Abstract: Animals' abilities to use internal representations of absent objects to guide adaptive behavior and acquire new information, and to represent multiple spatial, temporal, and object properties of complex events and event sequences, may underlie many aspects of human perception, memory, and symbolic thought. In this review, two classes of simple associative learning tasks that address these core cognitive capacities are discussed. The first set, including reinforcer revaluation and mediated learning procedures, address the power of Pavlovian conditioned stimuli to gain access, through learning, to representations of upcoming events. The second set of investigations concern the construction of complex stimulus representations, as illustrated in studies of contextual learning, the conjunction of explicit stimulus elements in configural learning procedures, and recent studies of episodic-like memory. The importance of identifying both cognitive process and brain system bases of performance in animal models is emphasized.

Abstract: In this research, we asked whether 2 chimpanzee (Pan troglodytes) subjects could reliably sum across pairs of quantities to select the greater total. Subjects were allowed to choose between two trays of chocolates. Each tray contained two food wells. To select the tray containing the greater number of chocolates, it was necessary to sum the contents of the food wells on each tray. In experiments where food wells contained from zero to four chocolates, the chimpanzees chose the greater value of the summed wells on more than 90% of the trials. In the final experiment, the maximum number of chocolates assigned to a food well was increased to five. Choice of the tray containing the greater sum still remained above 90%. In all experiments, subjects reliably chose the greater sum, even though on many trials a food well on the “incorrect” tray held more chocolates than either single well on the “correct” tray. It was concluded that without any known ability to count, these chimpanzees used some process of summation to combine spatially separated quantities. Speculation regarding the basis for summation includes consideration of perceptual fusion of pairs of quantities and subitization.

Abstract: Four experiments used a four-choice discrimination learning paradigm to explore the pigeon's recognition of line drawings of four objects (an airplane, a chair, a desk lamp, and a flashlight) that were rotated in depth. The pigeons reliably generalized discriminative responding to pictorial stimuli over all untrained depth rotations, despite the bird's having been trained at only a single depth orientation. These generalization gradients closely resembled those found in prior research that used other stimulus dimensions. Increasing the number of different vantage points in the training set from one to three broadened the range of generalized testing performance, with wider spacing of the training orientations more effectively broadening generalized responding. Template and geon theories of visual recognition are applied to these empirical results.

Abstract: Three rhesus monkeys (Macaca mulatta) were trained to respond to exemplars of 1, 2, 3, and 4 in an ascending, descending, or a nonmonotonic numerical order (1-->2-->3-->4, 4-->3-->2--1, 3-->1-->4-->2). The monkeys were then tested on their ability to order pairs of the novel numerosities 5-9. In Experiment 1, all 3 monkeys ordered novel exemplars of the numerosities 1-4 in ascending or descending order. The attempt to train a nonmonotonic order (3-->1-->4-->2) failed. In Experiment 2A, the 2 monkeys who learned the ascending numerical rule ordered pairs of the novel numerosities 5-9 on unreinforced trials. The monkey who learned the descending numerical rule failed to extrapolate the descending rule to new numerosities. In Experiment 2B all 3 monkeys ordered novel exemplars of pairs of the numerosities 5-9. Accuracy and latency of responding revealed distance and magnitude effects analogous to previous findings with human participants (R. S. Moyer & T. K. Landaeur, 1967). Collectively these studies show that monkeys represent the numerosities 1-9 on at least an ordinal scale.

Abstract: Pigeons were trained to search for hidden food in a rectangular environment designed to eliminate any external cues. Following training, the authors administered unreinforced test trials in which the geometric properties of the apparatus were manipulated. During tests that preserved the relative geometry but altered the absolute geometry of the environment, the pigeons continued to choose the geometrically correct corners, indicating that they encoded the relative geometry of the enclosure. When tested in a square enclosure, which distorted both the absolute and relative geometry, the pigeons randomly chose among the 4 corners, indicating that their choices were not based on cues external to the apparatus. This study provides new insight into how metric properties of an environment are encoded by pigeons.