Department of Linguistics, Harvard University, Cambridge, Massachusetts, United States of America.
PLoS One. 2013;8(3):e59103. doi: 10.1371/journal.pone.0059103. Epub 2013 Mar 27.
We report data from an internet questionnaire of sixty number trivia. Participants were asked for the number of cups in their house, the number of cities they know and 58 other quantities. We compare the answers of familial sinistrals--individuals who are left-handed themselves or have a left-handed close blood-relative--with those of pure familial dextrals--right-handed individuals who reported only having right-handed close blood-relatives. We show that familial sinistrals use rounder numbers than pure familial dextrals in the survey responses. Round numbers in the decimal system are those that are multiples of powers of 10 or of half or a quarter of a power of 10. Roundness is a gradient concept, e.g. 100 is rounder than 50 or 200. We show that very round number like 100 and 1000 are used with 25% greater likelihood by familial sinistrals than by pure familial dextrals, while pure familial dextrals are more likely to use less round numbers such as 25, 60, and 200. We then use Sigurd's (1988, Language in Society) index of the roundness of a number and report that familial sinistrals' responses are significantly rounder on average than those of pure familial dextrals. To explain the difference, we propose that the cognitive effort of using exact numbers is greater for the familial sinistral group because their language and number systems tend to be more distributed over both hemispheres of the brain. Our data support the view that exact and approximate quantities are processed by two separate cognitive systems. Specifically, our behavioral data corroborates the view that the evolutionarily older, approximate number system is present in both hemispheres of the brain, while the exact number system tends to be localized in only one hemisphere.
我们报告了六十个数字 trivia 的互联网问卷数据。参与者被要求提供他们家里杯子的数量、他们知道的城市数量以及其他 58 个数量。我们比较了家族左撇子（自己是左撇子或有左撇子近亲的个体）和纯粹家族右撇子（报告只有右撇子近亲的个体）的答案。我们表明，在调查回答中，家族左撇子使用的圆形数字比纯粹家族右撇子多。十进制系统中的圆形数字是那些 10 的倍数或 10 的一半或四分之一的倍数。圆形是一个渐变的概念，例如 100 比 50 或 200 更圆。我们表明，像 100 和 1000 这样非常圆的数字被家族左撇子使用的可能性比纯粹家族右撇子高 25%，而纯粹家族右撇子更有可能使用不太圆的数字，如 25、60 和 200。然后，我们使用 Sigurd（1988，Language in Society）的数字圆度指数，并报告说，家族左撇子的回答平均比纯粹家族右撇子的回答更圆。为了解释这种差异，我们提出，家族左撇子组使用精确数字的认知努力更大，因为他们的语言和数字系统往往更分布在大脑的两个半球上。我们的数据支持这样一种观点，即精确和近似的数量是由两个独立的认知系统处理的。具体来说，我们的行为数据证实了这样一种观点，即进化上更早的近似数量系统存在于大脑的两个半球中，而精确数量系统往往局限于一个半球中。
