语义范畴特异性损伤的理论研究进展

在对人类认知机制的研究中,以患者为研究对象是最近兴起的一种重要的认知神经科学手段.期间,人们发现有些脑损伤患者具有语义范畴特异性损伤现象,即表现出对个别语义范畴的认知能力相对较弱.这一奇特现象的发现,为研究人类的语义记忆系统的结构和功能开辟了一个全新的领域.该文着重介绍了这一现象及其引发的4种新的语义记忆理论,从而对人类的语义记忆作出重新审视.     

自然概念语义特征提取的范畴效应

本研究采用概念特征自由列举实验范式,考察三类范畴(动物、自然食物、人造物)自然概念的语义特征提取反应时间的范畴效应。结果表明,⑴语义特征提取的反应时间存在范畴效应:提取动物特征的时间显著短于提取自然食物特征的时间,提取自然食物特征的时间显著短于提取人造物特征的时间;⑵三类范畴的特征提取时间模式表现出相同的规律:先是显著降低(第1到第2个特征),然后持续升高(第2到第10个特征)。语义特征提取的范畴效应反映了语义记忆组织的范畴特异性,有必要进一步分析特征提取时间与特征类型、关联特征、独有特征之间的关系,以深入揭示语义特征提取范畴效应的产生机制。     

轻度认知损伤的语义记忆研究述评

轻度认知损伤（Mild cognitive impairment,MCI）是介于正常老化与痴呆之间的过渡阶段,表现为与年龄和教育程度不相称的认知功能减退。本文回顾了近期有关MCI语义记忆的研究,分析比较了各研究的实验任务及结果,得出MCI患者存在一定程度的由多种原因造成的语义记忆损伤,语义记忆测验对MCI的早期筛查和转归预测有重要作用。最后指出将来的研究需要将包括语义记忆成分在内的多种认知测验相结合,以便及早发现有可能发展为痴呆的危险个体并开展相应干预。     

孤独症个体的记忆与自我知识

本文从语义记忆-情景记忆角度综合了孤独症的记忆研究,探讨了孤独症个体的记忆特性。研究结果表明,孤独症个体的情景记忆(episodic memory)存在选择性损伤,特别是高机能孤独症个体的情景记忆测验的成绩会依材料的呈现方式和意义相关程度等表现出不同程度的损伤。同时,他们的语义记忆(semantic memory)相对完好,但和正常对照组语义记忆成绩之间的差异会随材料的性质而变化,这种差异并不显著。根据自我知识的存储方式以及孤独症的记忆特性,孤独症个体情景记忆中的自我知识丧失,语义记忆中所存储的自我知识则保存完好。孤独症个体虽然不能回忆与个人特质有关的个人行为,但是能回忆基于这些行为的关于自我的概括性知识。孤独症个体理解别人心理的能力严重受损,然而他们反映自己心理特性和状态的能力保持完好。     

自我相关未来思考:两种基本类型及其主要心理成分比较

自我相关未来思考是个体产生自我相关未来想法的心理加工,它包括未来情景思考和未来个人语义思考两种基本类型。两类思考都需记忆、自我和主观时间三种主要心理成分参与,但参与的具体形式可能有所不同:未来情景思考可能主要依赖于情景记忆和语义记忆、情景自我知识和语义自我知识、经验时间;未来个人语义思考可能主要依赖于语义记忆、语义自我知识和知道时间。三种主要心理成分在两种思考类型中的作用可能是相同的,其中,记忆是原材料,自我起引导作用,主观时间是先决条件。将来可以参照思考未来公众抽象问题的研究进一步明确自我和记忆在未来个人语义思考中的作用,还可以通过探究不同心理成分内部及成分间的交互作用进而了解各成分在自我相关未来思考中的作用机制。     

范畴特异性损伤与人脑中一般知识的组织

1 引言 记忆是多层面的。根据记忆中所存储的材料的性质,人类记忆可分为情节记忆和语义记忆。其中,语义记忆是指被组织起来的、关于世界的一般知识。人脑中一般知识如何组织,是当前认知神经科学争论的热点问题之一。脑损伤病人身上所观察到的语义记忆损伤模式,为回答这一问题提供了难得的机会。     

音高和时长信息感知的范畴特异性及其发展

通过考察不同范畴间相同声音特征和同一范畴内不同声音特征的感知探讨了言语和音乐中音高和时长信息感知的特异性及发展模式。结果发现：同一范畴内不同声音特征的感知显著相关,支持音高和时长信息加工的范畴特异性理论;高一学生只在言语中的音高和时长信息的感知上具有明显的范畴特异性,说明范畴特异性的形成因声音范畴属性的不同而有所差异;高一学生言语中音高信息的感知能力好于对时长信息的感知,而成人却没有差异,可能是受到了母语和第二语言学习经验的影响。     

基于名人面孔视觉特征和语义信息的视觉统计学习

视觉统计学习是指个体依据视觉刺激之间的转接概率来掌握统计规律的过程。本研究通过5个实验探讨了个体基于名人面孔视觉特征和语义信息进行视觉统计学习的加工机制。每个实验均包括熟悉(学习)和测试两个阶段：在熟悉阶段, 让被试观看名人面孔并完成重复图片探测的无关任务; 在测试阶段, 让被试进行二选一迫选任务。其中, 实验1和2分别考察基于名人面孔视觉特征和语义信息的视觉统计学习效果; 实验3分别考察基于名人面孔视觉特征和语义信息视觉进行统计学习的精确性; 实验4进一步考察基于名人面孔视觉特征和语义信息进行视觉统计学习的时间特征; 实验5验证基于名人面孔视觉特征的视觉统计学习具有面孔特异性。结果表明：个体能同时基于名人面孔视觉特征和语义信息进行精确的视觉统计学习; 基于正立名人面孔的视觉统计学习效果显著高于基于倒置名人面孔的视觉统计学习效果; 虽然基于视觉特征和语义信息的统计加工都具有一致的精确性, 但后者需要更多的加工时间。这提示：基于名人面孔视觉特征的视觉统计学习具有面孔特异性, 个体基于名人面孔视觉特征和语义信息的视觉统计学习过程是分离的, 统计运算发生于面孔特征加工完成之后。     

命题网络模型和ACT理论

ACT理论是G.Anderson 1976年提出的一种语义记忆理论。在ACT理论里,Anderson将知识划分为陈述性知识和程序性知识。陈述性知识用命题网络表征,程序性知识由产生式系统组成。每种知识的运用都遵循一系列假定。ACT理论的合理性已初步为实验证实。和其它语义记忆的理论相比,ACT具有(1)符合长时记忆的一般特征和(2)能解释分类语义记忆发现的优点。这种理论对于我们理解人类的记忆组织、知识表征、人类怎样理解语言、怎样推理和解决问题是有帮助的。     

记住过去与知道过去

加拿大心理学家E.Tulving提出长时记忆可以区分为事件记忆和语义记忆两个独立而又互有关联的系统,并从记忆检索角度对此作了说明。他提出,记忆过去(事件检索)和知道过去(语义检索)是不同的,事件记忆检索的是个体的,时间上确定的,并且与自我有关的事实,而语义记忆检索的是非个体的,时间上不确定的,与世界有关的事实。E.Tulving还用一名脑损伤导致健忘症的个案和大脑皮层血流模式在两种检索时的变化来证明他的理论是有根据的。最后,E.Tulving提出应用多种记忆系统的理论来取代传统的记忆统一性思想。     

Deregulated semantic cognition contributes to object‐use deficits in Alzheimer's disease: A comparison with semantic aphasia and semantic dementia

Executive control is impaired from the early stages of Alzheimer's Disease (AD) and this produces deregulated semantic cognition (Corbett, Jefferies, Burns, & Lambon Ralph, 2012 ; Perry, Watson, & Hodges, 2000 ). While control deficits should affect semantic retrieval across all modalities, previous studies have typically focused on verbal semantic tasks. Even when non‐verbal semantic tasks have been used, these have typically employed simple picture‐matching tasks, which may be influenced by abnormalities in covert naming. Therefore, in the present study, we examined 10 patients with AD on a battery of object‐use tasks, in order to advance our understanding of the origins of non‐verbal semantic deficits in this population. The AD patients’ deficits were contrasted with previously published performance on the same tasks within two additional groups of patients, displaying either semantic degradation (semantic dementia) or deregulation of semantic retrieval (semantic aphasia; Corbett, Jefferies, Ehsan, & Lambon Ralph, 2009 ). While overall accuracy was comparable to the scores in both other groups, the AD patients’ object‐use impairment most closely resembled that observed in SA; they exhibited poorer performance on comprehension tasks that placed strong demands on executive control. A similar pattern was observed in the expressive domain: the AD and SA groups were relatively good at straightforward object use compared to executively demanding, mechanical puzzles. Error types also differed: while all patients omitted essential actions, the SA and AD groups’ demonstrations also featured unrelated intrusions. An association between AD patients’ object use and their scores on standard executive measures suggested that control deficits contributed to their non‐verbal semantic deficits. Moreover, in a task specifically designed to manipulate executive demand, patients with AD (and SA) exhibited difficulty in thinking flexibly about the non‐canonical uses of everyday objects, especially when distracted by semantically related objects. This study provides converging evidence for the notion that a failure of regulatory control contributes to multimodal semantic impairment in AD and uniquely demonstrates this pattern for the highly non‐verbal domain of object use.     

To what extent does typicality boost semantic priming effects between members of their categories?

Atypical items of their semantic category yield more generalisation than their typical members when relearning in connectionist networks (Plaut, D. C. (1996). Relearning after damage in connectionist networks: toward a theory of rehabilitation. Brain and Language, 52(1), 25–82) and in empirical studies (Kiran, S., & Thompson, C. K. (2003). The role of semantic complexity in treatment of naming deficits: Training semantic categories in fluent aphasia by controlling exemplar typicality. Journal of Speech, Language, and Hearing Research, 46(4), 773–787). It seems therefore that atypical words provide more information about the overall structure of the semantic category due to their specific and shared features. In this view, atypical primes could strongly facilitate the processing of targets compared to typical primes, because typical primes contain little information about the variation between members within a category. In contrast, three semantic priming experiments in visual word recognition showed an advantage with the typical context, but not with the atypical one. These findings were observed in a variety of tasks, including lexical decision, categorisation and semantic judgment. Our results do not support the findings about generalisation in relearning and suggest that typicality effects in semantic priming mostly come from the activation of representative features of categories.     

Divergent effects of healthy ageing on semantic knowledge and control: Evidence from novel comparisons with semantically impaired patients

Effective use of semantic knowledge requires a set of conceptual representations and control processes which ensure that currently relevant aspects of this knowledge are retrieved and selected. It is well-established that levels of semantic knowledge increase across the lifespan. However, the effects of ageing on semantic control processes have not been assessed. I addressed this issue by comparing the performance profiles of young and older people on a verbal comprehension test. Two sets of variables were used to predict accuracy and RT in each group: (1) the psycholinguistic properties of words probed in each trial and (2) the performance on each trial by two groups of semantically impaired neuropsychological patients. Young people demonstrated poor performance for low-frequency and abstract words, suggesting that they had difficulty processing words with intrinsically weak semantic representations. Indeed, performance in this group was strongly predicted by the performance of patients with semantic dementia, who suffer from degradation of semantic knowledge. In contrast, older adults performed poorly on trials where the target semantic relationship was weak and distractor relationships strong – conditions which require high levels of controlled processing. Their performance was not predicted by the performance of semantic dementia patients, but was predicted by the performance of patients with semantic control deficits. These findings indicate that the effects of ageing on semantic cognition are more complex than has previously been assumed. While older people have larger stores of knowledge than young people, they appear to be less skilled at exercising control over the activation of this knowledge.     

The organization of conceptual knowledge: the evidence from category-specific semantic deficits

Questions about the organization of conceptual knowledge in the human brain can be addressed by studying patients with category-specific semantic deficits: disproportionate and even selective impairment of conceptual knowledge of one category of objects compared with other categories. Recently, consensus has emerged regarding the basic facts of category-specific semantic deficits: (1) the categories that can be disproportionately impaired or spared are 'animals', 'fruit/vegetables', and 'artifacts'; and (2) category-specific semantic deficits are not associated with disproportionate deficits for a type or modality of knowledge. Together with findings in functional neuroimaging, these data indicate a complex organization of conceptual knowledge characterized by several independent dimensions of organization.     

Category size effects in semantic and letter fluency in Alzheimer's patients

Many studies have found that patients with Alzheimer's disease (AD) perform significantly worse than normal controls on verbal fluency tasks. Moreover, some studies have found that AD patients' deficits compared to controls are more severe for semantic fluency (e.g., vegetables) than for letter fluency (e.g. words that begin with F). These studies, however, have not taken category size into account. A comparison of AD patients and age-matched controls on three semantic and three letter categories revealed that both the size and type of a category significantly predicted AD patients' deficits on verbal fluency tasks. These results suggest that the verbal fluency of AD patients will be most attenuated on large semantic categories.     

Impaired semantic memory during acute transient global amnesia

As a clinical model of hippocampal dysfunction, transient global amnesia (TGA) causes reversible memory disturbance. While episodic memory deficits in TGA patients have been extensively described, data regarding semantic memory involvement are sparse and contradictory. We report impaired semantic fluency performance in 16 patients with hippocampal lesions on MRI during acute TGA compared to their performance one day later and to that of 20 healthy subjects. Our findings support the involvement of the hippocampus in semantic retrieval.     

The contribution of executive control to semantic cognition: Convergent evidence from semantic aphasia and executive dysfunction

Semantic cognition, as described by the controlled semantic cognition (CSC) framework (Rogers et al., 2015 , Neuropsychologia, 76, 220), involves two key components: activation of coherent, generalizable concepts within a heteromodal ‘hub’ in combination with modality‐specific features (spokes), and a constraining mechanism that manipulates and gates this knowledge to generate time‐ and task‐appropriate behaviour. Executive–semantic goal representations, largely supported by executive regions such as frontal and parietal cortex, are thought to allow the generation of non‐dominant aspects of knowledge when these are appropriate for the task or context. Semantic aphasia (SA) patients have executive–semantic deficits, and these are correlated with general executive impairment. If the CSC proposal is correct, patients with executive impairment should not only exhibit impaired semantic cognition, but should also show characteristics that align with those observed in SA. This possibility remains largely untested, as patients selected on the basis that they show executive impairment (i.e., with ‘dysexecutive syndrome’) have not been extensively tested on tasks tapping semantic control and have not been previously compared with SA cases. We explored conceptual processing in 12 patients showing symptoms consistent with dysexecutive syndrome (DYS) and 24 SA patients, using a range of multimodal semantic assessments which manipulated control demands. Patients with executive impairments, despite not being selected to show semantic impairments, nevertheless showed parallel patterns to SA cases. They showed strong effects of distractor strength, cues and miscues, and probe–target distance, plus minimal effects of word frequency on comprehension (unlike semantic dementia patients with degradation of conceptual knowledge). This supports a component process account of semantic cognition in which retrieval is shaped by control processes, and confirms that deficits in SA patients reflect difficulty controlling semantic retrieval.     

The update of semantic memories in amnestic mild cognitive impairment

It is still controversial to what extent neocortical consolidated memories are susceptible of change by processes of reconsolidation and transformation throughout experience, and whether the medial temporal lobes are necessary for this update of semantic consolidated memories, as they are for episodic remembering. We hypothesize that patients with amnestic mild cognitive impairment (aMCI) who have deficits in episodic memory may also have difficulties in updating information on added new features of objects. Sixteen participants with aMCI and 20 healthy control participants performed a semantic word-to-picture task, in which they were asked to identify as belonging to a given semantic category NEW objects, that have incorporated novel features, as well as OLD items, semantically and visually SIMILAR items and UNRELATED items. Patients with aMCI made a greater percentage of errors than healthy controls. Participants globally made greater percentages of errors in difficult types of items, namely NEW and SIMILAR, as compared to easier ones, OLD and UNRELATED. Importantly, an item by diagnostic group interaction effect was observed, and post hoc analysis showed that patients with aMCI made a higher percentage of errors than controls in NEW items only. In conclusion, patients with aMCI had a particular difficulty in identifying the NEW items of the word-to-picture task as compared to the control participants, supporting the concept of a flexible and dynamic conceptual knowledge system, involving the update of semantic memories and the integration of new attributes in a constant transformation process, which is impaired in these patients.