Abstract
Humans exhibit exclusive complex arithmetic abilities, which are attributed to our exceptionally large neocortex. However, ubiquitous-primitive mechanisms (i.e., subcortical) are involved in basic numerical abilities both in humans and other species. Those basic numerical skills are the foundation for humans’ advanced arithmetic abilities. Hence, the remaining outstanding question is whether subcortical brain regions are not only involved in rudimentary numerical skills but also have a functional role in complex arithmetic calculations? In four different experiments, we explored whether primitive monocular (mostly subcortical) channels have a functional role in arithmetic calculations. Participants did a verification task in which they were asked to evaluate arithmetical statements composed of three digits and a solution (e.g., 9−5−3=1) as either correct or incorrect. Using a stereoscope, the equations were displayed in three Numbers eye-of-origin conditions: (i) the whole equation was presented to a single eye or (ii) the calculation term (left side of the equation) was presented to one eye and the solution to a different eye or (iii) one digit of the calculation term was presented to a different eye than the rest of the digits. The pattern of results demonstrates that presenting one digit of the calculation term to a different eye hamper performance. In contrast to most literature, the current findings provide a converging evidence for the causal relation between a unique human cultural product, such as arithmetic calculations abilities, and primitive-ubiquitous subcortical brain regions. We propose that human’s complex arithmetic abilities are founded upon lower evolutionarily ancient brain circuits.