Numerical Perception Biased by Saliency

How do people process numerosity? Do they rely on general magnitude processing (e.g. area, density, etc.)1,2,3? Alternatively, do they depend on a designated module underlying numerosity judgements4,5? In a 2016 paper, Cicchini and colleagues6 show results that strongly support the latter. They demonstrated that humans automatically perceive and spontaneously use numerosity rather than other physical magnitudes (i.e. area of convex hull or density) when asked to make comparison judgments. Here we present an alternative account for their findings. We suggest that saliency of the different attributes of the stimuli (i.e. numerosity, area of convex hull and density) can bias participant’s strategy. We show that in Cicchini et al.’s design, indeed numerosity was more salient than the other stimuli dimensions. We demonstrate that when saliency of another property is increased, participants tend to rely on it instead of numerosity. Taken together, this challenges Cicchini et al.’s conclusion that numerosity is processed automatically.