Brain lateralization is a fundamental aspect of the organization of brain and behavior in the animal kingdom, begging the question about its Darwinian function. We tested the possibility that lateralization enhances cognitive performance in single- and dual-tasks. Previous studies reported mixed results on this topic and only a handful of studies have measured functional brain lateralization and performance independently and simultaneously. We therefore examined a possible positive effect of the strength and direction of lateralization on two demanding cognitive tasks: A visuospatial task (mental rotation MR), and a language task (word generation WG), executed either as a singletask or as dual-task. Participants (n = 72) performed these tasks while their single-task brain lateralization was assessed with functional Transcranial Doppler for both tasks. From these measurements we determined strength and direction of lateralization for both tasks and the individual pattern of lateralization (contralateral or ipsilateral) was derived. These factors, along with sex, were used in a GLM analysis to determine if they predicted the respective performance measure of the tasks. We found that for MR there was a significant medium effect of direction of lateralization on performance with better performance in left-lateralized (atypical) participants (partial eta squared 0.061; p = .039). After correction for outliers, there was a significant effect for strength (p = .049). For the dual-task, there was a significant positive medium effect of strength of lateralization on performance (partial eta squared 0.062; p = .038, respectively) No other association between direction or strength in either tests were found. We conclude that there is no evidence for hemispheric crowding, and that strength of lateralization may be a factor that contributes to the evolutionary selection of functional brain lateralization. Pattern of lateralization does not, explaining the large inter-individual variation in these traits.

大脑偏侧化是动物界大脑和行为组织的一个基本方面，这就引出了有关其达尔文功能的问题。我们测试了侧化提高单任务和双任务认知能力的可能性。以前的研究报告了关于这个主题的混合结果，只有少数研究独立和同时测量了功能性大脑侧化和性能。因此，我们研究了侧化的强度和方向对两个要求苛刻的认知任务可能产生的积极影响：视觉空间任务（心理旋转 MR）和语言任务（单词生成 WG），作为单任务或双任务执行。参与者 (n = 72) 执行这些任务，同时使用功能性经颅多普勒对这两项任务评估他们的单任务大脑侧化。根据这些测量，我们确定了两个任务的侧化强度和方向，并推导出了单个侧化模式（对侧或同侧）。这些因素与性别一起用于 GLM 分析，以确定它们是否预测了任务的相应性能指标。我们发现，对于 MR，偏侧化方向对表现有显着的中等影响，在左侧（非典型）参与者中表现更好（部分 eta 平方 0.061；p = .039）。校正异常值后，强度有显着影响 (p = .049)。对于双重任务，侧化强度对表现有显着的积极中等影响（部分 eta 平方 0.062；分别为 p = .038） 在任一测试中都未发现方向或力量之间存在其他关联。我们得出结论，没有半球拥挤的证据，并且侧化的强度可能是促成功能性大脑侧化进化选择的一个因素。侧化模式没有，解释了这些性状的巨大个体间差异。侧化的强度可能是促成功能性大脑侧化进化选择的一个因素。侧化模式没有，解释了这些性状的巨大个体间差异。侧化的强度可能是促成功能性大脑侧化进化选择的一个因素。侧化模式没有，解释了这些性状的巨大个体间差异。