Numerical Stroop Task

The Numerical Stroop task (also known as the Size Congruency task) measures the automatic processing of numerical magnitude and its interference with judgements of physical size. Two numbers are presented side-by-side, one larger in font size than the other. Participants judge which number is physically larger while ignoring the numerical values.

The key manipulation is congruence: on congruent trials the numerically larger number is also physically larger (e.g., a large-font "8" next to a small-font "2"). On incongruent trials the physically larger number is numerically smaller (e.g., a large-font "2" next to a small-font "8"). Reaction times are typically slower and error rates higher on incongruent trials — the size congruency effect — reflecting automatic activation of numerical magnitude during a purely perceptual task.

This paradigm is widely used in research on numerical cognition, mathematical learning disabilities, and the mental number line. This implementation follows the design described by Henik & Tzelgov (1982), includes a short mixed practice block (congruent and incongruent trials with correct/incorrect feedback), and runs 24 balanced main trials. All timing and display parameters are configurable in the Open Lab study builder.