significantly better than would have been expected by chance. This suggested that a non-human subject had in fact demonstrated stimulus equivalence following training on AB and BC conditional relations.
Kastak and Schusterman (1993) showed that California sea-lions could transfer identity match-to-sample performance to novel visual stimuli. This study by Schusterman and Kastak (1993) extended this finding to examine the ability of a sea-lion to form concepts of symmetiy and transitivity following conditional discrimination training. On the initial BA syimnetiy test, Rio’s performance failed to reach criterion, a finding which was consistent with previous studies of
symmetiy with non-humans. Sidman et al (1982) failed to demonstrate symmetry with non-humans, and they suggested that providing enough examples might facilitate the emergence of symmetry with non-humans. The data form Schusterman and Kastak seems to support this suggestion. Schusterman and Kastak state "We believe the critical factor in Rio's subsequent performance in passing tests of symmetry, transitivity and equivalence stems directly from her experiencing enough exemplars to group these interrelated concepts" (p.836). A study by Wright, Cook, Rivera, Sands and Delius (1988) had also shown multiple exemplar training to be helpful in acquisition of identity relations with pigeons. It also seems likely that the simple-to-complex training and test protocol was helpful in establishing equivalence performance by ensuring establishment of all the pre requisite repertoires.
Hayes (1989) had suggested that it might be harder to show derived symmetiy with a non-human than to show derived transitivity. Symmetiy requires a bi-directional stimulus-stimulus relation while transitivity only requires a uni-directional
stimulus-stimulus relation although transitivity does require the co-ordination of two terms by means of a third, linking term. In this case, it may be easier to
demonstrate accurate non-human performance on a task based on transitivity rather than symmetry. For this reason , experiments on transitive inference tasks using non-human subjects may be helpful in considering the range of animal cognition. Like equivalence, transitive inference requires the derivation of new relations on the basis of previously learned relations, but given Hayes' (1989) comments it would be expected that it would be easier for non-humans to demonstrate derived relations on a task of this sort.
Chapter 3: Coalition in Non-Humans 43
Transitive Inference
Transitive inference provided a useful way to explore the limits of non-human cognition. Higa and Staddon (1993) suggested that there has been a tendency by cognitive psychologists to treat humans as isolated subjects and ignore
comparisons between human and non-human abilities. They believed that this isolated approach was mistaken and that transitive inference provided a way to "study" the conditions under which behaviour that in humans would be symbolic can be brought about, by non-verbal means in other animals" (p.265). McGonigle and Chalmers (1977) also believed that the transitive inference task could be of use to comparative psychology. They pointed out that monkeys seemed able to learn complex tasks but it was not clear if they could reason. One problem was that the reasoning tests used tended to be very verbally dependent and "it is difficult to devise tests which are both meaningful to non-verbal subjects yet satisfy the stringent requirements of a formal reasoning test" (p.694). These formal reasoning tests tended to be very like those used by Burt, and later Piaget:
1. Edith is fairer than Suzanne 2. Edith is darker than Lili
3. Who is the darkest, Edith, Suzanne or Lili ?. (Burt 1919)
However, a transitive inference test for non-humans became possible following work by Biyant and Trabasso (1971).
Bryant and Trabasso (1971)
Piaget had suggested that children could not form transitive inferences until the age of about seven, when they reached the stage of concrete operations. Bryant and Trabasso suggested that children much younger than seven could in fact make transitive inferences provided they understood, and could remember the items of information they were being asked to combine. Bryant and Trabasso therefore suggested a simpler way of presenting the relational information the children had to combine in order to make a transitive inference. They taught the children a series of four overlapping pair discriminations, A>B, B>C, C>D, D>E, and then presented the test pair BD. By combining B>C and C>D the children could then infer B>D, even though the relation between these two stimuli had never been directly stated. The series of five stimuli were necessary in order to control for absolute
responding. If a three stimulus series had been used, A>B, B>C, the subject could respond correctly to A rather than C without making a transitive inference just because responses to A are always correct and responses to C are never correct. Using a five term series, A>B>C>D>E, prevents this as the stimuli in the critical