Meta-learning in insects - (2) concept formation

Concept formation is another area in which meta-learning can be shown to take place in insects. Tests by Gould and Gould (1988) showed that bees could learn to recognise and distinguish human letters, regardless of size, colour, position or font. Giurfa, Eichmann and Menzel (1996) trained foragers to associate symmetrical shapes with food. Asymmetrical shapes were not rewarded. (In another test, asymmetrical shapes were rewarded while symmetrical ones were not.) By the seventh visit, the bees could choose a correct novel stimulus over an incorrect one. Gould argues that this kind of learning differs from associative tasks:

The learning curve is different from that of more standard tests in which bees are taught that a particular odor, color, or shape is always rewarded. During concept learning there is no evident improvement over chance performance until about the fifth or sixth test, whereas in normal learning there is incremental improvement beginning with the first test. This delay is characteristic of what has been called 'learning how to learn', which is interpreted as a kind of 'ah-ha' point at which the animal figures out the task.

The main difference is that honey bees are much quicker at deciphering what the experimenter wants than are pigeons and other standard laboratory animals (Gould, 2002, pp. 43-44, italics mine).

I would agree with Gould's claim that the only satisfactory explanation for the sudden improvement in the bees' performance is a cognitive one: the bees formed a generalised notion of a symmetrical (or asymmetrical) object. Prior associative learning of rewarded and unrewarded stimuli cannot explain their performance, as (a) the relevant property was not a low-level property such as "red" that they were hard-wired to recognise, and (b) the bees had to transfer their discriminatory abilities to novel stimuli. This requires "a capacity to detect and generalize symmetry or asymmetry" (Giurfa, Eichmann and Menzel, 1996, p. 458). It was also shown experimentally that bees have an innate preference for symmetrical shapes, but this in no way undermines a mentalistic explanation of their performance. The existence of a pattern preference in honeybees does not explain how the concept "asymmetrical" is acquired, or how bees suddenly "figure out" what to look for in novel stimuli, after several trials. These facts can only be accounted for by supposing that the bees were trying to learn what they had to do in order to obtain their reward consistently, and finally managed to form a general concept of what the rewards had in common. The fact that trained bees tend to pay more attention to symmetrical rather than asymmetrical stimuli simply shows that they can form some concepts (e.g. "symmetrical") more easily than others ("asymmetrical"). For that matter, as Gould (2002, p. 44) points out, human infants display the same innate preference.

Other research has shown that bees can discriminate vertical from horizontal stripes, and apply this distinction to novel stimuli showing the same patterns. These experiments satisfy the standard requirements for categorisation: (i) a variety of stimuli sharing some common feature are rewarded, rather than an individual stimulus; and (ii) the animals can transfer the concept to novel stimuli (Menzel and Giurfa, 2001, p. 66).

S.23 An animal's ability to form categorical concepts and apply them to novel stimuli indicates the presence of mental processes - in particular, meta-learning.

Incidentally, I would suggest that there is a hidden bias in the search for conceptual learning, which has so far impeded our search for this kind of learning in "simpler" animals such as worms. From a cognitive perspective, a concept, properly speaking, is more than a mere category such as "red", which an animal could be neurally hard-wired to process. A cognitive concept requires an ability on the part of an individual to unify stimuli previously perceived as disparate. The kinds of stimuli most amenable to this kind of conceptualisation are visual and auditory stimuli. It is easy to see how different shapes can be grouped under a family concept (e.g. "triangular" or "symmetrical"). One can also classify sounds by their acoustic properties (e.g. "C" or "single note"). However, many invertebrates have a very weak capacity to discriminate between colours and sounds, and may therefore be unable to form most or all audiovisual concepts. The predominant sensory modality for these animals is usually smell. But how does one go about categorising smells? Although there are words in our language for individual smells, there are very few words that signify a common feature of disparate smells. ("Fragrant" and "rank" are two possible examples.) The whole notion of what a family of related smells is needs to be thought out carefully, before we can investigate the concept-forming abilities of animals (such as worms) whose sensory modality is predominantly olfactory rather than audiovisual.

The sudden improvement in performance noted by Gould in categorical tasks (2002, p. 44) suggests a useful experimental way of identifying the presence of insight in animals. Cognitive tasks for animals should be designed with the aim of eliciting this kind of "ah-ha" result.

Even more impressively, honeybees seem to be able to form highly abstract concepts such as "same" and "different", according to research by Giurfa, Zhang, Jenett, Menzel & Srinivasam (2001). A description of the experiments is given in the Appendix). Briefly, honey bees have been shown to be capable of delayed match-to-sample (DMS) learning, where an animal is shown an initial stimulus or sample, and then, after a delay, is required to choose from a range of stimuli, one of which is the same as the sample. Even though the sample is changed continually, the animals have to learn to always choose the stimulus that matches the sample, to obtain a reward. To perform the task it is necessary to acquire the rule that provides the goal of matching - "always choose the stimulus that is the same as the sample" - and it is also necessary to hold the information about the sample "in mind" to perform the test discrimination. Success in this task also presupposes sophisticated discrimination abilities in an insect and suggests the existence of an analogue of declarative memory (memory for facts). Honey bees have performed well in a range of DMS tasks, showing the ability to transfer their concept of "same" from one context (same colour) to another (same pattern of stripes) in successive trials, or vice versa (see Appendix).

One might attempt to account for the bees' DMS learning feats by positing that they are storing a "snapshot" of the sample in their memories, which elicits their response to a subsequent matching stimulus. On this account, the bees are not forming an abstract notion of "same", but simply matching pixels. However, the fact that bees can recognise and distinguish human letters, regardless of size, colour, position or font (Gould and Gould, 1988) refutes this "snapshot" hypothesis. Nor can such a hypothesis account for bees' abilities to identify general features of stimuli (e.g. asymmetry).

Even more impressively, honey bees are capable of solving a delayed non-matching to sample task, where they have to choose the stimulus that is different from the original sample (Giurfa, 2003).

The point that needs to be kept in mind here is that "sameness" and "difference" are not physical properties as such: they do not describe a measurable property of an object or group of objects. While one can describe what the bees are doing in a particular DMS task, using empirical terminology (e.g. the bees are looking for a stimulus whose colour matches the sample's), it is impossible to describe what the bees are doing in the ensemble of tasks, where they have to match colours or patterns, without employing abstract, non-empirical terminology (the bees are looking for a stimulus that is the same as the sample). The strategy for success in a DMS task has to be formulated at this level.

But why should a mind be needed to identify non-empirical properties? What I am proposing here is not that "non-empirical" equates to "mental", but that the identification of non-empirical properties is inherently mentalistic. Whereas empirical properties can be identified by some process of association and recall, non-empirical properties, such as sameness, have to be identified by looking for the rule which generates instantiations of these properties. The activity of attempting to follow a rule is a mentalistic one, as it can only be characterised in intentional terms.

S.24 An animal's ability to identify non-empirical properties is a sufficient condition for its having mental states (intentional acts). Such an animal can apply non-emprical concepts, by following a rule.

Does the ability of honey bees to solve DMS tasks mean that they have the mental concepts of "same" and "different"? I suggest that bees have a concept of sameness, without knowing what they have concepts of, and without knowing that they have a concept of sameness. The last two abilities, but not the first, presuppose the possession of a language which is capable of expressing abstract concepts. There are no indications that bees possess such a language. (The phenomenon of bee "language" will be discussed in chapter 4.) The distinctions I have invoked here reflect Dretske's (1995) distinctions between being conscious of something (e.g. burning toast), being conscious of what you are conscious of, and being conscious that you are conscious of it.

Is a bee's concept of "sameness" the same as ours? I propose that this question can be resolved if we consider the following three questions: (i) do bees make the same responses as we do in DMS tests?, (ii) do they make responses for the same range of objects as we do?, and (iii) do they make appropriate responses for all objects that are empirically accessible to them? The answer to the first two questions is obviously negative: (i) bees cannot make the same responses, as their discriminatory abilities are different from ours (e.g. their vision is poorer than ours), and (ii) there are certain kinds of objects of which bees are unaware, as they can only be apprehended through abstract language. The third and more substantial question relates to whether they have a general concept of an "object", which they can apply to all kinds of stimuli that they can sense. Can they, for instance, apply the concept of "sameness" to smells, or only to visual stimuli? (If the latter is the case, then bees' concept of "sameness" is indeed a lower-level one than ours, as its scope is limited to one sensory mode.) And can they apply their concept across sensory modes - e.g. can they compare a visual stimulus (e.g. a disk marked with red paint) with a smell (e.g. a disk with no marks, impregnated with the smell of eucalyptus) and judge them to be different?