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Pepperberg, I. M., & Brezinsky, M. V. (1991). Acquisition of a relative class concept by an African gray parrot (Psittacus erithacus): discriminations based on relative size. J Comp Psychol, 105(3), 286–294.
Abstract: We report that an African gray parrot (Psittacus erithacus), Alex, responds to stimuli on a relative basis. Previous laboratory studies with artificial stimuli (such as pure tones) suggest that birds make relational responses as a secondary strategy, only after they have acquired information about the absolute values of the stimuli. Alex, however, after learning to respond to a small set of exemplars on the basis of relative size, transferred this behavior to novel situations that did not provide specific information about the absolute values of the stimuli. He responded to vocal questions about which was the larger or smaller exemplar by vocally labeling its color or material, and he responded “none” if the exemplars did not differ in size. His overall accuracy was 78.7%.
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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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Shettleworth, S. J. (1985). Foraging, memory, and constraints on learning. Ann N Y Acad Sci, 443, 216–226.
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Shettleworth, S. J., & Krebs, J. R. (1982). How marsh tits find their hoards: the roles of site preference and spatial memory. J Exp Psychol Anim Behav Process, 8(4), 354–375.
Abstract: Marsh tits (Parus palustris) store single food items in scattered locations and recover them hours or days later. Some properties of the spatial memory involved were analyzed in two laboratory experiments. In the first, marsh tits were offered 97 sites for storing 12 seeds. They recovered a median of 65% of them 2-3 hr later, making only two errors per seed while doing so. Over trials, they used some sites more often than others, but during recovery they were more likely to visit a site of any preference value if they had stored a seed there that day than if they had not. Recovery performance was much worse if the experimenters moved the seeds between storage and recovery. A fixed search strategy that had some of the same average properties as the tits' search behavior also did worse than the real birds. In Experiment 2, any tendency to visit the same sites on successive daily tests in the aviary was placed in opposition to memory for storage sites by allowing the tits to store more seeds 2 hr after storing a first batch. They tended to avoid individual storage sites holding seeds from the first batch. When the tits searched for all the seeds 2 hr later, they tended to recover more seeds from the second batch than from the first, i.e., there was a recency effect.
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Zentall, T. R., Roper, K. L., & Sherburne, L. M. (1995). Most directed forgetting in pigeons can be attributed to the absence of reinforcement on forget trials during training or to other procedural artifacts. J Exp Anal Behav, 63(2), 127–137.
Abstract: In research on directed forgetting in pigeons using delayed matching procedures, remember cues, presented in the delay interval between sample and comparisons, have been followed by comparisons (i.e., a memory test), whereas forget cues have been followed by one of a number of different sample-independent events. The source of directed forgetting in delayed matching to sample in pigeons was examined in a 2 x 2 design by independently manipulating whether or not forget-cue trials in training ended with reinforcement and whether or not forget-cue trials in training included a simultaneous discrimination (involving stimuli other than those used in the matching task). Results were consistent with the hypothesis that reinforced responding following forget cues is sufficient to eliminate performance deficits on forget-cue probe trials. Only when reinforcement was omitted on forget-cue trials in training (whether a discrimination was required or not) was there a decrement in accuracy on forget-cue probe trials. When reinforcement is present, however, the pattern of responding established during and following a forget cue in training may also play a role in the directed forgetting effect. These findings support the view that much of the evidence for directed forgetting using matching procedures may result from motivational and behavioral artifacts rather than the loss of memory.
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Hampton, R. R., Sherry, D. F., Shettleworth, S. J., Khurgel, M., & Ivy, G. (1995). Hippocampal volume and food-storing behavior are related in parids. Brain Behav Evol, 45(1), 54–61.
Abstract: The size of the hippocampus has been previously shown to reflect species differences and sex differences in reliance on spatial memory to locate ecologically important resources, such as food and mates. Black-capped chickadees (Parus atricapillus) cached more food than did either Mexican chickadees (P. sclateri) or bridled titmice (P. wollweberi) in two tests of food storing, one conducted in an aviary and another in smaller home cages. Black-capped chickadees were also found to have a larger hippocampus, relative to the size of the telencephalon, than the other two species. Differences in the frequency of food storing behavior among the three species have probably produced differences in the use of hippocampus-dependent memory and spatial information processing to recover stored food, resulting in graded selection for size of the hippocampus.
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Whiten, A., Custance, D. M., Gomez, J. C., Teixidor, P., & Bard, K. A. (1996). Imitative learning of artificial fruit processing in children (Homo sapiens) and chimpanzees (Pan troglodytes). J Comp Psychol, 110(1), 3–14.
Abstract: Observational learning in chimpanzees and young children was investigated using an artificial fruit designed as an analog of natural foraging problems faced by primates. Each of 3 principal components could be removed in 2 alternative ways, demonstration of only one of which was watched by each subject. This permitted subsequent imitation by subjects to be distinguished from stimulus enhancement. Children aged 2-4 years evidenced imitation for 2 components, but also achieved demonstrated outcomes through their own techniques. Chimpanzees relied even more on their own techniques, but they did imitate elements of 1 component of the task. To our knowledge, this is the first experimental evidence of chimpanzee imitation in a functional task designed to simulate foraging behavior hypothesized to be transmitted culturally in the wild.
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Hampton, R. R., & Shettleworth, S. J. (1996). Hippocampal lesions impair memory for location but not color in passerine birds. Behav Neurosci, 110(4), 831–835.
Abstract: The effects of hippocampal complex lesions on memory for location and color were assessed in black-capped chickadees (Parus atricapillus) and dark-eyed juncos (Junco hyemalis) in operant tests of matching to sample. Before surgery, most birds were more accurate on tests of memory for location than on tests of memory for color. Damage to the hippocampal complex caused a decline in memory for location, whereas memory for color was not affected in the same birds. This dissociation indicates that the avian hippocampus plays an important role in spatial cognition and suggests that this brain structure may play no role in working memory generally.
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Hampton, R. R., & Shettleworth, S. J. (1996). Hippocampus and memory in a food-storing and in a nonstoring bird species. Behav Neurosci, 110(5), 946–964.
Abstract: Food-storing birds maintain in memory a large and constantly changing catalog of the locations of stored food. The hippocampus of food-storing black-capped chickadees (Parus atricapillus) is proportionally larger than that of nonstoring dark-eyed juncos (Junco hyemalis). Chickadees perform better than do juncos in an operant test of spatial non-matching-to-sample (SNMTS), and chickadees are more resistant to interference in this paradigm. Hippocampal lesions attenuate performance in SNMTS and increase interference. In tests of continuous spatial alternation (CSA), juncos perform better than chickadees. CSA performance also declines following hippocampal lesions. By itself, sensitivity of a given task to hippocampal damage does not predict the direction of memory differences between storing and nonstoring species.
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Brodbeck, D. R. (1997). Picture fragment completion: priming in the pigeon. J Exp Psychol Anim Behav Process, 23(4), 461–468.
Abstract: It has been suggested that the system behind implicit memory in humans is evolutionarily old and that animals should readily show priming. In Experiment 1, a picture fragment completion test was used to test priming in pigeons. After pecking a warning stimulus, pigeons were shown 2 partially obscured pictures from different categories and were always reinforced for choosing a picture from one of the categories. On control trials, the warning stimulus was a picture of some object (not from the S+ or S- category), on study trials the warning stimulus was a picture to be categorized on the next trial, and on test trials the warning stimulus was a randomly chosen picture and the S+ picture was the warning stimulus seen on the previous trial. Categorization was better on study and test trials than on control trials. Experiment 2 ruled out the possibility that the priming effect was caused by the pigeons' responding to familiarity by using warning stimuli from both S+ and S- categories. Experiment 3 investigated the time course of the priming effect.
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