Doctor of Philosophy
William A. Roberts
Over the past 20 years, the field of animal cognition has seen a dramatic increase in the attention given to the study of cognition in the domestic dog. Since their origin at least 10, 000 years ago, dogs have been artificially selected by humans to protect our homes, guard our livestock, pull our sleds, and a multitude of other functions. Given their close relationship with humans, much of the current research in the area of dog cognition to date has focused on aspects of social cognition. Considerably less attention has been paid to domains that have traditionally been areas of heavy focus in the animal cognition literature. This dissertation focuses on three areas, which are addressed as “fundamental” aspects of cognition—namely, numerical discrimination, interval timing, and spatial memory. These areas were chosen because a.) they are basic processes fundamental to the daily existence of an animal in the wild, and b.) because these topics have been studied rigorously in traditional animal cognition research, yet have received little attention in the area of dog cognition.
In the first set of studies, a numerical discrimination task using sequential presentation of stimuli was used, in which subjects watched as a different number of food items were dropped into each of two bowls. The subjects were then allowed to select and consume the contents of one of the bowls. Although dogs excelled in a 1 vs 0 condition, their performance did not significantly surpass chance across all other ratios. In a second experiment with a single subject, a simultaneous task was used in which stimuli were presented on two magnet boards. Using this simultaneous presentation, ratio effects consistent with both Weber’s Law and the Approximate Number System were demonstrated.
In the second set of studies, interval timing was demonstrated using a fixed interval 30-s schedule, with either a light or a tone + light compound signalling the beginning of each fixed interval. When dogs in the compound group were subsequently tested with 60-s tone-only probe trials, the dogs’ rate of responding peaked near 30 s. When the same dogs were tested with light-only probes, however, no evidence of timing was found, revealing an overshadowing effect of tone over light. In a second experiment, a bi-section task was used in which dogs had to learn to approach one feeder when given an 8-s tone + light signal, and another feeder when given a 2-s tone + light signal. When subsequently tested at intermediate durations, psychophysical curves again showed clear control of timing by the tone stimulus but not by the light stimulus.
The final set of studies were an attempt to investigate both reference and working memory, within a spatial memory task. A win/shift design was used, in which dogs searched for food within the four corners of a large area (an empty classroom in Experiment 1, and an outdoor field in Experiment 2). Food items were hidden under plastic flower pots, which the dogs had previously been trained to knock over. The dogs’ performance in locating rewards hidden consistently in the same location during the test phase (reference memory), was compared to their performance for locating rewards hidden in a different randomly-selected location from trial to trial (working memory). Dogs’ performance varied across subjects, and implications of these individual differences are discussed.
Macpherson, Krista M., "Time, Number, Space, and the Domestic Dog" (2018). Electronic Thesis and Dissertation Repository. 5371.