The human brain has a remarkable capacity to focus processing resources based on the features and the relevance of the task at hand. The two cerebral hemispheres contribute differentially to this capacity, with the left hemisphere linguistic and right hemisphere visuo-spatial abilities each offering unique contributions. For example, previous research has established that healthy participants set the subjective mid-point of written sentences more leftwards of center, compared to unpronounceable letter strings or simple lines. Remarkably, patients with right hemisphere damage exhibiting unilateral spatial neglect also show this pattern, even though, as well known in the literature, they tend toward a rightward- bias for non-linguistic stimuli. This evidence suggests that the leftward bias for sentential material is due to linguistic, mainly left-hemisphere mediated processes, which are largely unimpaired in right brain-damaged patients, and intact in heathy participants. To test this hypothesis, we compared sentence bisection performance to that of letter strings and simple lines in left brain-damaged patients (with and without aphasia). If the larger leftward bias in the bisection of sentential material is based on linguistic processes, then the left brain-damaged patients should show a reduction or absence of a leftward bias in sentence bisection. We tested twenty-four left brain-damaged patients (12 with aphasia and 12 without aphasia), and 24 age-matched elderly participants (patients and controls were all right-handed). Participants were asked to bisect 240 stimuli, comprising: (i) affirmative and interrogative clauses, (ii) sentences with lexical and syntactic violations, (iii) letter strings and (iv) simple lines. As predicted, neurologically intact participants showed larger leftward biases in bisecting written readable sentences compared to strings of letters. In contrast, the left hemispheredamaged patients (both with and without aphasia) showed no differences in bisecting sentences and letter strings or lines. These findings indicate that the larger leftward bias exhibited by healthy participants in the bisection of sentences is likely due to ortho-phonological coding taking place implicitly during the bisection task. This ortho-phonological coding is impaired with left brain damage - also in absence of apparent aphasia - leading to the left hemispheredamaged patients showing a reduced leftward bias in sentence bisection. These findings support the hypothesis that the leftward bias in the bisection of written sentences is the result of ortho-phonological influences rather than visual-spatial biases.

中文翻译：

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设置句子的中点：左半球的作用。

人脑具有基于手头任务的功能和相关性来集中处理资源的出色能力。两个大脑半球对此能力的贡献不同，左半球的语言能力和右半球的视觉空间能力各自提供了独特的贡献。例如，先前的研究已经确定，健康的参与者将书写句子的主观中点设置为比不发音的字母字符串或简单的线条更靠近中心的左侧。值得注意的是，右半球受损的患者表现出单方面的空间疏忽也显示出这种模式，尽管如文献所知，他们倾向于非语言刺激的右偏。该证据表明，句子材料的向左偏斜是由于语言，主要是左半球介导的过程，在受损的右脑患者中基本上没有受损，而健康的参与者则完整无缺。为了检验该假设，我们将左脑受损患者（有无失语症）的句子平分表现与字母和简单线条的表现进行了比较。如果句子材料的二等分中较大的左偏是基于语言过程，则左脑受损的患者应显示句子二等分中左偏的减少或不存在。我们测试了二十四名左脑受损的患者（12名失语症患者和12名无失语症患者），以及24名年龄相匹配的老年受试者（患者和对照组均为右手）。要求参与者将240个刺激一分为二，其中包括：（i）肯定和疑问条款，（ii）违反词汇和句法的句子，（iii）字母字符串和（iv）简单的行。如预期的那样，与字母串相比，神经完好的参与者在平分书面可读句子时显示出更大的左偏。相比之下，左半球受损的患者（有失语症和无失语症）在平分句子和字母或行时没有差异。这些发现表明，健康的参与者在二等分句子中表现出的更大的向左偏斜很可能是由于在二等分任务期间隐含地进行了正交语音编码。这种正交语音编码受左脑损伤的损害-甚至没有明显的失语症-导致左半球受损的患者在句子平分中显示出向左偏见的减少。