Two digits appear at different physical sizes. Quickly judge which digit is numerically larger while ignoring their physical size. The conflict between physical and numerical magnitude reveals the size-congruity effect (Besner & Coltheart, 1979).
Very Easy
Digits 1-5, 20 trials, 3s limit, high size contrast
Easy
Digits 1-7, 24 trials, 2.5s limit
Medium
Digits 1-9, 28 trials, 2s limit
Hard
Digits 1-9, 32 trials, 1.5s limit, subtle size difference
Expert
Digits 1-9, 36 trials, 1.2s limit, minimal size contrast
Scientific Background
Based on: Numerical Stroop / Size-Congruity Effect (Besner & Coltheart, 1979; Henik & Tzelgov, 1982) (Besner et al., 1979)