Comparative Judgment of Familiar Objects Is Modulated by Their Size

Perceptual decisions such as that we have more strawberries than apples left in our fruit basket seem to be made effortlessly. However, it is not examined yet whether such decisions are also biased by the size of the objects, just like numerosity comparisons with meaningless dot arrays. We presented two homogeneous sets of larger and smaller fruits (e.g., three apples and four strawberries), and participants had to indicate which set was more numerous. Although accuracy was nearly perfect, a strong congruency effect was found in reaction times, showing it is more difficult to compare the numerosities of sets of 2 apples and 3 strawberries than the opposite, that is, 3 apples and 2 strawberries. Because the stimuli were selected to simulate everyday conditions as much as possible, the present results suggest that most likely also comparative numerosity judgment in daily life is biased by nonnumerical cues such as size of the objects.