The present study was conducted to clarify the stimulus characteristics of the foraging environment which influence food-handling behavior in rats. Twenty-one female and 20 male rats were trained to search for a piece of food that was located at the end of the elevated straight alley. Rats' food-carrying behavior was observed on both covered and uncovered straight alley under conventional room light condition, followed by uncovered straight alley under reduced illumination over it. The results show that reduced illumination over the uncovered straight alley increase carrying small food in female rats and large food in male rats. These results were discussed in terms of the central place foraging (CPF) model (Lima, Valone, & Caraco, 1985) and the predatory imminence continuum (Fanselow & Lester, 1988).

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Formation of learning set and long-term memory in position recognition tasks of aged and young Japanese monkeys (Macaca fuscata) were studied. Four aged and three young monkeys were trained in an original position recognition task. Although all the monkeys learned this simple task, the aged monkeys needed more trials than the young ones. In six transfer tasks that followed, they experienced essentially the same position recognition task, but contextual cues, such as objects and the stimulus tray used, were changed across each transfer task. In the beginning of the transfer tasks, the young monkeys transferred their performance completely. In contrast, the performance of the aged monkeys declined because of the change. The ability to retain information in the aged monkeys was intact. Both the young and aged monkeys did not show any performance deficit even after a four-month retention interval, when the contextual cues were unchanged. These results suggest that learning in the aged monkeys was heavily dependent on the contextual cues, even if these cues were irrelevant in a task.

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Four groups of rats were trained in a straight runway to acquire two series of reward quantities (number of 45 mg food pellets). High item-discriminability condition (H condition) was presented with 8-10 and 2-0 (or 8-0 and 2-10) two-item series, whereas Low item-discriminability condition (L condition) was trained with 6-10 and 4-0 (or 6-0 and 4-10) series. During the inter-run interval, each rat in both conditions was kept in holding cages painted white or black, so that these brightness cues were also available as signals for the second item of their series. In the test phases, the brightness cues or the first items were altered between the series. Reversal of the brightness cues deteriorated anticipation of the second item in the L condition more than in the H condition, whereas the item reversal disturbed performance of the H condition more than that of the L condition. These results demonstrate that the extra-series brightness cue overshadows inter-item association, and that relative saliency of the cues determines degree of the overshadowing.

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