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Spatial cognition is central to human behavior, but the way people conceptualize space varies within and across groups for unknown reasons. Here, we found that adults from an indigenous Bolivian group used systematically different spatial reference frames on different axes, according to known differences in their discriminability: In both verbal and nonverbal tests, participants preferred allocentric (i.e., environment-based) space on the left-right axis, where spatial discriminations (like “b” versus “d”) are notoriously difficult, but the same participants preferred egocentric (i.e., body-based) space on the front-back axis, where spatial discrimination is relatively easy. The results (i) establish a relationship between spontaneous spatial language and memory across axes within a single culture, (ii) challenge the claim that each language group has a predominant spatial reference frame at a given scale, and (iii) suggest that spatial thinking and language may both be shaped by spatial discrimination abilities, as they vary across cultures and contexts. 

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. 

Previous findings suggest that mentally representing exact numbers larger than four depends on a verbal count routine (e.g., “one, two, three . . .”). However, these findings are controversial because they rely on comparisons across radically different languages and cultures. We tested the role of language in number concepts within a single population—the Tsimane’ of Bolivia—in which knowledge of number words varies across individual adults. We used a novel data-analysis model to quantify the point at which participants ( N = 30) switched from exact to approximate number representations during a simple numerical matching task. The results show that these behavioral switch points were bounded by participants’ verbal count ranges; their representations of exact cardinalities were limited to the number words they knew. Beyond that range, they resorted to numerical approximation. These results resolve competing accounts of previous findings and provide unambiguous evidence that large exact number concepts are enabled by language. 

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.