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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 11, Issue 4, 1998

Research Article

Water Retrieval by Norway Rats: Behavior as Deduction

The origin of behavior consistent with effective ("optimal") policies is an important topic in behavioral biology. In many cases, novel behavior patterns that emerge in unfamiliar situations are based on "trial and error" learning guided by rewards and punishments. The present work shows how an appropriate novel response canemerge full-blown in response to new contingencies if the situation has generic featuresthat can be recognized. This work is concerned with object retrieval, i.e., carriage of valued objects to a place of safety by Norway rats (Rattus norvegicus (Berkenhout); Rodentia: Muridae). Experiment 1 shows that selective retrieval of objects containing water over dry objects of the same material can occur immediately when rats are made thirsty; it is unlikely that this is a specific adaptation, since the opportunity to retrieve water in this way would rarely arise under natural conditions. Experiment 2 shows that without initial exposure to both objects under ad lib conditions (where the retrieval preference was for the dry objects), a process of trial and error is apparent as thirsty rats learn to select the appropriate object. It is argued that if object retrieval behavior is linked to a generic incentive feature and features such as wetness are receded into this general term, then appropriate object retrieval can be generated by a kind of deductive process. This type of generalist strategy would appear to be highly adaptive, in part because the usual tradeoffs between specialist and generalist strategies may not apply.

Contextual Discrimination After Nonreinforced Preexposure to the Context

Rats were trained on a contextual discrimination after nonreinforced

preexposure to both contexts. In Experiment 1, where contexts differed in terms of

tactile and visual stimuli, preexposure retarded subsequent discrimination by

comparison with non preexposed controls (latent inhibition). In Experiment 2, where

contexts differed only in terms of visual cue, discrimination was facilitated in

preexposed animals (perceptual learning). Food was used as reinforcer and anticipatory

activity as dependent measure. These results suggest that contextual similarity

influences the outcome of nonreinforced preexposure.

Left Hand Advantage for Prey Capture in the Galago (Galago Moholi)

Efficiency of hand use in nonhuman primates is often difficult to assess because of the relatively small number of responses made with a nonpreferred hand. The present study compared measures of reach efficiency in 8 galagos (Galago moholi), 4 left-hand preferent and 4 right-hand preferent subjects, tested in a reach apparatusdesigned to elicit equal numbers of responses by the left and right hands. The effect of variant or invariant target placement within sessions was also assessed by the use of both blocked and randomized trials. Efficiency was defined in terms of the percentage of successful reaches and the average duration of time required for reach execution. There was no effect of target variance on strength of hand preference or on either measure of performance efficiency. Preferred and nonpreferred hands did not differ with respect to these two measures. There was also no difference in the percentage of successful reaches between the left and right hands. However, for 7 of 8 subjects the left hand generated faster reach times than did the right hand, regardless of hand preference. The greater execufion speed with the left arm/hand is interpreted as exemplifying a lateralized neural advantage for the execution of ballistic reaching in galago species. The highly consistent timing of this prey capture behavior in the galago supports the view that this arm/hand movement is ballistic in type.