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Boysen, S. T., & Berntson, G. G. (1995). Responses to quantity: perceptual versus cognitive mechanisms in chimpanzees (Pan troglodytes). J Exp Psychol Anim Behav Process, 21(1), 82–86.
Abstract: Two chimpanzees were trained to select among 2 different amounts of candy (1-6 items). The task was designed so that selection of either array by the active (selector) chimpanzee resulted in that array being given to the passive (observer) animal, with the remaining (nonselected) array going to the selector. Neither animal was able to select consistently the smaller array, which would reap the larger reward. Rather, both animals preferentially selected the larger array, thereby receiving the smaller number of reinforcers. When Arabic numerals were substituted for the food arrays, however, the selector animal evidenced more optimal performance, immediately selecting the smaller numeral and thus receiving the larger reward. These findings suggest that a basic predisposition to respond to the perceptual-motivational features of incentive stimuli can interfere with task performance and that this interference can be overridden when abstract symbols serve as choice stimuli.
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Boysen, S. T., Bernston, G. G., Hannan, M. B., & Cacioppo, J. T. (1996). Quantity-based interference and symbolic representations in chimpanzees (Pan troglodytes). J Exp Psychol Anim Behav Process, 22(1), 76–86.
Abstract: Five chimpanzees with training in counting and numerical skills selected between 2 arrays of different amounts of candy or 2 Arabic numerals. A reversed reinforcement contingency was in effect, in which the selected array was removed and the subject received the nonselected candies (or the number of candies represented by the nonselected Arabic numeral). Animals were unable to maximize reward by selecting the smaller array when candies were used as array elements. When Arabic numerals were substituted for the candy arrays, all animals showed an immediate shift to a more optimal response strategy of selecting the smaller numeral, thereby receiving the larger reward. Results suggest that a response disposition to the high-incentive candy stimuli introduced a powerful interference effect on performance, which was effectively overridden by the use of symbolic representations.
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Burke, D., Cieplucha, C., Cass, J., Russell, F., & Fry, G. (2002). Win-shift and win-stay learning in the short-beaked echidna (Tachyglossus aculeatus). Anim. Cogn., 5(2), 79–84.
Abstract: Numerous previous investigators have explained species differences in spatial memory performance in terms of differences in foraging ecology. In three experiments we attempted to extend these findings by examining the extent to which the spatial memory performance of echidnas (or “spiny anteaters”) can be understood in terms of the spatio-temporal distribution of their prey (ants and termites). This is a species and a foraging situation that have not been examined in this way before. Echidnas were better able to learn to avoid a previously rewarding location (to “win-shift”) than to learn to return to a previously rewarding location (to “win-stay”), at short retention intervals, but were unable to learn either of these strategies at retention intervals of 90 min. The short retention interval results support the ecological hypothesis, but the long retention interval results do not.
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Byrne, T., Sutphin, G., & Poling, A. (1998). Acquisition, extinction, and reacquisition of responding with delayed and immediate reinforcement. Behav. Process., 43(1), 97–101.
Abstract: The present study investigated acquisition, extinction, and reacquisition of free-operant responding when rats' lever presses produced water after a resetting delay of 0, 10, 20, or 30 s. Results indicated that: (1) responding was acquired rapidly at all delays without shaping or autoshaping; (2) resistance to extinction was directly related to delay length and inversely related to intermittency of reinforcement; (3) responding acquired with delayed reinforcement recovered less rapidly from extinction, and was less efficient, than responding acquired with immediate reinforcement. Comparing these results with those of studies using discrete-trials and free-operant procedures with no reinforcement delay suggest that the specific conditions under which behavior is maintained determines, in part, the behavioral effects of delay and intermittency of reinforcement.
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Cerutti, D. T., & Staddon, J. E. R. (2004). Immediacy versus anticipated delay in the time-left experiment: a test of the cognitive hypothesis. J Exp Psychol Anim Behav Process, 30(1), 45–57.
Abstract: In the time-left experiment (J. Gibbon & R. M. Church, 1981), animals are said to compare an expectation of a fixed delay to food, for one choice, with a decreasing delay expectation for the other, mentally representing both upcoming time to food and the difference between current time and upcoming time (the cognitive hypothesis). The results of 2 experiments support a simpler view: that animals choose according to the immediacies of reinforcement for each response at a time signaled by available time markers (the temporal control hypothesis). It is not necessary to assume that animals can either represent or subtract representations of times to food to explain the results of the time-left experiment.
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Christensen, J. W. (2012). Object habituation in horses: Voluntary vs. negatively reinforced approach to frightening stimuli. In K. Krueger (Ed.), Proceedings of the 2. International Equine Science Meeting (Vol. in press). Wald: Xenophon Publishing.
Abstract: The ability and ease of horses to habituate to frightening stimuli greatly increases safety in the horse-human relationship. Several different techniques have been suggested for habituation training of horses and under certain conditions, preventing animals from avoidance reactions during exposure to frightening stimuli is believed to facilitate habituation. Response prevention does, however, lead to a loss of control, which is a known stress inducer in both animals and humans. This experiment investigated whether horses show increased stress responses when negatively reinforced to approach a mildly frightening stimulus, compared to horses allowed to voluntarily explore the same stimulus. We further investigated whether the prevention of avoidance responses in horses that are negatively reinforced to approach the stimulus, facilitates habituation to the stimulus. Twenty-two 2-3 years old Danish warmblood geldings were included in the study. Half of the horses (NR group) were negatively reinforced (through halter and rope pressure) by a familiar human handler to approach a collection of frightening objects (six open and colourful umbrellas) placed in a semi-circle in a familiar test arena. The other half of the horses were released in the arena and were free to avoid or explore the objects (VOL group). On the next day, all horses were exposed to the objects again without a human to investigate the rate of habituation. Behavioural and heart rate responses were recorded on both days. Data were analysed in a two way repeated measures ANOVA and post hoc analysed via the Holm-Sidak method. In the VOL group, all horses initially chose to avoid the unknown objects, whereas the handler managed to get all horses in the NR group to approach and stand next to the objects within the first 2-min session. As expected, horses in the NR group had a significantly longer duration of alertness (sec, mean ± se: NR: 23 ± 4.1 vs. VOL: 16 ± 4.7, P=0.026) and a higher max HR in the first session (bpm, mean ± se: NR: 106 ± 5.2 vs. VOL: 88 ± 4.4, P=0.004). On the next day, however, the NR horses spent significantly less time investigating the objects (sec, mean ± se: NR: 13 ± 4.1 vs. VOL: 24 ± 6.0, P=0.005) and had a shorter latency to approach a feed container, placed next to the objects (sec, mean ± se: NR: 25 ± 3.9 vs. VOL: 47 ± 16.2, P=0.031), indicating increased habituation. In conclusion, negatively reinforced approach to mildly frightening objects appears to increase stress responses during the initial exposure, but also to facilitate habituation in young horses.
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Christensen, J. W., Ahrendt, L. P., Lintrup, R., Gaillard, C., Palme, R., & Malmkvist, J. (2012). Does learning performance in horses relate to fearfulness, baseline stress hormone, and social rank? In Applied Animal Behaviour Science (Vol. 140, pp. 44–52).
Abstract: The ability of horses to learn and remember new tasks is fundamentally important for their use by humans. Fearfulness may, however, interfere with learning, because stimuli in the environment can overshadow signals from the rider or handler. In addition, prolonged high levels of stress hormones can affect neurons within the hippocampus; a brain region central to learning and memory. In a series of experiments, we aimed to investigate the link between performance in two learning tests, the baseline level of stress hormones, measured as faecal cortisol metabolites (FCM), fearfulness, and social rank. Twenty-five geldings (2 or 3 years old) pastured in one group were included in the study. The learning tests were performed by professional trainers and included a number of predefined stages during which the horses were gradually trained to perform exercises, using either negative (NR) or positive reinforcement (PR). Each of the learning tests lasted 3 days; 7min/horse/day. The NR test was repeated in a novel environment. Performance, measured as final stage in the training programme, and heart rate (HR) were recorded. Faeces were collected on four separate days where the horses had been undisturbed at pasture for 48h. Social rank was determined through observations of social interactions during feeding. The fear test was a novel object test during which behaviour and HR were recorded. Performance in the NR and PR learning tests did not correlate. In the NR test, there was a significant, negative correlation between performance and HR in the novel environment (rS=-0.66, P<0.001, i.e. nervous horses had reduced performance), whereas there was no such correlation in the home environment (both NR and PR). Behavioural reactions in the fear test correlated significantly with performance in the NR test in the novel environment (e.g. object alertness and final stage: rS=-0.43, P=0.04), suggesting that performance under unfamiliar, stressful conditions may be predicted by behavioural responses in a fear test. There was a negative correlation between social rank and baseline stress hormones (rS=-0.43, P=0.04), i.e. high rank corresponded to low FCM concentrations, whereas neither rank nor FCM correlated with fearfulness or learning performance. We conclude that performance under stressful conditions is affected by activation of the sympathetic nervous system during training and related to behavioural responses in a standardised fear test. Learning performance in the home environment, however, appears unrelated to fearfulness, social rank and baseline FCM levels.
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Christensen, J. W., Rundgren, M., & Olsson, K. (2006). Training methods for horses: habituation to a frightening stimulus. Equine Vet J, 38(5), 439–443.
Abstract: REASONS FOR PERFORMING STUDY: Responses of horses in frightening situations are important for both equine and human safety. Considerable scientific interest has been shown in development of reactivity tests, but little effort has been dedicated to the development of appropriate training methods for reducing fearfulness. OBJECTIVES: To investigate which of 3 different training methods (habituation, desensitisation and counter-conditioning) was most effective in teaching horses to react calmly in a potentially frightening situation. HYPOTHESES: 1) Horses are able to generalise about the test stimulus such that, once familiar with the test stimulus in one situation, it appears less frightening and elicits a reduced response even when the stimulus intensity is increased or the stimulus is presented differently; and 2) alternative methods such as desensitisation and counter-conditioning would be more efficient than a classic habituation approach. METHODS: Twenty-seven naive 2-year-old Danish Warmblood stallions were trained according to 3 different methods, based on classical learning theory: 1) horses (n = 9) were exposed to the full stimulus (a moving, white nylon bag, 1.2 x 0.75 m) in 5 daily training sessions until they met a predefined habituation criterion (habituation); 2) horses (n = 9) were introduced gradually to the stimulus and habituated to each step before the full stimulus was applied (desensitisation); 3) horses (n = 9) were trained to associate the stimulus with a positive reward before being exposed to the full stimulus (counter-conditioning). Each horse received 5 training sessions of 3 min per day. Heart rate and behavioural responses were recorded. RESULTS: Horses trained with the desensitisation method showed fewer flight responses in total and needed fewer training sessions to learn to react calmly to test stimuli. Variations in heart rate persisted even when behavioural responses had ceased. In addition, all horses on the desensitisation method eventually habituated to the test stimulus whereas some horses on the other methods did not. CONCLUSIONS AND POTENTIAL RELEVANCE: Desensitisation appeared to be the most effective training method for horses in frightening situations. Further research is needed in order to investigate the role of positive reinforcement, such as offering food, in the training of horses.
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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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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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