Grey Sarah, Tanner Darren, van Hell Janet G
Department of Modern Languages and Literatures, Fordham University, Faber Hall 556, Bronx, NY 10458, USA.
Department of Linguistics, University of Illinois at Urbana-Champaign, 707 S. Mathews Avenue, Urbana, IL 61801, USA; Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, 707 S. Mathews Avenue, Urbana, IL 61801, USA.
Brain Res. 2017 Aug 15;1669:27-43. doi: 10.1016/j.brainres.2017.05.024. Epub 2017 May 26.
Most neurocognitive models of language processing generally assume population-wide homogeneity in the neural mechanisms used during language comprehension, yet individual differences are known to influence these neural mechanisms. In this study, we focus on handedness as an individual difference hypothesized to affect language comprehension. Left-handers and right-handers with a left-handed blood relative, or familial sinistrals, are hypothesized to process language differently than right-handers with no left-handed relatives (Hancock and Bever, 2013; Ullman, 2004). Yet, left-handers are often excluded from neurocognitive language research, and familial sinistrality in right-handers is often not taken into account. In the current study we used event-related potentials to test morphosyntactic processing in three groups that differed in their handedness profiles: left-handers (LH), right-handers with a left-handed blood relative (RH FS+), and right-handers with no reported left-handed blood relative (RH FS-; both right-handed groups were previously tested by Tanner and Van Hell, 2014). Results indicated that the RH FS- group showed only P600 responses during morphosyntactic processing whereas the LH and RH FS+ groups showed biphasic N400-P600 patterns. N400s in LH and RH FS+ groups are consistent with theories that associate left-handedness (self or familial) with increased reliance on lexical/semantic mechanisms during language processing. Inspection of individual-level results illustrated that variability in RH FS- individuals' morphosyntactic processing was remarkably low: most individuals were P600-dominant. In contrast, LH and RH FS+ individuals showed marked variability in brain responses, which was similar for both groups: half of individuals were N400-dominant and half were P600-dominant. Our findings have implications for neurocognitive models of language that have been largely formulated around data from only right-handers without accounting for familial sinistrality or including left-handers, and moreover highlight that there is systematic - and often ignored - variability in language processing outcomes in neurologically healthy populations.
大多数语言处理的神经认知模型通常假定在语言理解过程中所使用的神经机制在人群中具有同质性，但已知个体差异会影响这些神经机制。在本研究中，我们聚焦于用手习惯这一个体差异，假设它会影响语言理解。据推测，左利手以及有左利手血亲的右利手（即家族性左利手）在语言处理方式上与没有左利手亲属的右利手不同（汉考克和贝弗，2013年；乌尔曼，2004年）。然而，左利手个体常常被排除在神经认知语言研究之外，而且右利手中的家族性左利手情况也常常未被考虑在内。在当前研究中，我们使用事件相关电位来测试三组用手习惯不同的人群的形态句法处理情况：左利手（LH）、有左利手血亲的右利手（RH FS+）以及没有报告有左利手血亲的右利手（RH FS-；两个右利手组先前已由坦纳和范·赫尔测试过，2014年）。结果表明，RH FS-组在形态句法处理过程中仅表现出P600反应，而LH组和RH FS+组表现出双相的N400 - P600模式。LH组和RH FS+组中的N400与将左利手（自身或家族性）与语言处理过程中对词汇/语义机制的更多依赖联系起来的理论相一致。对个体层面结果的检查表明，RH FS-个体在形态句法处理方面的变异性非常低：大多数个体以P600为主。相比之下，LH个体和RH FS+个体在大脑反应方面表现出明显的变异性，两组情况相似：一半个体以N400为主，另一半以P600为主。我们的研究结果对主要基于仅来自右利手的数据、未考虑家族性左利手情况或未纳入左利手个体而构建的语言神经认知模型具有启示意义，并且进一步凸显出在神经健康人群的语言处理结果中存在系统性的——且常常被忽视的——变异性。
