TRANSITIVE RESPONDING IN ANIMALS AND HUMANS - EXAPTATION RATHER THAN ADAPTATION

In order to survive and reproduce, individual animals need to navigate through a multidimensional utility landscape in a near-optimal way. T here is little doubt that the behaviourally more advanced species can bring cognitive competencies to bear on this difficult task. Among the cognitive abilities that are helpful in this context is transitive in ference. This is typically the competency to derive the conclusion B > D from the premises A > B, B > C, C > D and D > E that imply the seri es A > B > C > D > E. In transitive inference tests used with humans, the letters stand for verbal items and the inequality symbols stand fo r a relational expression. To investigate analogous competencies in no n-human animals a non-verbal form of the task is used. The premise pai rs are converted into a multiple instrumental discrimination task A+B- , B+C-, C+D- and D+E-, where the letters stand for non-verbal stimuli and the plus and minus symbols indicate that choices of the correspond ing stimuli either lead to a reward or to a penalty. When these traini ng pairs are adequately discriminated, transitive responding is tested with intermittent presentations of the novel pair B degrees D degrees , where the circles indicate that responses to the stimuli are not rei nforced. Using variants of this basic conditioning task it has been sh own that pigeons, rats, squirrel-monkeys, macaques, chimpanzees, young children, older children and adult humans commonly reveal transitive preferences for B over D. Several theories have been proposed to expla in this transitive behaviour. The evidence supporting these various mo dels is reviewed. It is shown that the learning of the premises normal ly brings about a choice and reinforcement biasing and balancing proce ss that can account for transitive responding. It is argued that a ver y simple algebraic learning model can satisfactorily simulate many of the results obtained in transitivity experiments, including some produ ced by human subjects who in principle, could have been applying ratio nal logical rules. It is demonstrated that a value transfer mechanism also assumed to explain transitive responding, is in fact, a real phen omenon based on classical conditioning. However, it is argued that it mostly plays a minor role in transitive responding. It is shown that t he algebraic learning model can be easily converted into a neural netw ork model exhibiting an equivalent performance. The model can also be modified to cope with the surprising finding that a proportion of huma n individuals and a few animals subjects learn to discriminate the pre mise pairs, but nevertheless fail to respond transitively to the concl usion pair. This modification can simulate the results of experiments using non-linear, in particular circular, relational structures. The e volution of transitive responding is considered within the framework o f ecosocial demands and neurobiological constraints. It is concluded t hat, in agreement with a preadaptation (exaptation) evolutionary origi n, it seems to involve little beyond the capacity to learn multiple st imulus discriminations. (C) 1998 Elsevier Science B.V.