Transitive inference by pigeons: does the geometric presentation of the stimuli make a difference?

Positional inference in rhesus macaques

Understanding how organisms make transitive inferences is critical to understanding their general ability to learn serial relationships. In this context, transitive inference (TI) can be understood as a specific heuristic that applies broadly to many different serial learning tasks, which have been the focus of hundreds of studies involving dozens of species. In the present study, monkeys learned the order of 7-item lists of photographic stimuli by trial and error, and were then tested on "derived" lists. These derived test lists combined stimuli from multiple training lists in ambiguous ways, sometimes changing their order relative to training. We found that subjects displayed strong preferences when presented with novel test pairs, even when those pairs were drawn from different training lists. These preferences were helpful when test pairs had an ordering congruent with their ranks during training, but yielded consistently below-chance performance when pairs had an incongruent order relative to training. This behavior can be explained by the joint contributions of transitive inference and another heuristic that we refer to as "positional inference." Positional inferences play a complementary role to transitive inferences in facilitating choices between novel pairs of stimuli. The theoretical framework that best explains both transitive and positional inferences is a spatial model that represents both the position of each stimulus and its uncertainty. A computational implementation of this framework yields accurate predictions about both correct responses and errors on derived lists.

Transitive inference in pigeons may result from differential tendencies to reject the test stimuli acquired during training

In the five-term, transitive inference task used with animals, pigeons are trained on four simultaneous discrimination premise pairs: A + B -, B + C -, C + D -, D + E -. Typically, when tested with the BD pair, most pigeons show a transitive inference effect, choosing B over D. Two non-inferential hypotheses have been proposed to account for this effect but neither has been reliably supported by research. Here we test a third non-inferential hypothesis that the preference for B arises because the animals have not had as much experience with B - in the A + B - discrimination as they have had with the D - in the C + D - discrimination. To test this hypothesis we trained the Experimental Group with the A + B - discrimination in which, over trials, there were four possible A + stimuli that could appear. This was done to encourage the pigeons to learn to reject the B - stimulus. For the Control Group there was only one A + stimulus over trials, as is typically the case. We also varied the nature of the stimuli between groups, such that colors served as the stimuli for half of the pigeons, whereas flags of different counties served as stimuli for the remaining pigeons. In both stimulus conditions, for the Experiment Group, we found little preference for stimulus B over stimulus D, whereas for the Control Group we found the typical preference for stimulus B. Thus, we propose that it is not necessary to attribute the transitive inference effect to an inferential process.