Semantic Diversity Accounts for the "Missing" Word Frequency Effect in Stroke Aphasia: Insights Using a Novel Method to Quantify Contextual Variability in Meaning
Semantic Diversity Accounts for the "Missing" Word Frequency Effect in Stroke Aphasia: Insights Using a Novel Method to Quantify Contextual Variability in Meaning
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DOI：
10.1162/jocn.2011.21614
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发表时间：
2011-09-01
影响因子：
3.2
通讯作者：
Ralph, Matthew A. Lambon
中科院分区：
文献类型：
--
作者：
Hoffman, Paul;Rogers, Timothy T.;Ralph, Matthew A. Lambon
词频是健康个体和计算模型中语言处理效率的有力预测因素。令人困惑的是，频率效应在中风失语症中往往不存在，这挑战了词频影响任何计算系统行为的假设。为了解决这个难题，我们调查了两个理解障碍患者组的频率的不同影响。语义性痴呆患者由于前颞叶萎缩导致概念知识退化，并表现出强烈的频率效应。相比之下，中风后多模态语义障碍（语义性失语[SA]）的患者表现出很少或没有频率效应。他们的缺陷源于控制过程受损，使激活偏向与任务相关的知识方面。我们假设高频词对认知控制的要求更高，因为它们的语义更多样它们往往出现在更广泛的语言环境中，具有更多的可变含义。利用潜在语义分析，我们开发了一种新的衡量语义多样性的方法，反映了一个词的含义在不同语境中的变化。频率，但不是多样性，是一个重要的预测语义性痴呆的理解，而多样性是最好的预测性能在SA。最重要的是，SA患者表现出典型的频率效应，但只有当多样性的影响被考虑在内。这些结果是一致的，认为高频词对控制过程提出了更高的要求，因此，当控制过程被破坏时，与高频词相关的内在处理优势被掩盖了。
Word frequency is a powerful predictor of language processing efficiency in healthy individuals and in computational models. Puzzlingly, frequency effects are often absent in stroke aphasia, challenging the assumption that word frequency influences the behavior of any computational system. To address this conundrum, we investigated divergent effects of frequency in two comprehension-impaired patient groups. Patients with semantic dementia have degraded conceptual knowledge as a consequence of anterior temporal lobe atrophy and show strong frequency effects. Patients with multimodal semantic impairments following stroke (semantic aphasia [SA]), in contrast, show little or no frequency effect. Their deficits arise from impaired control processes that bias activation toward task-relevant aspects of knowledge. We hypothesized that high-frequency words exert greater demands on cognitive control because they are more semantically diverse-they tend to appear in a broader range of linguistic contexts and have more variable meanings. Using latent semantic analysis, we developed a new measure of semantic diversity that reflected the variability of a word's meaning across different context. Frequency, but not diversity, was a significant predictor of comprehension in semantic dementia, whereas diversity was the best predictor of performance in SA. Most importantly, SA patients did show typical frequency effects but only when the influence of diversity was taken into account. These results are consistent with the view that higher-frequency words place higher demands on control processes, so that when control processes are damaged the intrinsic processing advantages associated with higher-frequency words are masked.