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? What kind of intentional stance do we require to account for it? 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 associative learning is evidence for belief and agency in animals
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. Using our terminology, we might say that unlearned behaviour can be explained in terms of a mind-neutral, goal-centred intentional stance:
L.10 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 F.4), flexible behaviour is a universal feature of organisms, including plants. Dretske employs the terms "mindless", "unlearned" and "hard-wired" inter-changeably. 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 F.6) - 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. Our final conclusion relating to flexible behaviour is that by itself, it cannot serve to identify mental states:
F.7 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 sometimes 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.
The following two conclusions tighten the learning-related criteria for ascribing mental states:
L.12 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.
L.11 A capacity for 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, endeavours to address this question. We will return to it below in the section on representations and mental states. Before we do, I propose to explore the role of controlled movement in our identification of mental states.
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