Animal cognition
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Humans and nonhuman primates can learn about the organization of stimuli in the environment using implicit sequential pattern learning capabilities. However, most previous artificial grammar learning studies with nonhuman primates have involved relatively simple grammars and short input sequences. The goal in the current experiments was to assess the learning capabilities of monkeys on an artificial grammar-learning task that was more complex than most others previously used with nonhumans. ⋯ In a subsequent generalization phase, subjects generalized their knowledge to novel sequences, responding significantly faster to novel instances of sequences produced using the familiar grammar compared to those constructed using an unfamiliar grammar. These results reveal that rhesus monkeys can learn and generalize the statistical structure inherent in an artificial grammar that is as complex as some used with humans, for sequences up to eight items long. These findings are discussed in relation to whether or not rhesus macaques and other primate species possess implicit sequence learning abilities that are similar to those that humans draw upon to learn natural language grammar.
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We examined attentional biases for social and non-social emotional stimuli in young adult men and compared the results to those of male rhesus monkeys (Macaca mulatta) previously tested in a similar dot-probe task (King et al. in Psychoneuroendocrinology 37(3):396-409, 2012). Recognition memory for these stimuli was also analyzed in each species, using a recognition memory task in humans and a delayed non-matching-to-sample task in monkeys. We found that both humans and monkeys displayed a similar pattern of attentional biases toward threatening facial expressions of conspecifics. ⋯ Yet, selective attention to threat was weaker in humans than in monkeys, suggesting that regulatory mechanisms enable non-anxious humans to reduce sensitivity to social threat in this paradigm, likely through enhanced prefrontal control and reduced amygdala activation. In addition, the findings emphasize important differences in attentional biases to social versus non-social threat in both species. Differences in the impact of emotional stimuli on recognition memory between monkeys and humans will require further study, as methodological differences in the recognition tasks may have affected the results.
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Domestic cats have had a 10,000-year history of cohabitation with humans and seem to have the ability to communicate with humans. However, this has not been widely examined. We studied 20 domestic cats to investigate whether they could recognize their owners by using voices that called out the subjects' names, with a habituation-dishabituation method. ⋯ Of the 20 cats, 15 demonstrated a lower response magnitude to the third voice than to the first voice. These habituated cats showed a significant rebound in response to the subsequent presentation of their owners' voices. This result indicates that cats are able to use vocal cues alone to distinguish between humans.
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Recent studies have revealed that dogs often perform well in cognitive tasks in the social domain, but rather poorly in the physical domain. This dichotomy has led to the hypothesis that the domestication process might have enhanced the social cognitive skills of dogs (Hare et al. in Science 298:1634-1636, 2002; Miklósi et al. in Curr Biol 13:763-766, 2003) but at the same time had a detrimental effect on their physical cognition (Frank in Z Tierpsychol 5:389-399, 1980). Despite the recent interest in dog cognition and especially the effects of domestication, the latter hypothesis has hardly been tested and we lack detailed knowledge of the physical understanding of wolves in comparison with dogs. ⋯ We found that at the group level, dogs were more prone to commit the proximity error, while the wolves showed a stronger side bias. Neither wolves nor dogs showed an instantaneous understanding of means-end connection, but made different mistakes. Thus, the performance of the wolves and dogs in this string-pulling task did not confirm that domestication has affected the physical cognition of dogs.
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Comparative Study
Decision making at a crossroad: why to go straight ahead, retrace a path, or turn sideways?
In order to uncover processes in the acquisition of spatial representation, we tested voles, jirds, and mice in a dark grid maze-a relatively homogenous environment comprising 16 identical equispaced crossroads and similar choice of paths at each crossroad. The three species initially displayed a tendency to retrace sections of their recently traversed path, perhaps indicating exploration and learning of an unfamiliar environment by virtue of repetition. All three species displayed the same decision making at crossroads. ⋯ The incidence of turning sideways, in being more difficult than forward progression and retracing, yet necessary in a restricted maze space, did not change over repeated visits to crossroads. Altogether, decision making at a crossroad may be described as going straight ahead for simplicity, retracing a path to memorize it, or turning sideways at a constant rate. The present tests in the grid maze illustrate how tangible entities (crossroads, paths) are integrated during the early phase of acquiring an abstract representation (map) of the maze.