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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 20, Issue 4, 2007


Temporal Organization of Eating in Low- and High- Saccharin-Consuming Rats

When, where, and how much animals eat are influenced by food scarcity and risk of predation. The present study concerned the mediation of risk-related feeding patterns by emotion. Occidental Lowsaccharin- consuming (LoS) and High-saccharin-consuming (HiS) rats, which differ in both ingestion and emotionality, were studied in three steady-state paradigms: an “open economy” procedure (discrete session cyclic-ratio operant schedule) and two “closed economy” procedures (meal patterning, free feeding with running wheel access). Cyclic-ratio performance showed better defense of stable food intake against variable cost among LoS rats. In closed economies, LoS rats consumed a larger number of smaller meals and showed a more pronounced circadian rhythm in meal initiation and running than HiS rats. Taste finickiness appears to serve as a marker for heightened cross-modal risk reactivity, the expressions of which include tighter behavioral regulation of eating in conditions of scarcity and exaggerated nocturnality.

The Role of Visual Cues in the Comprehension of the Human Pointing Signals in Dogs

In this study we examined the effect of the visually emphasized pointing arm in the case of the “Cross-forward pointing” gesture in dogs which proved to be difficult for them in an earlier study (Lakatos, Soproni, Dóka, & Miklósi, 2008). Our hypothesis was that if we emphasize the directionality of the visual cue using different, more contrasting coloured clothes during the tests, the dogs will be able to enhance their performance in two-way choice tasks. Our results showed that the conspicuousness of the pointing signal can affect how dogs perceive it. In contrast to our initial hypothesis pointing in a long white sleeve on a black background did not increase the dogs’ performance, while the black sleeves with nude (“white”) hands had an enhancing effect. This suggests that dogs need to see a salient body part what overhangs the median of the body silhouette and when the whole body is covered by black colour then the nude (pointing) hand appears as a conspicuous asymmetrical feature on one side of the body. Making the pointing hand less conspicuous makes the effect invariably disappear. Thus in summary we assume that the key aspect of the pointing gesture is not the directionality but the visually asymmetric cue provided by the human informant.

A Comparative Analysis of the Preference for Dark Environments in Five Teleosts

The present article tried to establish dark/light preference in five different species of teleosts. We proposed, using the data obtained with this method in zebrafishes (Danio rerio), Cardinal-tetras (Paracheirodon axelrodi), lambaris (Astyanax altiparanae), Nile tilapias (Oreochromis niloticus), guppies (Poecilia reticulata) and banded-knife fishes (Gymnotus carapo), that preference for dark environments is a reliable and low-cost index of anxiety/fear in those species. A scototactic pattern of exploration was found in all species, and the pattern of locomotion in the white environment suggests its aversiveness for those species, with the exception of G. carapo and O. niloticus. A comparative analysis uncovered species differences in approach-avoidance dimensions of the task. The data are discussed in terms of the behavioral ecology of the animals and prey-predator relationships, suggesting a link with predator defense strategies in teleost.

A Brief Report: The Use of Experimenter-Given Cues by South American Sea Lions

South American sea lions (Otaria byrona) were tested in an object choice task in which they had to use one of the following experimenter-given cues to choose the correct object for a reward: (1) the experimenter pointed and gazed at the object, (2) the experimenter pointed at the object, (3) the experimenter gazed at the object, (4) the experimenter placed a marker on the object, or (5) the experimenter presented a replica of the target object. The sea lions were able to successfully use three of these five cues. These results demonstrate that relatively little experience with human trainers was necessary for the subjects to perceive and act on select attentional cues given by a human experimenter. These results indicate that sea lions are able to interpret certain untrained communicative cues successfully.