Perceived numerosity, item arrangement, and expectancy

Ten sets of dots ranging in number from 7 to 91 per set were presented to 54 subjects. Half were arranged regularly and half randomly. The regular sets were overestimated by an average of 22%, while the random were underestimated by 16% compared with the physical number. Evidence was presented showing that subjects expect results in the opposite direction. The findings are discussed in relation to the expectancy-contrast model of Birnbaum and Veit.