Anchoring effects on judgement, estimation, and discrimination of numerosity.

Three experiments (N = 234) examined anchoring effects on judgement, estimation, and discrimination of numerosity. Subjects were anchored by preexposing them to random dot patterns with a mean quantity of 25, 50, or 75 dots. Subsequent testing with patterns having greater or less numerosity than the anchoring point resulted in predictable effects, including positive or negative contrast effects for numerosity judgements (Exp. 1), positive or negative contrast for the numerical estimation of quantity (Exp. 2), and a larger number of errors when subjects attempted simultaneous discrimination between two dot patterns (Exp. 3). The results extend previous findings for anchoring effects to the stimulus dimension of numerosity.