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From early in life, people implicitly associate time, number, and other abstract conceptual domains with space. Accord- ing to the Generalized Magnitude System proposal, these men- tal mappings reflect a common neural system for represent- ing various magnitudes, and share a common spatial organiza- tion. In a test of this proposal, here we measured mappings of size, time, and number in the Tsimane’, an indigenous Ama- zonian group with few of the cultural practices (like reading and math) that spatialize size, time, and number in the expe- rience of industrialized adults. On three spatial axes, the Tsi- mane’ systematically arranged imagistic stimuli according to their magnitudes, but they showed no directional preferences overall and individuals often mapped different domains in op- posite directions. The results are inconsistent with predictions of the Generalized Magnitude System proposal but can be ex- plained by Hierarchical Mental Metaphor Theory, according to which mental mappings initially reflect a set of correlations observable in the natural world. 

In industrialized groups, adults implicitly map numbers, time, and size onto space according to cultural practices like reading and counting (e.g., from left to right). Here, we tested the mental mappings of the Tsimane’, an indigenous population with few such cultural practices. Tsimane’ adults spatially arranged number, size, and time stimuli according to their relative magnitudes but showed no directional bias for any domain on any spatial axis; different mappings went in different directions, even in the same participant. These findings challenge claims that people have an innate left-to-right mapping of numbers and that these mappings arise from a domain-general magnitude system. Rather, the direction-specific mappings found in industrialized cultures may originate from direction-agnostic mappings that reflect the correlational structure of the natural world.