Spatial cognition in three dimensions
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To date, most studies of spatial learning have been conducted in the horizontal plane, with few addressing the vertical dimension. I aimed to investigate learning of 3-D locations by wild, free-living hummingbirds and compare them with rats. In my first experiment, I found that hummingbirds can encode a 3-D rewarded location after a single visit. Using a one-dimensional array, I then found that the birds more readily learned a location in a horizontal than in a vertical linear array. However, the ease of learning was a product not only of the orientation of the array but also of its spacing scale. By the end of training, hummingbirds visited the central rewarded flower and the two adjacent flowers more than they visited the distal flowers for all arrays. However, when the array was horizontal and the flowers spaced 30 cm apart, they learned the absolute location of the rewarded flower. In a diagonal array birds learned the 2-D reward location but they chose at random when tested on a vertically or horizontally oriented array. However, when birds trained in the diagonal array were tested on a 180° rotated diagonal array they chose the flower with the same horizontal component as the rewarded flower rather than with the flower with the same vertical component. Finally in order to compare the spatial learning of animals that move in volumes with those who move in two dimensions I trained hummingbirds and rats to a rewarded location in a cubic maze. Although both hummingbirds and rats learned a 3-D location within a cubic maze, hummingbirds appeared to learn the rewarded location as a 3-D coordinate while rats seemed to learn the vertical and horizontal component of the 3-D location independently. In addition, hummingbirds were more accurate in the vertical and rats in the horizontal, which is consistent with their type of locomotion. More experiments in volumetric, terrestrial and climbing animals are needed in order to determine whether the contrasting search strategies and learning accuracies constitute adaptations to particular spatial niches.
Thesis, PhD Doctor of Philosophy
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