COLIN ALLEN

ANIMAL CONCEPTS REVISITED: THE USE OF SELF-MONITORING AS AN EMPIRICAL APPROACH

ABSTRACT. Many psychologists and philosophers believe that the close correlationbetween human language and human concepts makes the attribution of concepts to nonhu-man animals highly questionable. I argue for a three-part approach to attributing conceptsto animals. The approach goes beyond the usual discrimination tests by seeking evidencefor self-monitoring of discrimination errors. Such evidence can be collected without re-lying on language and, I argue, the capacity for error-detection can only be explainedby attributing a kind of internal representation that is reasonably identified as a concept.Thus I hope to have shown that worries about the empirical intractability of concepts inlanguageless animals are misplaced.

A pigeon, trained to peck for a food reward in response to pictures of trees,generalizes to new instances, responding appropriately to pictures that ithas never seen before (Herrnstein et al. 1976). Does it have a concept ofTREE? A pig, trained to respond to a pair of objects based on whetherthey are similar in shape and color, also generalizes to object pairs thatare new to it (Keddy-Hector et al. 1999). Does it have a concept of SAME-NESS? Many comparative psychologists consider it reasonable to attributeconcepts to nonhuman animals on the basis of such results. But questionsremain about the adequacy of such approaches to support conclusionsabout animal concepts.

Many of the skeptical arguments that have been put forward focus onthe relationship of language to human concepts. For example, Chater andHeyes (1994) argue that because nonhuman animals lack language it isnot possible to assign content to animal concepts in a rigorous way. Re-viewing theories of concept drawn from philosophy, cognitive psychology,comparative psychology, and cognitive ethology, Chater and Heyes arguethat none of the proposed theories can simultaneously satisfy the threedesiderata of (1) accounting for the close relationship between languageand concepts in humans, (2) being applicable to non-linguistic animals,and (3) being empirically tractable by behavioral methods. They conclude(p. 237) that “no clear sense has been provided for the claim that nonlin-guistic animals have concepts” and that “we simply do not know how toturn the claim that nonlinguistic animals have concepts into an empiricallysubstantive question”.

Erkenntnis51: 33–40, 1999.© 1999Kluwer Academic Publishers. Printed in the Netherlands.

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In the face of such criticism, should comparative psychologists and cog-nitive ethologists abandon the notion of animal concepts? There would becosts to doing so. First, insofar as cognitive psychologists have consideredconcepts central to their theories of human psychology, the abandonmentof animal concepts would make it harder to relate studies of animal cog-nition to attempts to understand the evolution of human concepts. Second,there is a very tight link between notions of concept and intentional con-tent. Concepts are constituents of the so-called intentional states (beliefs,desires, etc.): for instance, the thought that there is a squirrel in the tree isconstituted by a structured arrangement of the concepts of squirrel, tree,and in-ness. Giving up on the notion of animal concepts would make itdifficult (although perhaps not impossible) to see the form of a theory ofcontent for the intentional states of animals. Conversely, a workable theoryof animal concepts would be a significant contribution to the theory ofanimal intentionality generally.

Previously, Marc Hauser and I also disputed the adequacy of standardcomparative psychological results to support claims about concepts (Allenand Hauser 1991), but did not embrace the skeptical conclusion suggestedby Chater and Heyes. Rather, we undertook to provide suggestions for theempirical investigation of concepts in nonhuman animals. Specifically, wemaintained that the attribution of concepts is justified “if there is evidencesupporting the presence of a mental representation that is independent ofsolely perceptual information” and by means of a pair of thought exper-iments we indicated how we thought such evidence could be collected.Both of these thought experiments involved interpreting animals’ reactionsto perceptual evidence that would seem to indicate conflicting conclusions.Both of our thought experiments revolved around providing information toan individual organism that a familiar conspecific was not dead despite theappearance of death, and looking for changes in future reactions to sub-sequent presentation of the markers for death (or the absence of markersfor life).

The theoretical basis underlying the inference from these experimentsto claims about concepts was not carefully articulated in that 1991 paper.Instead we implicitly relied upon a comparative approach, which justifiedthe attribution of concepts to nonhuman animals by using human beha-vior in similar circumstances as the benchmark. It was not, however, ourintention to provide an account of animal concepts that was essentiallyanthropocentric for it was our belief that the basic strategy of using re-sponses to conflicting information as a basis for concept attribution couldstand alone. The present paper attempts to give a more explicit statement

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of the framework underlying this suggestion about empirical research intoanimal concepts.

Before turning to the substance of the proposal, it will be useful to makea distinction that is fundamental to any discussion of concepts, but that isoften neglected nonetheless. The distinction is marked in the questions“What is the (or our) concept of tree?” versus “What isFred’s conceptof tree?” which deal respectively with social and individual notions ofconcept. Whenever the idiom “the concept” is used, the definite articlesuggests that there is one concept which many individuals share (likewisefor “our concept”). But it is also common to hear it said that everyone has adifferent concept ofX. From the perspective of this claim about individualconcepts, it can seem unlikely that there should be such a thing as “the”concept of anything rather than just a collection of more or less related in-dividual concepts ofX. In commonsense psychology this tension betweensocial and individual conceptions of concept is mostly unanalyzed.

Both social and individual conceptions of concept are important toscientific psychology. Social concepts play a role in explaining commu-nication and cooperation among individuals, while individual concepts areimplicated in the structure of individual behavior and differences betweenthe behavior of individuals. Both conceptions also have intuitive counter-parts in animal psychology. For instance, assuming that it will be possibleto make sense of animal concepts, one might consider what concepts areimplicated in the alarm calling systems of a particular species, such as thevervet. As in human social groups, the group concept involves a centraliz-ing tendency: vervets communicate and cooperate with each other in waysthat tend to maintain a stable reference for specific alarm calls. Yet there isalso room for individual difference: some vervets may be more likely thanothers to distinguish between different species of raptor for the productionof their avian predator alarm calls, and this may not be simply a functionof differences in perception.

In scientific contexts (particularly cognitive psychology) where the fo-cus is ostensibly on individual concepts it is quite common to find theuse of idioms that are more suited to the social conception. Philosophicalarguments about animal cognition are also plagued by failure to heed thedistinction. For example, several philosophers have been tempted by theargument that animals do not have beliefs because they lack the constituentconcepts: for example, a dog does not believe there is a squirrel in the treebecause it lacks “the” (presumably the authors meanhuman) concept ofsquirrel. But there is no reason to think that having the belief requires thatanimals have that specific concept, nor that lacking the canonical concept

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of squirrel means that they lack any concept whatsoever (see Allen 1992,Allen and Bekoff 1997 for discussion).

The notion under discussion in this paper is that of the individual con-ception of concept. Of particular interest is the relationship between con-cepts and perception. Most, and perhaps all organisms are capable of cat-egorizing stimuli into perceptual equivalence classes – a basic require-ment for producing consistent responses to stimuli. But some organismsconstruct categorization schemes that, in a sense to be explained below,transcend particular perceptual stimuli. Concepts are the mental represen-tations constituting the nodes in such categorization schemes.

For example, consider the representation of death (Allen and Hauser1991). Many organisms have perceptual mechanisms whose function itis to allow them to respond differentially to dead or alive conspecifics.Ants, for example, respond to the presence of acidic byproducts of de-composition, allowing them to detect and remove dead conspecifics fromthe nest. Yet ants almost certainly have no concept of death; that is theyprovide no evidence of a capacity to represent death independently of theirperception of the chemical indicator. Thus, in this respect, they do nottranscend perceptual stimuli. This is indicated by the fact that ants willremove from the nest anything that has oleic acid painted on it, includingother live ants. Although the ants get other information that would tendto count against the assessment that the acid-treated conspecific is dead(they are for instance capable of detecting its motion), they are incapableof using this information to modify the removal response. While it is thebiological function of their chemosensors to detect dead conspecifics, thisdetection ability is merely perceptual not conceptual.

In contrast, humans can represent the status of an organism independ-ently of particular perceptual stimuli. A body that appears not to be breath-ing may nonetheless be judged to be alive, and one that appears to bebreathing may be judged dead. (There is an emphasis here on the word “ap-pears”.) Conceptual representation of death allows the organism to tran-scend any particular stimuli. This in turn facilitates more flexible behavior.The capacity to represent death independently of specific perceptual indic-ators allows the organism to learn new relationships between perceptualindicators and the underlying condition of being dead.

We are now in a position to see how one might overcome the objectionthat no empirical content can be given to the claim that a languagelesscreature possesses concepts: one seeks evidence for the non-perceptualrepresentations just mentioned. There may be several ways to do this,but here is one suggested schema for the investigation of concepts. An

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organism O may reasonably be attributed a concept ofX (e.g., TREE)whenever:

(i) O systematically discriminates someXs from some non-Xs; and(ii) O is capable of detecting some of its own discrimination errors between

Xs and non-Xs; and(iii) O is capable of learning to better discriminateXs from non-Xs as a

consequence of its capacity (ii).

It is important to be clear that the purpose of these three clauses is notto provide a philosophical analysis of what it is for an organism to possessa concept. The question of when it is reasonable to attribute a concept toan animal is a distinct question from that of what it means for an animal topossess a concept, just as the question of when it is reasonable to believethat someone is a murderer differs from the question of what it meansto be a murderer. Meeting conditions (i)–(iii) above may provide goodgrounds for attributing concepts to animals, even though these conditionsneed be neither necessary nor sufficient for concept possession, just asfinding a victim’s blood on a pair of socks may provide good grounds forbelieving the sock owner to be a murderer even though blood on sock isneither a necessary nor sufficient condition for being a murderer (Allen andBekoff 1997). To explain why satisfaction of the three conditions should beconsidered good evidence for concept possession in animals it is necessaryto say something about what it means to possess a concept, but much lessthan a full analysis needs to be provided.

Investigation of the capacities specified in clauses (i)–(iii) is empiric-ally tractable in languageless creatures. Satisfaction of clause (i) has beenextensively studied in animals by the kinds of experiments referred to inthe first paragraph of this paper. For instance, pigeons shown photographsof human faces interspersed with photographs of other items can be taughtto peck a response key only when a face is presented. The animals gen-eralize their categorization responses to new photographs containing facesthat were not seen during training. This shows that the discriminationsare systematic, not based on having learned piecemeal the particular re-sponse for each individual member of the set of training stimuli. Likewise,Keddy-Hector et al. (1999) show that pigs learned to respond differentiallyto stimuli consisting of a pair of objects, depending on whether the twoobjects differed in one of the properties of shape, size, or color, or whetherthey were identical in those respects, and that the pigs generalized thediscrimination of sameness and difference to novel pairs of familiar objectsand to pairs of novel objects. Although the same/different categorization isof an abstract relationship between perceptual properties, the discrimina-tion still remains tied to perception in the sense that we have no evidence

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that these animals can judge that two things are really the same despiteappearing different, or vice versa. Thus these discoveries satisfy clause (i)of the schema but not either of the other clauses.

The capacities specified in clauses (ii) and (iii) have not been extens-ively investigated, but in combination they provide a basis for empiricalinvestigation that allows us to resist the pessimistic conclusion drawn byChater and Heyes. By helping to determine the boundaries of the animals’representations, the joint investigation of capacities (ii) and (iii) can helpto settle questions about the content of the representations. Clause (ii) con-cerns detection of error. There are various ways that an animal might beinformed by an external cue that it has miscategorized something, but insuch cases there is a challenge to any empirical inference because of thepossibility that the cue indicating the error is sufficient alone to explainany subsequent behavior by an animal. (It is rather like the chemical cuebeing sufficient alone to explain why ants remove dead conspecifics – nocognitive representation of death is required.)

It is, however, possible for animals to show evidence of error detec-tion without external cuing, i.e., they can show self-monitoring of theirperformance. Pigs again illustrate the point, although in this example it isknowledge of response error rather than perceptual error that is demon-strated. Pigs trained on the same/different task just described would stilloccasionally make errors (wrong choices) while performing at an overallrate at or near 90% correct. After committing to a response but beforeany feedback was provided, some pigs would attempt to back away fromthe choice they had made. Analysis of 22 cases of the backout behaviorshowed that only one of these cases occurred after the pig made a correctchoice (Keddy-Hector et al. 1999). It is intriguing to try to account for thisbehavior, but regardless of what it shows in this particular experimentalset up, it indicates that under certain conditions some animals can providenon-linguistic evidence that supports the attribution of endogenous errordetection capacity.

Clause (iii) is the most difficult to articulate and defend. Indeed, someparticipants at workshops based on the ideas in this paper were satisfiedthat concepts are reasonably attributed on the basis of the other clauses.Some were satisfied with (i) alone (and some prefer other criteria – thoseare fine for the point here is not to provide either necessary or jointlysufficient conditions for concept possession). It is my view, however, thatclause (iii), when satisfied, provides a stronger case for the attribution ofconcepts because it provides a link between the first two capacities. If thecapacity to satisfy (ii) is causally responsible for better performance on (i)then we have evidence that there is an integrated processing mechanism

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linking perceptual categorization and the recognition of perceptual error,and hence a representation system that compares the perceptual contentwith an independent representation of what the perception is supposed torepresent, i.e., a concept.

The internal states implicated in the explanation of these capacities areworthy of being designated as concepts. For these capacities to be imple-mented it appears that there must be an internal standard of comparisonthat represents the organism’s world independently of its perceptual rep-resentation at any given moment. Thus, such evidence supports the claimthat organisms with these capacities possess representations of the worldthat are detached from immediate perceptual information.

The difference between perceptual representations and concepts corres-pond to longstanding philosophical ideas about concepts (Watson 1995).Descartes, for example, discusses the power of the mind to represent achiliagon even though the visual presentation of such an object would beindistinguishable from that of a 999-sided figure. Among cognitive psy-chologists too, the major current theories of concepts are all concernedwith the way in which concepts serve to unite varied perceptual presenta-tions of instances.

The close connection of language to concepts in humans has seducedmany into thinking that the two notions of language and concept cannotbe disentangled. This close connection may be explained on the currentschema in virtue of the fact that languages provide a structure that has avast number of degrees of freedom with respect to immediate perception.Linguistic representation is, then, the basis for the most fine-grained sys-tem of conceptual representation that we know. But it would be a mistaketo think that it is the only basis for conceptual representation available. Itis well within the bounds of possibility that other species have ways ofstructuring their experiences that transcend merely grouping those exper-iences into equivalence classes for the purposes of producing immediatebehavioral responses. Such a capacity contains the rudiments of a con-ceptual scheme. Thus, I argue, there is a clear sense for the claim in whichlanguageless animals might possess concepts, and we do know how to turnthis claim into an empirically substantive question.

REFERENCES

Allen, C.: 1992, ‘Mental Content’,British Journal for the Philosophy of Science43, 537–553.

Allen, C. and Bekoff, M.: 1997,Species of Mind: The Philosophy and Biology of CognitiveEthology. MIT Press, Cambridge, Massachusetts.

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Allen, C. and Hauser, M. D.: 1991, ‘Concept Attribution in Nonhuman Animals: Theoret-ical and Methodological Problems in Ascribing Complex Mental Processes’,Philosophyof Science58, 221–240.

Chater, N. and Heyes, C. M.: 1994, ‘Animal Concepts: Content and Discontent’,Mind andLanguage9, 209–246.

Herrnstein, R. J., Loveland, D. H. and Cable, C.: 1976, ‘Natural Concepts in Pigeons’,Journal of Experimental Psychology, Animal Behavior Processes2, 385–302.

Keddy-Hector, A., Allen, C. and Friend, T. H.: 1999,Cognition in Domestic Pigs:Relational Concepts and Error Recognition(submitted).

Watson, R. A.: 1995,Representational Ideas: From Plato to Patricia Churchland. Kluwer,Dordrecht, the Netherlands.

Department of Philosophy, Texas A & M UniversityCollege Station, TX 77843-4237U.S.A.e-mail: colin.allen@tamu.edu