Department of Psychology and York Neuroimaging Centre, University of York, York, YO10 5DD, UK.
Neuropsychologia. 2013 Aug;51(10):1998-2015. doi: 10.1016/j.neuropsychologia.2013.06.030. Epub 2013 Jul 10.
Research suggests that semantic memory deficits can occur in at least three ways. Patients can (1) show amodal degradation of concepts within the semantic store itself, such as in semantic dementia (SD), (2) have difficulty in controlling activation within the semantic system and accessing appropriate knowledge in line with current goals or context, as in semantic aphasia (SA) and (3) experience a semantic deficit in only one modality following degraded input from sensory cortex. Patients with SA show deficits of semantic control and access across word and picture tasks, consistent with the view that their problems arise from impaired modality-general control processes. However, there are a few reports in the literature of patients with semantic access problems restricted to auditory-verbal materials, who show decreasing ability to retrieve concepts from words when they are presented repeatedly with closely related distractors. These patients challenge the notion that semantic control processes are modality-general and suggest instead a separation of 'access' to auditory-verbal and non-verbal semantic systems. We had the rare opportunity to study such a case in detail. Our aims were to examine the effect of manipulations of control demands in auditory-verbal semantic, non-verbal semantic and non-semantic tasks, allowing us to assess whether such cases always show semantic control/access impairments that follow a modality-specific pattern, or whether there are alternative explanations. Our findings revealed: (1) deficits on executive tasks, unrelated to semantic demands, which were more evident in the auditory modality than the visual modality; (2) deficits in executively-demanding semantic tasks which were accentuated in the auditory-verbal domain compared with the visual modality, but still present on non-verbal tasks, and (3) a coupling between comprehension and executive control requirements, in that mild impairment on single word comprehension was greatly increased on more demanding, associative judgements across modalities. This pattern of results suggests that mild executive-semantic impairment, paired with disrupted connectivity from auditory input, may give rise to semantic 'access' deficits affecting only the auditory modality.
研究表明，语义记忆缺陷至少可以通过三种方式发生。患者可能会：(1) 在语义存储本身中表现出概念的无模态退化，例如在语义性痴呆（SD）中；(2) 在语义系统中难以控制激活并根据当前目标或上下文访问适当的知识，例如在语义性失语症（SA）中；(3) 在仅一种模态中出现语义缺陷，这是由于来自感觉皮层的输入降级。SA 患者在单词和图片任务中都表现出语义控制和访问的缺陷，这与他们的问题源于受损的模态通用控制过程的观点一致。然而，文献中有少数报道称，有些患者的语义访问问题仅限于听觉-口头材料，当他们反复呈现密切相关的干扰物时，他们从单词中检索概念的能力会逐渐下降。这些患者挑战了语义控制过程是模态通用的观点，并提出了听觉-口头和非口头语义系统之间的分离。我们有幸详细研究了这样一个案例。我们的目的是检查听觉-口头语义、非言语语义和非语义任务中控制需求的操作效果，使我们能够评估这些情况是否总是表现出遵循特定模式的语义控制/访问缺陷，或者是否存在替代解释。我们的发现揭示了：(1) 在听觉模态中比在视觉模态中更为明显的与语义需求无关的执行任务缺陷；(2) 在执行要求高的语义任务中存在缺陷，与视觉模态相比，在听觉-口头领域更为明显，但在非口头任务中仍然存在；(3) 理解和执行控制需求之间的耦合，即单字理解的轻度障碍在跨模态的更具挑战性的联想判断中大大增加。这种结果模式表明，轻度执行语义缺陷与听觉输入的连通性中断相结合，可能导致仅影响听觉模态的语义“访问”缺陷。
