Direction effects in number word comparison: an event-related potential study

Event-related potentials were recorded to investigate the effects of direction on number word comparison. Participants saw a sequence of two number words, and next indicated whether the second number word denoted a quantity smaller or larger than the first number word, depending on the nature of the prompt. Faster and more accurate responses were obtained at the prompt for increasing number sequences than for decreasing number sequences. Event-related potentials to the second number word showed an enhanced positivity for increasing sequences. This confirms the view that numbers are mentally represented on a number line, with smaller numbers appearing before larger numbers. Direction of presentation should therefore be taken into consideration when designing studies on numerical processing.