Primitives and Non-primitives of Numerical Representations

Primitives of numerical representation are numbers holistically represented on the mental number line (MNL). Non-primitives are numbers generated from primitives in order to perform specific tasks. Primitives can be automatically retrieved from long-term memory (LTM). Using the size congruency effect in physical comparisons as a marker of automatic retrieval, and its modulation by intrapair numerical distance as an indication of alignment along the MNL, we identify single-digits, but not two-digit numbers, as primitives. By the same criteria, zero is a primitive, but negative numbers are not primitives, which makes zero the smallest numerical primitive. Due to their unique notational structure, fractions are automatically perceived as smaller than 1. While some specific, familiar unit fractions may be primitives, this can be shown only when component bias is eliminated by training participants to denote fractions by unfamiliar figures.