The integers include more structure than the natural numbers; for example, they exhibit symmetry about zero. Do adult mental representations directly encode this increased structure? In two studies, adults completed a numerical bi-section task in which they were presented with two symbolic integers and were asked to report the digit at the midpoint of the interval. The reaction times demonstrated a tuning curve such that people were faster when the midpoint or end point of an interval was close to zero. The results suggest that the mental representation of negative numbers and zero has incorporated analog properties to represent the increased structure of the integers.