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Fairhurst, S., Gallistel, C. R., & Gibbon, J. (2003). Temporal landmarks: proximity prevails. Anim. Cogn., 6(2), 113–120.
Abstract: Subjects in conditioning experiments time their conditioned responses relative to the onsets of the conditioned stimuli (CSs). These onsets are temporal landmarks, by reference to which subjects may estimate the location of the unconditioned stimulus (US) in time. In a serial compound conditioning paradigm, a long duration CS comes on first, followed later by a second shorter CS, creating both a long-range and a short-range predictor of the US. We ask whether displacing the short-range predictor relative to the long-range predictor causes subjects to strike a compromise between the different temporal locations predicted by the two CSs. In three experiments with pigeons, we varied the training conditions so as to favor or militate against this outcome. However, in all conditions, there was no compromise; after the onset of the displaced short-range CS, the timing of conditioned responding was governed by it alone. This result contrasts with the compromises that are seen when the feeding time predicted by a CS is put in conflict with the time predicted by the circadian clock, and with the similar compromises sometimes seen when a nearby spatial landmark is displaced relative to a larger spatial context.
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Zentall, T. R., & Clement, T. S. (2002). Memory mechanisms in pigeons: evidence of base-rate neglect. J Exp Psychol Anim Behav Process, 28(1), 111–115.
Abstract: In delayed matching to sample, once acquired, pigeons presumably choose comparisons according to their memory for (the strength of) the sample. When memory for the sample is sufficiently weak, comparison choice should depend on the history of reinforcement associated with each of the comparison stimuli. In the present research, pigeons acquired two matching tasks in which Sample S1 was associated with one comparison from each task, C1 and C3, whereas Sample S2 was associated with Comparison C2, and Sample S3 was associated with Comparison C4. As the retention interval increased, the pigeons showed a bias to choose the comparison (C1 or C3) associated with the more frequently occurring sample (S1). Thus, pigeons were sensitive also to the (irrelevant) likelihood that each of the samples was presented. The results suggest that pigeons may allow their reference memory for the overall sample frequency to influence comparison choice, independent of the comparison stimuli present.
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Goto, K., Wills, A. J., & Lea, S. E. G. (2004). Global-feature classification can be acquired more rapidly than local-feature classification in both humans and pigeons. Anim. Cogn., 7(2), 109–113.
Abstract: When humans process visual stimuli, global information often takes precedence over local information. In contrast, some recent studies have pointed to a local precedence effect in both pigeons and nonhuman primates. In the experiment reported here, we compared the speed of acquisition of two different categorizations of the same four geometric figures. One categorization was on the basis of a local feature, the other on the basis of a readily apparent global feature. For both humans and pigeons, the global-feature categorization was acquired more rapidly. This result reinforces the conclusion that local information does not always take precedence over global information in nonhuman animals.
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Clement, T. S., Feltus, J. R., Kaiser, D. H., & Zentall, T. R. (2000). “Work ethic” in pigeons: reward value is directly related to the effort or time required to obtain the reward. Psychon Bull Rev, 7(1), 100–106.
Abstract: Stimuli associated with less effort or with shorter delays to reinforcement are generally preferred over those associated with greater effort or longer delays to reinforcement. However, the opposite appears to be true of stimuli that follow greater effort or longer delays. In training, a simple simultaneous discrimination followed a single peck to an initial stimulus (S+FR1 S-FR1) and a different simple simultaneous discrimination followed 20 pecks to the initial stimulus (S+FR20 S-FR20). On test trials, pigeons preferred S+FR20 over S+FR1 and S-FR20 over S-FR1. These data support the view that the state of the animal immediately prior to presentation of the discrimination affects the value of the reinforcement that follows it. This contrast effect is analogous to effects that when they occur in humans have been attributed to more complex cognitive and social factors.
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Katz, J. S., & Wright, A. A. (2006). Same/different abstract-concept learning by pigeons. J Exp Psychol Anim Behav Process, 32(1), 80–86.
Abstract: Eight pigeons were trained and tested in a simultaneous same/different task. After pecking an upper picture, they pecked a lower picture to indicate same or a white rectangle to indicate different. Increases in the training set size from 8 to 1,024 items produced improved transfer from 51.3% to 84.6%. This is the first evidence that pigeons can perform a two-item same/different task as accurately with novel items as training items and both above 80% correct. Fixed-set control groups ruled out training time or transfer testing as producing the high level of abstract-concept learning. Comparisons with similar experiments with rhesus and capuchin monkeys showed that the ability to learn the same/different abstract concept was similar but that pigeons require more training exemplars.
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Urcuioli, P. J., & Zentall, T. R. (1986). Retrospective coding in pigeons' delayed matching-to-sample. J Exp Psychol Anim Behav Process, 12(1), 69–77.
Abstract: In this study we examined how coding processes in pigeons' delayed matching-to-sample were affected by the stimuli to be remembered. In Experiment 1, two groups of pigeons initially learned 0-delay matching-to-sample with identical comparison stimuli (vertical and horizontal lines) but with different sample stimuli (red and green hues or vertical and horizontal lines). Longer delays were then introduced between sample offset and comparison onset to assess whether pigeons were prospectively coding the same events (viz., the correct line comparisons) or retrospectively coding different events (viz., their respective sample stimuli). The hue-sample group matched more accurately and showed a slower rate of forgetting than the line-sample group. In Experiment 2, pigeons were trained with either hues or lines as both sample and comparison stimuli, or with hue samples and line comparisons or vice versa. Subsequent delay tests revealed that the hue-sample groups remembered more accurately and generally showed slower rates of forgetting than the line-sample groups. Comparison dimension had little or no effect on performance. Together, these data suggest that pigeons retrospectively code the samples in delayed matching-to-sample.
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Zentall, T. R., Sherburne, L. M., Roper, K. L., & Kraemer, P. J. (1996). Value transfer in a simultaneous discrimination appears to result from within-event pavlovian conditioning. J Exp Psychol Anim Behav Process, 22(1), 68–75.
Abstract: When pigeons acquire a simple simultaneous discrimination, some of the value acquired by the S+ transfers to the S-. The mechanism underlying this transfer of value was examined in three experiments. In Experiment 1, pigeons trained on two simultaneous discriminations (A + B- and C +/- D-) showed a preference for B over D. This preference was reduced, however, following the devaluation of A. In Experiment 2, when after the same original training, value was given to D, the pigeons' preference for C did not significantly increase. In Experiment 3, when both discriminations involved partial reinforcement (S +/-), A + C- training resulted in a preference for B over D, whereas B + D- training resulted in a preference for A over C. Thus, simultaneous discrimination training appears to result in bidirectional within-event conditioning involving the S+ and S-.
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Clement, T. S., & Zentall, T. R. (2002). Second-order contrast based on the expectation of effort and reinforcement. J Exp Psychol Anim Behav Process, 28(1), 64–74.
Abstract: Pigeons prefer signals for reinforcement that require greater effort (or time) to obtain over those that require less effort to obtain (T. S. Clement, J. Feltus, D. H. Kaiser, & T. R. Zentall, 2000). Preference was attributed to contrast (or to the relatively greater improvement in conditions) produced by the appearance of the signal when it was preceded by greater effort. In Experiment 1, the authors of the present study demonstrated that the expectation of greater effort was sufficient to produce such a preference (a second-order contrast effect). In Experiments 2 and 3, low versus high probability of reinforcement was substituted for high versus low effort, respectively, with similar results. In Experiment 3, the authors found that the stimulus preference could be attributed to positive contrast (when the discriminative stimuli represented an improvement in the probability of reinforcement) and perhaps also negative contrast (when the discriminative stimuli represented reduction in the probability of reinforcement).
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Wagner, G. (1975). [Flight leadership in flocks of homing pigeons]. Z. Tierpsychol., (39), 61–74.
Abstract: Groups of 3-5 homing pigeons individually recognizable by different colours of their plumage were followed by helicopter on their way home. In most cases the animals flew together as a group with frequently changing leadership. Flight formations in terms of leadership were noted every minute. It was examined statistically whether the flight order varies at random or whether there are leading and led birds. In 6 out of 7 experiments with groups of 4-5 pigeons flight order was far from random, one or two pigeons proving to be leaders. In only one experiment leadership did not differ from a random distribution. No correlation could be found between the tendency to lead within a group and homing performance of the single pigeon when released individually.
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Urcuioli, P. J., DeMarse, T. B., & Zentall, T. R. (1998). Transfer across delayed discriminations: II. Differences in the substitutability of initial versus test stimuli. J Exp Psychol Anim Behav Process, 24(1), 47–59.
Abstract: In 2 experiments, pigeons were trained on, and then transferred to, delayed simple discriminations in which the initial stimuli signalled reinforcement versus extinction following a retention interval. Experiment 1 showed that discriminative responding on the retention test transferred to novel test stimuli that had appeared in another delayed simple discrimination but not to stimuli having the same reinforcement history off-baseline. By contrast, Experiment 2 showed that performances transferred to novel initial stimuli whether they had been trained on-baseline or off-baseline. These results suggest that the test stimuli in delayed simple discriminations acquire control over responding only in the memory task itself. On the other hand, control by the initial stimuli, if coded as outcome expectancies, does not require such task-specific training.
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