Pigeons chose between 50% and 100% reinforcement on a discrete-trials concurrent-chains procedure with fixed-ratio 1 initial links and fixed-time terminal links. The 100% alternative always provided food after a terminal-link delay, whereas the 50% alternative provided food or blackout equally often after a delay. Additionally, the terminal-link stimuli on the 50% alternative were correlated with the outcomes in signaled, but not in unsignaled, conditions. The effects of intertrial-interval duration and length of the terminal-link delays on choice of the 50% alternative were investigated in four experiments. Preference for the 50% alternative varied with signal condition and duration of the terminal link leading to food, but not with duration of either intertrial interval or the terminal link leading to a blackout. The results are discussed in terms of conditioned-reinforcement effects, Mazur's hyperbolic-decay model, and delay reduction.

No abstract

Pigeons obtained food by pecking at an unmarked target location on a video screen equipped with a touch-sensitive frame. The target area was located near the top edge of the screen in Experiment 1 and near the left edge of the screen in Experiment 2. On baseline trials, a graphic landmark was located below and left of the target (Experiment 1) or below and right of the target (Experiment 2). In both experiments, baseline search distributions showed a single peak and were roughly symmetrical about the target area in both horizontal and vertical dimensions. On occasional test trials, the landmark was shifted horizontally, vertically, or diagonally by 1.5 em or 3 em. In both experiments, landmark shifts in the dimension parallel to the nearest edge produced systematic shifts in the peak place of search. Landmark shifts in the dimension perpendicular to the nearest edge produced inconsistent (Experiment 1) or relatively small (Experiment 2) shifts in peak place. The magnitude of the behavioral shift was always less than the magnitude of the landmark shift and was not consistently greater when the landmark was shifted by 3 em than when it was shifted by 1.5 em. These results demonstrated that pigeons can accurately locate an unmarked target area in a two-dimensional vertical arena and that their use of landmarks for spatial localization is similar in severa! respects to that found in open-field spatial search tasks.Many organisms pilot their way back to desired locations by the use of visual landmarks. Some aspects of the spatial relationships between the goal and the surfaces and objects that surround it are encoded and later used to seek the goal. Landmarks are used both to get to the vicinity of the goal over long distances and to pinpoint the goal once the animal is in its vicinity. Gallistel (1990, ch. 5) gives numerous examples of such piloting. The most convincing experimental strategy for demonstrating that an animal uses landmarks in spatial search is to systematically shift landmarks surrounding a goal. If the animal then systematically shifts its searching behavior in space, this indicates that it is relying on the shifted landmarks. Variants of this method have been used to show that landmarks are used by rats (Cheng, 1986;Suzuki, Augerinos, & Black, 1980), gerbils (Collett, Cartwright, & Smith, 1986), hamsters (Etienne, Teroni, Humi, & Portenier, 1990), nutcrackers (Vander Wall, 1982), pigeons (Cheng, This research was supported by NSERC operating grants to the first and second authors. We wish to thank Siew Tan, Stefne Madison, and Lonna Cunningham for assistance with various aspects of this research. Requests for reprints should be addressed to Marcia Spetch, Department of Psychology, University of Alberta, Edmonton, AL Canada TOO 2E9 (e-mail: marcia@ualtamts). 1988Spetch & Edwards, 1988), octopuses (Mather, 1991), ants (Wehner & Raeber, 1979), bees (Cartwright & Cotlett, 1982Dyer & Gould, 1983;von Frisch, 1977), and digger wasps (Tinbergen, 1972).In a series of recent studies on spatial localization...

There was no advantage from the program compared with usual care on the outcomes measured-a finding consistent with recent studies that examined the longer-term effectiveness of other interventions in the first few weeks of back pain symptoms.

Pigeons learned to peck an unmarked 2-cm 2 target area, defined by 4 visually distinct graphic landmarks, on a color monitor with an attached touch frame. The configuration of landmarks and target area was constant during training, but their location on the screen varied across trials. The presence, relative location, and features of the landmarks were manipulated on probe trials. Most birds showed control by only 1 or 2 of the landmarks, and some birds displayed surprisingly accurate search with a single landmark. For individual birds, landmark-removal tests were very consistent with landmark-shift tests in indicating which landmark or landmarks controlled search. However, the dominant landmark varied across birds. Manipulation of landmark color and shape revealed that control was based exclusively on color.