Department of Psychology and York Neuroimaging Centre, University of York, Heslington, York YO10 5DD, UK.
Neuropsychologia. 2012 Jul;50(8):1968-79. doi: 10.1016/j.neuropsychologia.2012.04.022. Epub 2012 May 8.
Patients with multimodal semantic impairment following stroke (referred to here as 'semantic aphasia' or SA) fail to show the standard effects of frequency in comprehension tasks. Instead, they show absent or even reverse frequency effects: i.e., better understanding of less common words. In addition, SA is associated with poor regulatory control of semantic processing and executive deficits. We used a synonym judgement task to investigate the possibility that the normal processing advantage for high frequency (HF) words fails to emerge in these patients because HF items place greater demands on executive control. In the first part of this study, SA patients showed better performance on more imageable as opposed to abstract items, but minimal or reverse frequency effects in the same task, and these negative effects of word frequency on comprehension were related to the degree of executive impairment. Ratings from healthy subjects indicated that it was easier to establish potential semantic associations between probe and distracter words for HF trials, suggesting that reverse frequency effects might reflect a failure to suppress spurious associations between HF probes and distracters. In a subsequent experiment, the aphasic patients' performance improved when HF probes and targets were presented alongside low frequency distracters, supporting this hypothesis. An additional study with healthy participants used dual task methodology to examine the impact of divided attention on synonym judgement. Although frequently encountered words were processed more efficiently overall, the secondary task selectively disrupted performance for high but not low frequency trials. Taken together, these results show that positive effects of frequency are counteracted in SA by increases in semantic control requirements for HF words.
脑卒中后多模态语义障碍患者（这里称为“语义性失语症”或 SA）在理解任务中无法表现出频率的标准效应。相反，他们表现出缺失甚至相反的频率效应：即，对不太常见的单词有更好的理解。此外，SA 与语义处理的不良调节控制和执行功能缺陷有关。我们使用同义词判断任务来研究高频（HF）词的正常处理优势在这些患者中未能出现的可能性，因为 HF 项对执行控制的要求更高。在这项研究的第一部分，SA 患者在更具形象性的项目上表现优于更抽象的项目，而在相同任务中几乎没有或出现相反的频率效应，并且这种词频对理解的负面影响与执行功能障碍的程度有关。健康受试者的评分表明，对于 HF 试验，更容易在探针和分心词之间建立潜在的语义关联，这表明相反的频率效应可能反映了 HF 探针和分心词之间的虚假关联无法被抑制。在随后的实验中，当 HF 探针和目标与低频分心词一起呈现时，失语症患者的表现得到了改善，支持了这一假设。一项针对健康参与者的额外研究使用双重任务方法来检查注意力分散对同义词判断的影响。尽管高频词总体上处理效率更高，但次要任务选择性地破坏了高频而非低频试验的表现。综上所述，这些结果表明，在 SA 中，HF 词的语义控制要求增加会抵消频率的积极影响。
