When you think of the numbers 1–10, you probably envision them running along a line, with 1 on the left and 10 on the right. Scientists have long debated whether this tendency is hardwired or culturally instilled. This week, the hardwired camp scored a major point. Young chickens, it seems, also map numbers from left to right.
Photo Credit: Rosa Rugani, University of Padova
The chicks, trained to seek out mealworms behind white plastic panels printed with varying numbers of identical red squares, repeatedly demonstrated a preference for the left when the number of squares was small and for the right when the number was larger...
In their report, [researchers led by University of Padova psychologist Rosa Rugani] said the findings supported the idea that the left-right orientation for numbers is innate rather than determined by culture or education... the new research, Dr. Rugani and her colleagues wrote, indicates that orienting numbers in space may represent "a universal cognitive strategy available soon after birth."
The video above demonstrates the setup of one of the experiments. The majority of chicks familiarized with the number 20 wander to the left when presented with panels depicting a relatively smaller value of 8, but gravitate to the right when the panels display a relativelylarger value of 32. You can read the details behind the experiment, which was really quite cleverly conducted, at the NYT.
The results of the study, which appear in this week's issue of Science, add to a growing pile of conflicting data in the debate over innate versus learned number-mapping. Back in 2012, researchers concluded that members of a remote tribe in Papua New Guinea do not intuitively map numbers along a line (despite understanding the concept of numbers), suggesting that the idea of a number line is actually a cultural construct – a metaphor devised to aid with numeracy. The findings seemed to contradict with conclusions drawn in 2002, when researchers discovered that test subjects with brain damage that prevented them from perceiving one side of the body struggled to identify the midpoint of a numerical interval when asked to "bisect" it, claiming, for instance, that five is halfway between two and six. This observation, the researchers reported in the journal Nature, "constitutes strong evidence that the mental number line is more than simply a metaphor, and that its spatial nature renders it [functionally similar] to physical lines."
There is also evidence that our tendency to map numbers in space is the result of culture acting on some inborn quality, i.e. a case of nature conspiring with nurture. In 2008, a study published in the journal Science found that the Mundurucu, an indigenous group in the Amazon with little-to-no formal education, map numbers linearly, but do so on a logarithmic scale, rather than a linear one. A year later, another team of researchers found test subjects who read both English words and Arabic numbers from left to right map small to large numbers from left to right, but that test subjects who read Arabic words and Arabic-Indic numbers from right to left "showed the reverse association." These findings suggested that the number line itself may be hard-wired, and that it is instead the line's quality – its scale, in this instance, or its directionality – that is culturally crafted.