Abstract

Humans who use a left-to-right writing system often associate smaller numbers with the left side of space and larger numbers with the right. Whether this left-to-right number-space mapping is innate or culturally learned is unclear. Here, we test whether monkeys who lack human cultural practices show a left-to-right number-space mapping. Previous work in monkeys has found mixed evidence on whether monkeys show a left-to-right bias in their number-space mappings. Replicating the methods of Drucker and Brannon (2014), monkeys were trained to touch the fourth circle from the bottom in a vertical array of five circles. Then, they were tested with a horizontal array of five circles. Overall, monkeys showed no preference for the fourth circle from the left compared to the fourth from the right. This suggests monkeys may not have a directionality bias for number-space mappings. Therefore, the left-to-right bias in humans may be due to specific cultural practices.