coral Reef Network, Hawaii.

Does the flexible behaviour of "simple" worms qualify as learning?

Regardless of whether they can control their behaviour, nematode worms are certainly capable of associative learning - i.e. "true" learning as defined by Kilian and Muller (2001). Should philosophers call this "learning"?

I believe that philosophers should respect the norms of popular usage when using everyday words. In keeping with these norms, I suggested earlier that the word "learning" be reserved for mental states, wherever possible. However, popular norms may clash in special cases. I also quoted a dictionary definition, according to which acquiring a skill by experience qualifies as learning. There is good evidence that some worms, whether or not they possess mental states, are capable of acquiring skills through experience. They can be conditioned to avoid a stimulus that they were previously attracted to. The ability to change one's preferences may turn out to be biologically useful for an animal, so it surely deserves to be called a skill. I suggest that we should regard conditioning as a form of experience (i.e. training) without committing ourselves at this stage as to worms have subjective inner states. Being conditioned to change one's preferences is therefore acquiring a skill through experience. It follows that some worms can learn, regardless of whether they have mental states or not. They are "educable" creatures.

L.6 The ability of an organism to undergo associative learning (classical and/or instrumental conditioning) is a sufficient condition for its being able to learn, in the proper sense of the word.

To sum up: recent research has shown that roundworms (nematodes) are capable of associating stimuli when they undergo classical conditioning. These simple worms represent a breakthrough in mind-like behaviour: they are educable creatures, capable of true learning. However, it has not yet been shown that they are capable of genuine trial-and-error learning (operant behaviour, as defined by Abramson). More research needs to be done on flatworms (platyhelminthes) before we can say that they are even capable of true learning.

Daniel Dennett. Photo courtesy of University of California.

Dennett (1997, p. 112) describes organisms with a capacity for associative learning as "Skinnerian creatures". They occupy the second level in his hierarchy of mind-like organisms (1997, pp. 109 ff.), above Darwinian creatures (described in the section on viruses). Unlike Darwinian creatures, Skinnerian creatures have bodies whose response patterns can be altered by their experiences. A Skinnerian creature is capable of getting positive or negative feedback about its actions, which makes it more likely to select an advantageous course of action and avoid misfortunes in the future (this is what we call operant conditioning). Such a creature can learn from its trial-and-error mistakes and successes - in other words, it can associate information about one kind of event with information about another kind. At this level of cognition, trial-and-error improvement goes on inside the creature's brain and nervous system, instead of at the genetic level.

Do roundworms qualify as "Skinnerian creatures"? If we adopt Dennett's definition of "Skinnerian creatures" as organisms with a capacity for associative learning, whose response patterns can be altered by their experiences, the answer is yes. However, Dennett also defined Skinnerian creatures as animals that are capable of trial-and-error learning from their past mistakes and successes, i.e. operant conditioning (1997, p. 112). On this criterion, it is not clear that roundworms qualify. It may turn out that there are creatures that are capable of associative learning but incapable of operant behaviour. Dennett may have conflated two stages in his mental hierarchy.

Does associative learning require a mentalistic explanation?

Ivan Pavlov.

So far, it has not been established that associative learning is a mental process. To do this, we have to ask: what kind of intentional stance should we use to explain it? Does it indicate the presence of mental states in an animal, or whether it can be explained using cognitively neutral terminology? The question remains a controversial one. As we shall see, the term "associative learning" describes a complex cluster of abilities, which vary between different kinds of organisms.

At first blush, it may seem that associative learning is best described in mentalistic terms, as the animal actually learns to respond to a stimulus in a new way. However, from the beginning, some pioneers of learning research have championed a non-mentalistic account of conditioning. The most famous debunker of mentalism was Pavlov, who proposed his stimulus substitution theory to explain the conditioning process: all that happens is that the unconditioned stimulus (US) is substituted for the conditioned stimulus (CS), in eliciting a response. The conditioned response (CR) and unconditioned response (UR) are exactly the same. The animal does not actually learn anything; a new neurological connection is formed in its brain, and nothing more. The inadequacies of Pavlov's theory are reviewed by Brembs (1996) and discussed in an Appendix.

At present, there is no scientific consensus regarding the cognitive requirements of associative conditioning. However, some philosophers have proposed drawing a line between creatures that are "educable" and those that are not. The former are said to have beliefs that are acquired and modified through conditioning (Dretske, 1999). On other cognitive accounts, educable creatures are said to have expectations that they can bring about certain outcomes (Beisecker, 1999). These creatures continually revise their expectations by being sensitive to the consequences of their actions. Although both accounts acknowledge that educable animals can make mistakes, this feature is central to Beisecker's account.

Dretske: why operant conditioning is evidence for belief and agency in animals

Fred Dretske. Photo courtesy of Stanford University.

Dretske (1999) has argued that animals capable of undergoing operant conditioning are capable of not only memory and learning, but also belief and agency. He carefully differentiates agency from behaviour: behaviour may have a meaning, but purposeful acts are governed by their meaning. When an action occurs, events that have a meaning cause an animal to behave in a certain way, by virtue of their meaning. With computers and plants, on the other hand, events which have a meaning we can recognise, cause something to behave, but it is the intrinsic properties of the events, and not their meaning, that explains the behaviour.

Dretske illustrates his point with a few well-chosen examples. A speaker utters the words "Vibrate rapidly" into a microphone. The microphone's diaphragm vibrates rapidly. The sounds made by the speaker had a meaning - "Vibrate rapidly" - but it is not what the speaker says, but the physical properties of the sounds, which cause the diaphragm to vibrate rapidly. (The microphone would have vibrated rapidly even if the speaker had said, "Be still".) The microphone is sensitive to sound, not meaning.

A thermostat turns the heat on and off, keeping the room at a comfortable temperature. Is this mere behaviour or is it action? We could say that the thermostat simply behaves because it lacks beliefs and desires: a goal-centred intentional stance suffices to explain its behaviour. But Dretske goes beyond this obvious response and attempts to explain what would be needed to make the thermostat's behaviour a bona fide action.

Most thermostats have a bimetallic strip that functions as a thermometer (its degree of curvature represents room temperature) and as a switch - if the room cools to the desired temperature, the strip touches an adjustable contact, whose position corresponds to the room's desired temperature, thereby closing an electrical circuit to the furnace and turning the heat on. The thermostat senses a drop in temperature and corrects it. Although the curvature of the thermostat's bimetallic strip means something (it represents the ambient temperature), it is not the meaning, but the curvature, that governs the thermostat's behaviour. Dretske argues that if we take away the meaning but keep the curvature (e.g. by bending the strip with a pair of pliers), the thermostat will behave the same as it would if the room were cool.

Now consider a foraging bird, who tries to eat a Monarch butterfly that has been reared on a toxic form of milkweed. Eating the butterfly makes the bird vomit. The next day, the bird sees a Viceroy butterfly, which looks remarkably like the poisonous Monarch. The bird flies away. Why does the bird not eat the Viceroy? Its behaviour can readily be explained in terms of operant conditioning: it learned to avoid the stimulus (Monarch butterflies) after a punishing experience, and its internal representation of a Monarch butterfly caused it to avoid a similar-looking butterfly. Whereas a thermostat is hard-wired to behave as it does, the bird's behaviour is triggered by its memory (stored internal representation) of an unpleasant experience, where it learned that a Monarch was poisonous.

Learning of this sort (operant conditioning) consists in harnessing these internal representations to control circuits so that behaviour will occur in the external conditions on which its success depends. Like the thermostat..., this internal representation ... has both a meaning and a causal role, but, unlike the instrument..., its meaning explains its causal role" (Dretske, 1999, p. 10, italics mine).

The nub of Dretske's account is that many animals have a learning history which imparts a meaning to their experiences. It is this meaning which explains their causal role in animal behaviour. When animals use what they have learned to achieve their goals, they are agents. Of course, biologically adaptive hard-wired behaviour (e.g. reflexes) in animals is not agency: it is not learned but automatic, and its efficacy is independent of any meaning (or biological purpose) it may have.

N.16 An organism must be capable of learning before it can be said to have cognitive mental states.

The bird's internal representation causes the avoidance behaviour precisely because it means something about its external environment (i.e. that a certain kind of butterfly is present - the sort of butterfly the bird, after its unpleasant experience, wants to avoid). In this case, we cannot isolate the meaning from the physical properties of the representation and say that the latter, and not the former, cause the behaviour. Here, according to Dretske, we have bona fide agency: the bird has learned the Monarch butterflies are poisonous, it believes that the Viceroy butterfly is a Monarch, and so it flies away to avoid the Viceroy. Dretske uses the word "belief" rather than "knowledge" here, because the bird is in fact mistaken.

Plants, on the other hand, cannot act, according to Dretske. The adaptive behaviour of the Scarlet Gillia illustrates why. Even though this plant can change colour from red to white in summer, thereby attracting pollinators, its adaptive behaviour is triggered not by its "meaning" or biological significance, but by the intrinsic properties of the chemical switches that cause its behaviour, coupled with the historical fact that similar behaviour by its evolutionary forebears, from whom it inherited its genes, enables it to reproduce successfully.

In my opinion, Dretske does an excellent job of explaining why we say that machines and plants behave rather than act, but his defence of agency in animals is marred by an equivocation in the use of the word "meaning". "Meaning", in popular parlance, has both an objective connotation ("significance") and a subjective one ("aim" or "intention"). Dretske makes no attempt to differentiate between them. A thermostat's behaviour has a subjective "meaning" for us: it makes us feel comfortable. On the other hand, the behaviour of the Scarlet Gillia only has "meaning" in the objective sense, as it is biologically adaptive. What about conditioned behaviour in animals?

Dretske has made it clear (1995) that he regards animals with beliefs as conscious subjects. However, if Dretske were trying to rigorously demonstrate that conditioned behaviour in animals could be described as agency because it had a subjective meaning, then he would be clearly begging the question.

In fact, Dretske seems to be making a suasive case (rather than a strictly logical one) for belief in operantly conditioned animals. He appears to be arguing that a belief-based account makes sense of the fact that the bird changes its behaviour because of what it remembers:

Notice how natural it is in this case (unlike the case of the plant or the thermostat) to explain the bird's behavior in terms of what it believes. It is natural, I submit, because memory about some previously experienced object is so obviously implicated in why the bird behaves as it does... Talk of memory becomes appropriate here because behavior changes after a perceptual encounter.. The thermostat and the plant come into the world hard-wired to behave the way they do. What happens to them is not relevant to why they behave that way... Not so with the bird (1999, pp. 28-29, italics mine).

If we look at Dretske's writings, we can discern two criteria by which he claims to distinguish between organisms with and without beliefs. The wording above suggests the following criterion:

Dretske Mark I:

We can use the criterion of learned, flexible behaviour to distinguish between believing and non-believing organisms: whereas the thermostat and the plant are "hard-wired" (1999, p. 29) to behave as they do, the bird is not. It can learn.

This criterion is a little muddled: as we saw above (Conclusion R.6), flexible behaviour is a universal feature of organisms, including plants. However, learned flexible behaviour is restricted to certain kinds of animals. Can we draw the line here?

Dretske's case would collapse at once if a parallel case could be found where he would be unwilling to ascribe belief to the organisms concerned. I discuss three such alleged cases in an Appendix: conditioning of the autonomic nervous system, of leg withdrawal in cockroaches, and of flexion of the hind legs within the spinal cords of paralysed rats.

These three examples undermine the notion that flexible behaviour patterns - even those that are generated by an internal mechanism (Conclusion N.12) - can serve to distinguish organisms with beliefs from those that lack them.

In a similar vein, other researchers have argued that the process whereby animals learn to form associations is too innate to qualify as genuine cognition:

To most minds ... cognition implies an ability to step outside the bounds of the innate, including the innate wiring that enables animals to learn through classical and operant conditioning. It means, instead, a capacity to perform mental operations or transformations and thus to plan or make decisions (Gould, 2002, p. 41).

This definition of cognition (which I assume is meant to be a mentalistic term) proposed by Gould is stricter than the definitions of learning proposed by Kilian and Muller (2001) or Beisecker (1999). An animal's internally driven mechanism for acquiring new behavioural patterns may be considered as a sequence of instructions in one of the animal's internal programs. Gould is arguing that even though an animal may have such an internal mechanism, the mechanism itself may operate according to fixed rules when acquiring these patterns. As the environment fluctuates, new behavioural patterns are acquired, but the "hard-wired" mechanism by which patterns are acquired remains the same: only the content varies. A mind-neutral goal-centred intentional stance appears adequate to explain this kind of behaviour. Even internally generated flexibility of behaviour patterns can no longer be regarded as a hallmark of cognition.

S.13 The presence in an organism of flexible behaviour patterns that are acquired through an internal mechanism does not provide a sufficient warrant for our being able to ascribe cognitive mental states to it.

Since the ability to acquire new behaviour patterns is a primitive kind of learning, it follows that learning can be understood in mind-neutral terminology: in its simplest form, it is the acquisition of a skill, as explained previously. All organisms have survival skills, by virtue of their history. What is unusual about learning organisms is that they have an internal mechanism that allows them to vary their patterns of responding to their surroundings. Following the methodology I have adopted, we should prefer this mind-neutral interpretation unless a mentally richer account proves to be more scientifically productive.

S.14 A capacity for learning in an organism does not provide a sufficient warrant for our being able to ascribe cognitive mental states to it.

S.15 A capacity for associative learning in an organism does not provide a sufficient warrant for our being able to ascribe cognitive mental states to it.

All learning, including human language acquisition, is to some extent innately driven, as Gould himself acknowledges (2002, p. 44). But instead of pessimistically concluding that "by the strictest standards, perhaps there is no genuine cognition in any species, our own included" (2002, p. 44), I believe it would be more profitable to search for cognition by examining what it is that newly acquired behaviour patterns enable their owners to do.

Dretske's second criterion for distinguishing organisms with beliefs from those without, appears to address this problem. As we saw, Dretske's first criterion was carelessly worded: the terms "mindless", "unlearned" and "hard-wired" were taken to be co-extensive, whereas in fact, organisms can sometimes learn new patterns of behaviour mindlessly. In his second criterion, Dretske proposes the capacity to undergo operant conditioning as a yardstick for having beliefs, and ties it in to the notion of control:

Dretske Mark II

Learning of this sort (operant conditioning) consists in harnessing these internal representations to control circuits so that behaviour will occur in the external conditions on which its success depends (1999, p. 10, italics mine).

How are we to understand Dretske's claim that operant conditioning can be understood in terms of internal representations linked to a controlled behavioural response? Two readings are possible. On a "maximalist" reading (which I shall defend below), an organism with beliefs is one that can use its internal representations of its environment, acquired through learning, to control its surroundings. This reading suggests a notion of organisms as agents.

On an alternative "minimalist" reading (which appears to be Dretske's own view), operant behaviour is simply behaviour that is controlled by an organism's internal representations of its environment. Dretske upholds a thorough-going naturalistic, causal account of representation which eschews appeal to "interpreters" as the arbiters of what counts as a representation. Representations, on his account, are indicators which carry information about lawlike connections (say, between As and Bs), but they are something more. Representations, unlike indicators, can be mistaken, because they have a function which they can fail to perform. More precisely, representations are indicators whose natural function is to indicate as they do, because doing so confers a selective advantage on the organism possessing them. Representations, unlike other natural indicators, are not hard-wired: they acquire a function for an animal only when the animal learns what they indicate. Belief-type representations are recruited as causes of bodily movements in an animal because the animal learns what they indicate. Thus beliefs are both reasons and causes of actions (Ryder and Martin, 1999, pp. 5-7; MacFarlane, 2003; Pitt, 2002).

In Dretske's account of operant conditioning, unlike Abramson's, internal representations play a causal role in operant behaviour. It would be beyond the scope of this thesis to adjudicate between competing theories of mental representation (summarised in Pitt, 2002).

While Dretske has drawn attention to the fact that representations have an evolutionary history, insofar as they confer a selective advantage on their possessor, I believe that his minimalist account of belief is not powerful enough, on its own, to distinguish organisms with beliefs from those without. In particular, his account thus fails to distinguish operant behaviour from mere instrumental conditioning, which as we saw above (Conclusion S.15) can occur even in the absence of a mind.

We considered three cases above where conditioning occurred in the absence of belief: conditioning of the autonomic nervous system (ANS) in an astronaut, of leg withdrawal in cockroaches, and of flexion of the hind legs within the spinal cords of paralysed rats. Dretske could claim that in these cases, the systems involved are not forming representations. But in fact, the ANS is representing its external environment, and its function is undeniably a natural, biological one. Moreover, some kind of learning is going on: in space, the astronaut's ANS learns not to compensate for loss of blood to the brain when she stands up, and once the astronaut returns to earth, her ANS has to re-learn this skill. Why does this not qualify as operant conditioning?

Dretske's own example of the bird that shuns the Viceroy is a dubious example of operant conditioning. According to Dretske, the bird believes that the Viceroy tastes unpleasant, and I would certainly agree with him that this ascription of belief to the bird is correct and natural. But in this case, the bird can hardly be said to be engaging in operant behaviour, properly speaking: it is merely avoiding an object that resembles a noxious stimulus. (Abramson would classify this as instrumental behaviour.) One might attempt to explain the bird's change of behaviour using a mind-neutral goal-centred intentional stance, according to which memory can be understood simply as stored information, and learning as a process by which the bird, as an educable animal, acquires new information enabling it to alter its behaviour patterns.

Finally, Dretske's minimalist account fails to explain why behaviour controlled by representations has to be envisaged in mentalistic terms. For Dretske, "controlled behaviour" appears to be synonymous with behaviour caused by representations - defined as learned connections between As and Bs, which serve a biological function. But causation per se is not a mentalistic notion. Likewise, Dretske's notion of representation is too weak to sustain mentalistic inferences. For him, the decisive features of representations are that they carry information which indicates something about the world, they confer a selective advantage on their possessor and they are learned. As we have seen (Conclusions N.2, N.5, S.3, S.14), these properties are necessary conditions but not sufficient warrants for the ascription of mental states.

S.16 The presence in an organism of Dretskean representations, defined as indicators acquired through learning which serve a biological function, does not provide a sufficient warrant for our being able to ascribe cognitive mental states to it.

These deficiencies might be remedied by adopting a richer notion of representation. In the section on insects, I shall argue that representations have a distinctive internal structure, drawing upon several themes that have been discussed in this section: action selection, fine-tuning, control, trying, associations, means and ends (goals). I shall also argue that this rich structure also elucidates the notion of control, linking it to agency, and allows certain kinds of representations to serve as beliefs through which agents control their actions.

Beisecker on belief

David Beisecker. Photo courtesy of University of Nevada, Las Vegas.

Whereas for Dretske (1999) the salient feature of beliefs is that they are internal representations, acquired through learning, which bring about changes in organisms' behaviour, for Beisecker (1999) the defining quality of beliefs is that they can be correct or mistaken. As he puts it:

...the hallmark of intentional states is their susceptibility to evaluation. For instance, a doxastic (or belief-like) state can be correct or mistaken depending upon whether or not some state of affairs, identified as its content, actually obtains. Believers are beholden to the way things are. Similarly, conative states (goals, desires, and other "pro-attitudes") may be fulfilled or unfulfilled, depending upon the satisfaction of some content condition. So intentional states are those that are associated with conditions of satisfaction or fulfillment (1999, p. 283).

According to Beisecker, animals capable of operant conditioning should be regarded as having beliefs because they can make errors which they subsequently try to rectify.

Beisecker argues that animals capable of operant conditioning possess a special non-biological kind of intentionality. Unlike other organisms, whose ends are completely biological, these animals can be said to have expectations that their responses to certain kinds of events will bring about certain outcomes. Insofar as a creature engages in behaviour expected to bring about a certain outcome, we may regard that outcome as one of its goals. Beisecker call these goals non-biological, because we can identify them without having to know anything about the creature's biological evolution, which has determined its built-in ends through natural selection.

Of course, expectations may be disappointed: a creature may make errors of commission (when an animal's expectation - say, of obtaining food - is activated and it responds, but the expected consequence does not eventuate) and errors of omission (when the animal fails to respond because its expectation is not activated, but in fact, the response would bring about a desired consequence). But because creatures continually revise their expectations, they can be said to possess a kind of critical rationality:

Insofar as they are disposed to revise their expectations in the wake of the errors described above, educable creatures would be disposed to take steps to avoid similar mistakes in the future. There is of course no guarantee that these revisions will yield future success. The point is just that creatures displaying this sort of educable capacity would take expectation correctness or aptness to be a regulative ideal, at least in the sense that they are disposed to revise error-prone expectations while leaving correct expectations as they are... Since they can be evaluated as having gotten things right or wrong, we are justified in crediting these creatures with some sort of intentional capacity (Beisecker, 1999, p. 303).

Animals that can undergo operant conditioning can be said to be capable of getting things right, because they can (and often do) get them wrong, and they revise their expectations and their responsive behaviour when they are wrong. The capacity to self-correct one's mistakes is a sine qua non for having beliefs.

N.17 An organism must be capable of self-correcting behaviour before it can be said to have cognitive mental states.

Beisecker's proposal deftly handles counter-examples associated with organisms that behave maladaptively, such as the bacteria containing magnetsosomes, which were discussed above. These bacteria should not be described as being "in error" when they move toward the bar magnet instead of the bottom of the water, because they cannot "tailor their responsive dispositions to their particular surroundings" (1999, p. 298), and hence do not qualify as holders of expectations or beliefs. Bacteria do not try to rectify their maladaptive responses, and it was found that a causal account could account for their behaviour. Beisecker's model of animal behaviour makes a novel prediction that the causal account does not: animals that are capable of operant conditioning will revise their mistaken expectations and try to correct their mistakes. However, this "prediction" cannot be considered scientifically productive unless it can be fleshed out in behavioural terms. What kind of behaviour counts as self-correction, and why? Only if we can answer this question will we be able to identify animals with beliefs and desires.

Beisecker has proposed blocking as an example of behaviour that expectation-generating animals would engage in. I shall discuss this particular claim in detail, as it is a highly unusual prediction of one model of associative learning - the Rescorla-Wagner model - whose central ideas are usually expounded using mentalistic terminology.

Is the phenomenon of blocking an indication of expectations in animals?

A useful way to resolve the question of whether conditioning should be envisaged in mentalistic terms or purely causal terms would be to examine the phenomena linked with conditioning, and ascertain whether the key concepts invoked to explain these phenomena can be defined using a mind-neutral intentional stance. If some of the key explanatory concepts turn out to be irreducibly mentalistic, then we should attribute cognitive mental states to educable animals.

One widely discussed model of classical conditioning - the Rescorla-Wagner model - has been interpreted as amenable to mentalistic terminology. While the model is not able to explain all phenomena connected with classical conditioning, it is still regarded as "the 'best' theory of classical conditioning" (Jackson, 2002). Its basic principle is that "the amount of conditioning depends on how surprising the association between the CS and US is. Surprise determines not only if conditioning occurs but how much conditioning occurs. The more unexpected or surprising the US, the more conditioning will occur" (Lipp, 1998, italics mine). Surprise surely qualifies as a mental state.

The Rescorla-Wagner model can account for many of the unusual phenomena related to associative learning. One phenomenon in particular - blocking - which is readily explained by the model, has been interpreted by philosophers (e.g. Beisecker, 1999) as evidence that animals form expectations and hence have mental states:

Several learning theorists have argued that the apparent educability of some creatures is best explained in terms of the adjustment of "expectation-like" structures mediating between sensory input and behavioral output. For example, expectations are a reasonable explanation for the blocking phenomena often observed in actual creatures. Animals that have been trained to associate a conditioned stimulus with an unconditioned stimulus will subsequently fail to associate other stimuli with the unconditioned stimulus, when the latter are presented along with the original conditioned stimulus. For example, rats that have been trained to associate a bell tone with an electric shock will not come to associate a red light with a shock, as long as the red light is consistently paired with the bell tone. The prior conditioning prevents (or "blocks") subsequent conditioning to other, co-varying stimuli. If learning were merely a function of the frequency of stimulus-pairing, then one would expect the animal to become conditioned to the new stimulus as well. One would expect the rats eventually to associate the red light with a shock, as indeed they do when they aren't subjected to the earlier training. Many learning theorists have argued that the failure of previously conditioned animals to become conditioned to the new stimulus arises because the animal already uses the original conditioned stimulus to successfully predict the occurrence of the unconditioned stimulus. When a previously conditioned rat encounters the compound tone and light stimulus, it expects that the shock will occur (because it heard the bell tone), and so the subsequent shock isn't a surprise. Since events are as they were expected to be (they were not novel), there is no pressure to develop new associations, hence no subsequent conditioning to the light. Thus these theorists conclude that the rats are responding to surprise, to things not being as they expected them to be (Beisecker, 1999, pp. 298-299).

If "educable" animals (i.e. those which are capable of associative learning) can make predictions and form expectations, then they must possess mental states. Even simple worms are capable of associative learning. Should we then conclude that at least some worms have minds of their own?

There are two good reasons for questioning this conclusion. First, most kinds of animals that are capable of associative learning have not yet been shown to exhibit blocking (see Appendix for further discussion). There have been no reports of blocking in worms, and its occurrence even in so-called "higher" invertebrates (honeybees) remains controversial. It would be unwise to use the phenomenon of blocking to argue for cognitive mental states in invertebrates.

A second reason for caution is that even if blocking is confirmed in C. elegans, it may turn out to be explicable in non-mentalistic terms. As one neurobiologist who does research in this field commented (Menzel, personal email communication, 21 July 2003):

Expectation is a term that I am also using in these papers but not with a high order cognitive meaning. It is my impression that scientists in my field are considering expectation as a function that results from former learning and creates a status of retrieved memory without implications about any separate cognitive state other than memory retrieval. There are even concepts that try to explain blocking as a function of peripheral sensory integration.

We have already seen that sensory capacities and memory can be explained by adopting a goal-centred intentional stance, without the need for a richer, mentalistic account. If many scientists believe that these capacities are sufficient to explain blocking, then (pace Beisecker) it would be unwise to invoke blocking as evidence of mental states.

S.17 The presence in an organism of blocking does not provide a sufficient warrant for our being able to ascribe cognitive mental states to it.

Back to Worm page Previous page Next page References
*** SUMMARY of conclusions reached