# Without Counting: How Many Dots Can You Catch in a Quarter of a Second?

Watch the optical shutter open in the HTML edition, then call how many dots were there. A six-round experiment with a 250-millisecond exposure that measures the boundary between instant recognition (subitizing) and numerical estimation.

[Open interactive experiment](https://mariuscomper.uk/fara-sa-numeri/en/)

## How it works

1. Press the "Watch" button or tap Spacebar.
2. The mechanical leaf shutter snaps open for exactly 250 milliseconds, displaying a scatter of dots (between 3 and 8).
3. The shutter snaps shut. Select the number of dots you saw (3 through 9).
4. Receive an immediate verdict and signed error.
5. After six rounds, receive your complete Tachistogram: glance threshold, mean error, and visual estimation bias.

## Scientific basis

For three or four dots, the human brain does not count: it recognizes quantity in parallel (subitizing). Above four dots, vision requires rapid eye saccades (which take at least 200 milliseconds to initiate). In a 250-millisecond glance, saccades cannot happen, forcing the brain into approximate estimation.

Text and implementation: Marius Comper, 3 September 2026.