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Two experiments examined pigeons' generalization to intermediate forms following training of concept discriminations. In Experiment 1, the training stimuli were sets of images of dogs and cats, and the transfer stimuli were head/body chimeras, which humans tend to categorize more readily in terms of the head part rather than the body part. In Experiment 2, the training stimuli were sets of images of heads of dogs and cats, and the intermediate stimuli were computer-generated morphs. In both experiments, pigeons learned the concept discrimination quickly and generalized with some decrement to novel instances of the categories. In both experiments, transfer tests were carried out with intermediate forms generated from both familiar and novel exemplars of the training sets. In Experiment 1, the pigeons' transfer performance, unlike that of human infants exposed to similar stimuli, was best predicted by the body part of the stimulus when the chimeras were formed from familiar exemplars. Spatial frequency analysis of the stimuli showed that the body parts were richer in high spatial frequencies than the head parts, so these data are consistent with the hypothesis that categorization is more dependent on local stimulus features in pigeons than in humans. There was no corresponding trend when the chimeras were formed from novel exemplars. In Experiment 2, when morphs of training stimuli were used, response rates declined smoothly as the proportion of the morph contributed by the positive stimulus fell, although results with morphs of novel stimuli were again less orderly. [ABSTRACT FROM AUTHOR]

We conducted four experiments with 56 adult dogs (Canis lupus familiaris) involving tasks where food was dropped through an opaque tube connected either vertically or diagonally to one of two or three goal boxes. In the first experiment, modelled after studies with children and primates, the dogs first searched significantly more often in the location directly beneath the drop-off point (a gravity bias), although this box was not connected with the tube. These results are comparable to those of human infants and cotton-top tamarins. Experiments 2–4 tested which problem solving strategy the dogs applied to find the food. Results show that they do not understand the physical mechanism of the tube itself, and they apply one of three search strategies: search the gravity box (the one below the drop-off box); search the box in the middle; learn the correct location of the goal box. When the goal box was in the same location the dogs learned to search there over trials, that is, they learned to ‘defy gravity’, but when the location of the goal box changed over trials they showed no learning. These findings are compared with those from human infants and cotton-top tamarins: like these species, the dogs can learn to overcome a gravity bias, but only when the reward is to be found in a consistent location. [ABSTRACT FROM AUTHOR]