Leask S J, Crow T J
Prince of Wales International Centre, Department of Psychiatry, Warneford Hospital, Oxford, U.K.
Neuropsychologia. 1997 Oct;35(10):1381-7. doi: 10.1016/s0028-3932(97)00059-6.
The relationship between measures (of size or function) on one side of the brain, in relation to the difference between the two sides on that measure, are important components of theories of hemispheric asymmetry. For example, it has been concluded that increasing lateralization (e.g., of hand skill or planum temporale area) occurs at the expense of the non-dominant hemisphere. Here it is demonstrated that such relationships could merely be a necessary consequence of relating components of a laterality index to the index (L - R)/(L + R) itself, or indeed to L - R. An alternative approach (using random data to exemplify the null hypothesis) is presented together with an application to data on hand skill from 12,782 11-year-olds in a cohort study. This demonstrates a symmetry hitherto undocumented of maximal hand skill in left and right hands in left- and right-hand writers respectively, the point of the maximum falling short of the population mean for relative hand skill in either case. If degrees of laterality are what is genetically determined, this suggests that selection is present for a function (perhaps language) associated with a greater magnitude of lateralization than is represented by hand skill.
大脑一侧（大小或功能方面）的测量指标与该指标两侧差异之间的关系，是半球不对称性理论的重要组成部分。例如，已得出结论：侧化增强（如手部技能或颞平面区域的侧化）是以非优势半球为代价的。本文证明，此类关系可能仅仅是将利手指数的各组成部分与指数（L - R）/（L + R）本身，或者实际上与L - R相关联的必然结果。本文还提出了一种替代方法（使用随机数据来例证零假设），并将其应用于一项队列研究中12782名11岁儿童的手部技能数据。这表明，在该队列研究中，左手写字者和右手写字者的左右手可达到的最大手部技能分别存在一种此前未被记录的对称性，在这两种情况下，最大技能点均低于总体相对手部技能的平均值。如果侧化程度是由基因决定的，这表明存在对一种功能（可能是语言）的选择，该功能所关联的侧化程度大于手部技能所代表的侧化程度。
