Is the approximate number system capacity limited? Extended display duration does not increase the limits of linear number estimation.

The approximate number system (ANS) is widely regarded as handling numbers beyond the subitizing range. However, a review of a variety of historical data suggests there is a sharp break in the estimation of visuospatial number at about 20 items. Estimates below 20 tend to be unbiased. Those above 20 tend to show underestimation that can be well-fit by a power function with an exponent less than one. Here we manipulate display duration between subjects to confirm that this break is not simply an artifact of brief displays, but seems to reflect a shift in perceptual magnitude estimation from an ANS (unbiased estimation) to a correlated numerosity system (with log scaling). Detailed analysis of both response time and variability suggests that the sharp break at 20 observed here may reflect a capacity limitation in a linear accumulator system, which gives way to alternative magnitude information beyond 20. Implications for studies of number comparison and math performance are discussed. (PsycInfo Database Record (c) 2023 APA, all rights reserved).