Skip to main content
Open Access Publications from the University of California


The International Journal of Comparative Psychology is sponsored by the International Society for Comparative Psychology. It is a peer-reviewed open-access digital journal that publishes studies on the evolution and development of behavior in all animal species. It accepts research articles and reviews, letters and audiovisual submissions.

Volume 15, Issue 4, 2002


Can Orangutans and Gorillas Acquire Concepts for Social Relationships?

Two orangutans’ and one gorilla’s understanding of social relationships was investigated using twodimensional photographs displayed on a touch-screen monitor. Unlike the photos used in similar studies, the photos presented here were not of exclusively familiar or related individuals, thus eliminating the use of previously learned associations or “genetic” similarities as cues. In Experiment 1, the subjects discriminated photos of mother-offspring pairs from photographs depicting other social relationships (siblings, unrelated group mates, mated pairs). In Experiment 2, they matched photos of mother-offspring pairs, mated pairs, siblings and groups of animals in a delayed matchingto- sample task (DMTS). In Experiment 3, they matched photographs depicting various behaviors (sleeping, eating, playing and grooming) in another DMTS procedure. Performance was significantly above chance in all three experiments, suggesting that both species of Great Ape might be sensitive to abstract concepts such as social relationships and activities.

A Training Program for Filter-Search Mine Detection Dogs

REST (Remote Explosives Scent Tracing) is an odor detection concept in which air from suspect locations is vacuumed though a polyvinyl chloride (PVC) netting filter. The filters are transferred to dogs trained to signal specific target odors such as drugs or explosives. Application for the detection of landmines involves vacuuming an area of land suspected to contain mines, and requires that the dogs achieve detection skills for very low concentrations of the target odor. Here, we describe the principles behind and results of a training program designed to produce REST dogs with detection skills similar to those obtained on filters from minefields. The entire training process for four dogs took under 6 months, and involved two trainers working for 1-5 days/week for about 5 h/day (dogs were trained most days, but both trainers were not always present). Principles underlying the training program were: (1) minimise dependency on handler, (2) encourage independent search, (3) build extended search by progressively reducing the frequency of occurrence of positive filters (using variable interval reinforcement), and (4) progressively generalise discrimination to lower concentrations of TNT. Reward-based “clicker” training was used exclusively. After 15 weeks, the dogs achieved 95% detection reliability. Properly documented training programs such as this one are essential if the industry is to further develop the REST concept for operational implementation on a broad scale.

A Species Difference in Visuospatial Memory in Adult Humans and Rhesus Monkeys: The Concentration Game

One of the most familiar children’s games (marketed under many names including the memory game, Concentration, and Husker Du also would seem to provide an excellent test of visuospatial memory. A computerized version of this game was written in which human adults or rhesus monkeys were required to find matching pairs of pictures by “flipping over” computer-generated images of cards. Finding one of the 2 to 6 pairs of images (color patches, line drawings, letters, etc.) caused the pictures to remain visible, but errors (mismatches) caused the images to be concealed again and thus required the participants to remember which images had been seen and where each was hidden. In a series of experiments, all participants were able to locate the pairs of stimuli, but monkeys were consistently and significantly worse than the human adults. Indeed, the monkeys frequently perseverated on errors, causing them to be worse than chance in many conditions, even after training. In the present manuscript, data are presented to suggest that this species difference does not simply reflect a limitation on the monkeys’ knowledge of the “rules of the game.”

Sequential Pattern of Behavior in the Common Palm Civet, Paradoxurus hermaphroditus (Pallas)

Animals possess a behavioral repertoire, which forms the basis of activity patterns. In the present investigation, the behavioral sequences of seven palm civets were observed in captivity during 18:00- 06:00 h. The transitions from one behavioral state to another were revealed using a contingency table representing the six behavioral states viz ., resting, feeding, comfort behavior, social behavior, sniffing behavior and locomotion. The behavior sequences were elucidated using a first order Markov chain model. The hypothesis for the first order Markov chain model against a zero order chain is sustaining in palm civets and the probability of the animal being in a particular state depends on the immediately preceding act and all other past history is immaterial.

Simultaneous Pattern Discriminations by Pigeons Reveal Absence of Mirror-Image and Left-Right Confusions

In a simultaneous discrimination task, pigeons were first trained with two patterns: one rewarding (A+) and the other unrewarding (B-) that contained the same components (the symbols: c, d, ■ and <) but displayed in a different spatial layout. They were then tested for their choices of patterns: (1) A+ vs. its mirror image (MI); (2) A+ vs. its left-right reversal (LR); (3) MI vs. other layouts (OL) of the symbols; (4) LR vs. OL. In the first two conditions, A+ was chosen over its MI and LR reversal (i.e., no MI or LR confusions were found). In the last two conditions, MI and LR were not chosen over the OL, that is, they were not treated as substitutes for the A+. On the contrary, the OL stimuli were chosen over the transformations of A+. In all cases, the discriminations revealed a failure to confuse the A+ with its transformations, as predicted from work showing that the position of pattern components is important in pattern recognition.