Numerical Stroop Effect

The numerical Stroop effect is the interference that occurs when a person compares two digits' numerical value or their physical size and the two dimensions conflict, such as a physically larger 3 printed beside a physically smaller 5; reaction times slow when size and value disagree and speed up when they agree. Unlike the classic color-word Stroop effect, in which color naming is disrupted by an incongruent word more than word reading is disrupted by an incongruent color, the numerical version produces roughly symmetrical interference, with irrelevant size and irrelevant numerical value each slowing the other's judgment about equally, which researchers take as evidence the two dimensions are processed in parallel. The effect persists even when a person is told to ignore one of the two dimensions, indicating that number processing of this kind is automatic, and brain-imaging studies point to the intraparietal sulcus as a key region, with children's growing familiarity with numerical symbols affecting how strongly the effect appears as they develop.