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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 23, Issue 2, 2010

Research Paper

Targets and Tactics of Play Fighting: Competitive versus Cooperative Styles of Play in Japanese and Tonkean Macaques

Macaques are the most geographically widespread and behaviorally diverse primate genus, and although macaque species share the same, basic social structure, they display broad inter specificvariation in patterns of adult social behavior. Based on these patterns, macaque species have been arranged along a 4-grade scale for social style. At one end of the scale, there are grade 1 species (e.g., Japanese macaques) that have highly hierarchical and despotic social systems, and at the other end, grade 4 species (e.g., Tonkean macaques) that have more relaxed and egalitarian social systems. We predicted that a species from the more despotic end of the spectrum should have more competitive play fights and that a species from the egalitarian end, more cooperative ones. A detailed analysis of videotaped sequences of juvenile play fighting in Tonkean and Japanese macaques was used to characterize the targets and tactics of attack and defense. Even though the two species have a similar behavioral repertoire, there are significant differences in how that repertoire is used and these differences are consistent with one species having more competitive interactions than the other. Contrasting multi-animal play fights versus pairs showed that the more cooperative style of the Tonkean macaques is further exaggerated. The results suggest that differences in styles of attack anddefense in play fighting may be influenced by differences in the species’ social systems.

Learning About Absent Outcome in the Presence of Conditioned Excitor and Inhibitor: A Study Using Conditioned Flavor Preference

We examined whether aversive conditioning of a previously established conditioned inhibitor (A) for sucrose solution (X) affects subsequent consumption and aversive conditioning of X. Experiment 1 established an appetitive conditioned inhibition procedure in which odor A became a conditioned inhibitor for X. In Phase 1 of Experiments 2 and 3, subjects received either inhibitory (Group INH: AB/BX/C) or excitatory conditioning of A (Group EXC: ABX/B/C), or a control treatment (GroupCONT: AB/B/CX). In Phase 2, A was paired with an injection of lithium chloride (LiCl) and consumption of X was measured. X was paired with LiCl in Phase 3, and tested in extinction. After a moderate amount of Phase 1 treatment in Experiment 2, animals in Group EXC showed a reduction in consumption of X after A-LiCl pairings, while those in both Groups EXC and INH rapidly acquired an aversion to X during X-LiCl conditioning. However, when extended Phase 1 treatment was given in Experiment 3, animals in Group INH tended to acquire the aversion to X at a slower rate than those in Group CONT. Animals in Group EXC did not show any superiority in acquisition of theX aversion. The results are discussed in terms of mediation processes by event representations.

A New Change-of-Contents False Belief Test: Children and Chimpanzees Compared

In the handful of existing comparative false belief studies, chimpanzees have consistently failed tests that 5- to 6-year-old children have passed. However, those tests were either explicitly cooperative communicativeor competitive, both of which are problematic for different reasons. We therefore devised a new change-of-contents false belief test for children and chimpanzees that did not include these problematic elements. Nevertheless, chimpanzees showed no evidence of understanding false beliefs (consistent with past research, however, children showed a clear improvement in test performance from 3.5 to 4.5 years of age). Our results suggest that the cooperative-communicative or competitive nature of previous false belief tests was not solely responsible for chimpanzees’ failure. That chimpanzees have now also failed a more socially neutral test supports the conclusion that chimpanzees may simply not recognize false belief states in others. Additionally, our test departs from a near exclusive reliance on the change-of-location paradigm in false belief research. It therefore expands the repertoire of methods available for testing false belief understanding with minimally verbal and nonverbal procedures.

Domesticated Dogs’ (Canis familiaris) Response to Dishonest Human Points

Pointing is a conventional communicative gesture used by humans to direct others’ attention to an environmental feature. Several researchers have argued that pointing becomes so ingrained for humans from a young age that children often have difficulty interpreting the gesture in a novel way. Recent research suggests domestic dogs are also sensitive to human gestures (including points) and proficient in recognizing and acting on humans’ visual attention. We explored the role of pointing indogs’ choice behavior and whether dogs, like human children, have difficulty interpreting the gesture novelly. In Experiment 1, we explored whether dogs would differentially follow a static human point when it was administered by a familiar or unfamiliar individual and that individual indicated or failed to indicate the correct location of a food reward. The results indicated dogs chose the container specified by the demonstrators’ point in the honest and dishonest condition. Demonstrator familiarity did not alter performance. In Experiment 2, we compared dogs’ propensity to follow a static point versus other cues (momentary point, standing location) when the cue never indicated the correct location of a food reward, which was either visible or hidden during choice. The results suggested dogs did not inhibit their approach to a location indicated by a deceptive static point even when thelocation of a reward was visibly available during choice. However, dogs used a deceptive momentary point or standing location to locate food in both visible and hidden trials. In Experiment 3, we explored if dogs could overcome their tendency to follow a deceptive static point. These results indicated dogs learned to inhibit their approach to a deceptive static point when the reward was visible during choice. However, when information about the reward’s location was later hidden, dogs reverted to following the demonstrator’s static point.

A Brief Report: Capture Order is Repeatable in Chickadees

Black-capped (Poecile atricapillus) and mountain chickadees (Poecile gambeli) have been used as amodel to examine cognitive functions including perception, episodic-like memory, and spatiallearning and orientation. Recently, these species have been used in two studies to examine therelationship between learning and novel environment exploration and novel environment explorationand dominance. In the current study we explored whether these two species show consistency inbehavior over time. In same species/same sex groups, male and female black-capped and mountainchickadees were released into a room and then captured by an experimenter with the procedurerepeated one week later. Males, but not females in both species show consistency in capture orderover both sessions. We discuss implications of this finding in the context of possible sampling biases.