Skarratt Paul A, Lavidor Michal
Department of Psychology, University of Hull, UK.
J Cogn Neurosci. 2006 Oct;18(10):1749-58. doi: 10.1162/jocn.2006.18.10.1749.
One of the hallmarks of expert reading is the ability to identify arrays of several letters quickly and in parallel. Such length-independent reading has only been found for word stimuli appearing in the right visual hemifield (RVF). With left hemifield presentation (LVF), response times increase as a function of word length. Here we investigated the comparative efficiency with which the two hemispheres are able to recognize visually presented words, as measured by word length effects. Repetitive transcranial magnetic stimulation (rTMS) of the left occipital cortex disrupted expert processing of the RVF such that a length effect was created (Experiment 1). Right occipital rTMS, on the other hand, had no such effect on RVF words and nor did it modulate the length effect already present in the LVF. Experiment 2 explored the time course of these TMS-induced effects by applying single pulses of TMS at various stimulus-onset asynchronies for the same task. We replicated the TMS-induced length effect for RVF words, but only when a single pulse was applied to the left visual cortex 80 msec after target presentation. This is the first demonstration of TMS-induced impairment producing a word length effect, and as such confirms the specialization of the left hemisphere in word recognition. It is likely that anatomical differences in the pathway linking retinal input to higher level cortical processing drive this effect.
专家阅读的一个标志是能够快速且并行地识别几个字母的组合。这种与长度无关的阅读仅在右视野（RVF）中出现的单词刺激中被发现。当单词呈现在左视野（LVF）时，反应时间会随着单词长度的增加而延长。在这里，我们通过单词长度效应来研究两个半球识别视觉呈现单词的相对效率。对左侧枕叶皮质进行重复经颅磁刺激（rTMS）会干扰右视野的专家级处理，从而产生长度效应（实验1）。另一方面，右侧枕叶rTMS对右视野单词没有这种影响，也没有调节左视野中已存在的长度效应。实验2通过在相同任务中以不同的刺激起始异步施加单个TMS脉冲，探索了这些TMS诱导效应的时间进程。我们复制了rTMS对右视野单词产生的长度效应，但只有在目标呈现后80毫秒对左侧视觉皮质施加单个脉冲时才会出现这种效应。这是首次证明TMS诱导的损伤会产生单词长度效应，从而证实了左半球在单词识别中的特异性。视网膜输入与更高层次皮质处理之间的通路在解剖结构上的差异可能导致了这种效应。
