Date of Award




First Advisor

David F. Sherry

Second Advisor

Caroline G. Strang


The estimation of number by humans shows evidence for a mental number line in which magnitude increases from left to right. Rugani, Vallortigara, Priftis, and Regolin (2015) recently reported a similar mental number line in domestic chicks. This is an unexpected result given the role of language and culture in the human mental number line. Animals do not possess language or arithmetic concepts like the mental number line. Because the results reported by Rugani et al. (2015) seem improbable from this perspective, my study sought to determine whether the observations of Rugani et al. (2015) occur reliably. I tested for the occurrence of a mental number line in domestic chicks following as closely as possible the procedure described by Rugani et al. (2015). Domestic chicks were trained and tested for left / right preferences in a food-rewarded choice task. Chicks were trained to find food behind an opaque panel with varying arrangements of 5 red squares. Two identical panels with the same number of red squares on each were presented in each test. The number of squares was either large or small compared to the number of squares the chicks had seen on a sample panel. The prediction was that if the number on the test panels was small compared to the sample, chicks would choose left and if it was large chicks would choose right. The chicks showed no left / right preference. I found no evidence that a mental number line plays a role in domestic chicks’ numerical abilities.