Mental Number Line

The speed of processing in simple number tasks, such as magnitude comparison (“which number is larger?”), reveals much about the cognitive representation of numbers. Three effects, in particular, point to a “mental number line” as the universal representation of number meaning in our minds. First, we usually find that the time to discriminate two numbers decreases with increasing numerical distance between them: we know that 8 is larger than 2 before we know that 4 is larger than 2. This distance effect holds regardless of number format (digits, words, dot patterns, Roman numerals), stimulus modality (visual, auditory), or response modality (verbal, button press). Second, if we hold the distance between numbers constant (as in the pairs 4 − 2 vs. 8 − 6) we need less time to process small than large numbers, and are also more accurate (the size effect). Finally, varying their spatial arrangement (4 − 2 vs. 2 − 4) often reveals faster responses with smaller numbers on the left and larger numbers on the right side. This spatial-numerical association of response codes (SNARC) effect does, however, depend on cultural factors. Keywords: cognition; problem solving