Reinforcer effectiveness in dogs—The influence of quantity and quality

Reinforcer effectiveness refers to the reinforcer’s ability to control the subject’s target behaviour and is therefore critical to training success. Yet animals’ preferences, and the effectiveness of different rewards to function as reinforcers, are often assumed without scientific investigation. Here we explored the influence of reward quality, quantity and changes in reward value on motivation in domestic dogs. Subjects were trained to traverse a runway for a food reward. In Study 1, the quantity of food was varied (1 vs 5 pieces of dry food), while in Study 2, food quality was varied (1 piece of sausage vs 1 piece of dry food). Dogs were tested in two conditions (counterbalanced). In the unshifted condition, they received the low value reward in all of ten trials; in the shifted condition, reward value was altered (high value: trials 1–4 and 9–10; low value: trials 5–8). While preliminary preference tests had confirmed the relative value of the presumed high and low value rewards for both quantity and quality, dogs' responses in the runway task differed between the quality and quantity studies. Dogs ran significantly faster for the higher quality food compared to the lower quality food, confirming greater reinforcer effectiveness of the preferred food type. In contrast, there was no significant effect of food quantity on running speed at any stage. Higher quality rewards therefore appear to entail greater incentive motivation in dogs than a greater quantity of a lower value reward, with reward-specific habituation needing to be considered.