Stanislas Dehaene, Véronique Izard, Elizabeth Spelke, and Pierre Pica. Log or linear? Distinct intuitions of the number scale in Western and Amazonian indigene cultures. Science, 320(5880):1217–1220, May 2008.
The Mundurucu are an indigenous culture whose language does not contain exact words for numbers above 5. Dehaene, Izard, Spelke, and Pica basically gave subjects an empty horizontal line and then gave them a bunch of numbers and told them to place the numbers where they belong on the line (the line was not entirely empty; the left and right hand sides were labeled with a small number and a big number).
Western adults tend to place the numbers linearly, whereas the Mundurucu tend to place them logarithmically. Western children also place them logarithmically, and even Western adults place them logarithmically if the numbers are presented as larger numbers of dots (10-100) or if they are presented as tones.
This suggests that there is an innate logarithmic representation of number which is used to populate the number line, but that with training a linear representation can be created.