Abstract: When using fraction knowledge, children often use previously formed single-unit counting scheme to interpret the fractions. This phenomenon named as “whole number bias” is ubiquitous in fractional cognition. Researchers have explained its genesis from the point of innate and acquired, basing on the hypothesis of innate constraint, undifferentiated amount, and learning account. Most studies used pencil-and-paper test and verbal report to investigate the whole number bias. However, in recent studies mental number line hypothesis appeared as a useful instrument to study adult’s whole number bias. In this area, there are four chief prospects for the future research: clarifying the concept, exploring the origin of bias, extending the research methods and strengthening interventional research.

Key words: whole number bias, fractional cognition, mental number line