The Evolution and Development of Spatial-Numerical Association: A Comparative Review

Humans and animals share basic abilities to represent numerosity, called number sense, which underpins human abstract numerical skills. A key feature is Spatial-Numerical Association (SNA): the association of small numbers with the left and large ones with the right space. Initially observed in human adults using symbolic numbers, SNA has been found in newborns and animals using non-symbolic numerosity. This discovery initiated a debate on the SNA's origins: Is the use of space to represent numbers a learning outcome or an inherited predisposition? This review presents an up-to-date, comprehensive overview on systematic developments in SNA. Specifically, it 1) organizes the present literature by tracing back the emergence of SNA in humans, primates, birds and invertebrates; 2) outlines SNA modulation over the lifespan; 3) critically compares the most influential models regarding the origin and modulation of SNA; 4) expands the focus by providing evidence on SNA in arithmetic; 5) suggests future research directions. From this comprehensive overview, it emerges that a biological predisposition to associate numerosity with space is inherent in nervous systems endowed with a number sense, irrespective of their neural complexity. Strength and orientation of SNA are then modulated by ontogenetic aspects and adapted to solve contingent problems. Importantly, SNA plays a crucial role in mathematical cognition. This holistic understanding of how SNA emerges, evolves and adapts provides a new perspective from which to refine both the conceptual and methodological definitions of SNA, with important implications for the development of efficient mathematical brains.