Training numerousness to numerosity in the dog (Canis lupus familiaris)

Dogs show numerousness, which is the ability to identify the larger of two stimuli, most often the number of treats on a plate. However, dogs seem to use mechanisms other than counting to make this discrimination. This study builds on existing research by controlling for (a) olfaction, (b) the surface area of the stimuli, and (c) delivery of a single reinforcer contingent on correct choices in the trained task. Nine dogs were trained to select a dish with 5 dots/treats in a sealed container when presented with comparison stimuli of 1, 4, and 9 dots/treats. The dogs showed numerousness in discriminating between dishes with 1 versus 5 dots, with consistent performance of more than 80% correct. Two dogs could discriminate 4 versus 5 dots, and three dogs learned the 9- versus 5-dot discrimination in which there is a conflict between selecting the larger option and selecting the 5 dots to gain reinforcement in the task. Knowledge of numerical competency, particularly training dogs to select the nonreinforced choice, can offer strategies to facilitate cognitive enrichment and learning in animals or offer enhancement of the capabilities of working dogs where the concept of number might be advantageous in providing additional skills.