Numerical error monitoring.

Error monitoring has recently been discovered to have informationally rich foundations in the timing domain. Based on the common properties of magnitude-based representations, we hypothesized that judgments on the direction and the magnitude of errors would also reflect their objective counterparts in the numerosity domain. In two experiments, we presented fast sequences of "beeps" with random interstimulus intervals and asked participants to stop the sequence when they thought the target count (7, 11, or 19) had been reached. Participants then judged how close to the target they stopped the sequence, and whether their response undershot or overshot the target. Individual linear regression fits as well as the linear mixed model with a fixed effect of reproduced numerosity on confidence ratings, and participants as independent random effects on the intercept and the slope, revealed significant positive slopes for all the target numerosities. Our results suggest that humans can keep track of the direction and degree of errors in the estimation of discrete quantities, pointing at a numerical-error-monitoring ability.