Do dogs follow Weber’s Law? The role of ratio and difference in quantity preference

Weber’s Law states that the ability to distinguish different stimuli depends on the relative magnitudes of those stimuli. When applied to quantity judgments, this means that the numerical ratio between two quantities (small amount / large amount) will underlie the ability to distinguish the quantities. Ratio-dependent quantification is a hallmark of Weber’s Law that has been demonstrated across a range of species, including dogs. However, other factors such as numerical difference (large amount – small amount) are confounded with ratio but would not support Weber’s Law. Most work on dog quantification abilities has only considered ratio and not difference. Here, we offer dogs a food quantity preference task where we varied both difference and ratio in quantity pairs to investigate which of these factors influences preferences. To address this, dogs could choose to eat one of two plates of food with different quantities of treats on them. We found that, when analyzed separately, both difference and ratio predicted whether the dogs chose the larger quantity of treats. However, when analyzed together, only difference predicted choice when controlling for ratio. In addition, we applied our analysis to data from two previously published studies and corroborated our findings. The results do not support the ratio-dependence required for Weber’s Law, raising questions about its importance for quantity preference tasks in dogs.