Numerosity Discrimination

Your approximate number system (ANS) lets you quickly estimate quantities without counting. Its precision is described by the Weber fraction. If your Weber fraction is 0.2, and two groups of dots have a ratio of 10:12, you have a 75% chance of telling which is larger.

For numerosity, your ability to detect differences is proportional to the size of the stimulus, not the absolute value. Your ability to disitinguish 20 from 40 is the same as your ability to distinguish 200 from 400. In fewer words, you notice percent differences, not absolute differences.

There is a very weak correlation, roughly r = -.2, between intelligence and Weber fraction, and the typical adult Weber fraction is around .15-.25, with wide variation. You can test yours below!

Two groups of dots appear briefly. Judge which side has more. Press F for left, J for right. On mobile, use the buttons.