A progressive category-specific semantic deficit for non-living things

Semantic feature production norms for manipulable objects

Feature generation tasks and feature databases are important for understanding how knowledge is organized in semantic memory, as they reflect not only the kinds of information that individuals hold about objects but also how objects are conceptually represented. Traditionally, semantic norms focus on a variety of object categories and, as a result, have a small number of concepts per semantic category. Here, our main goal is to create a more fine-grained feature database exclusively for one category of objects-manipulable objects. This database contributes to the understanding of within-category, content-specific processing. To achieve this, we asked 130 participants to freely generate features for 80 manipulable objects and another group of 32 participants to generate action features for the same objects. We then compared our databases with other published semantic norms and found high similarity between them. In our databases, we calculated the similarity between objects in terms of visual, functional, encyclopaedic, and action feature types using Spearman correlation, Baker's gamma index, and cophenetic correlation. We discovered that objects were grouped in a distinctive and meaningful way according to feature type. Finally, we tested the validity of our databases by asking three groups of participants to perform a feature verification experiment while manipulating production frequency. Our results demonstrate that participants can recognize and associate the features of our databases with specific manipulable objects. Participants were faster to verify high-frequency features than low-frequency features. Overall, our data provide important insights into how we process manipulable objects and can be used to further inform cognitive and neural theories of object processing and identification.

RealPic: Picture norms of real-world common items

Pictures are often used as stimuli in several fields, such as psychology and neuroscience. However, co-occurring image-related properties might impact their processing, emphasizing the importance of validating such materials to guarantee the quality of research and professional practices. This is particularly relevant for pictures of common items because of their wide applicability potential. Normative studies have already been conducted to create and validate such pictures, yet most of them focused on stimulus without naturalistic elements (e.g., line drawings). Norms for real-world pictures of common items are rare, and their normative examination does not always simultaneously assess affective, semantic and perceptive dimensions, namely in the Portuguese context. Real-world pictures constitute pictorial representations of the world with realistic details (e.g., natural color or position), thus improving their ecological validity and their suitability for empirical studies or intervention purposes. Consequently, the establishment of norms for real-world pictures is mandatory for exploring their ecological richness and to uncover their impact across several relevant dimensions. In this study, we established norms for 596 real-world pictures of common items (e.g., tomato, drum) selected from existing databases and distributed into 12 categories. The pictures were evaluated on nine dimensions by a Portuguese sample. The results present the norms by item, by dimension and their correlations as well as cross-cultural analyses. RealPic is a culturally based dataset that offers systematic and flexible standards and is suitable for selecting stimuli while controlling for confounding effects in empirical tasks and interventional applications.

A Systematic Review of Normative Studies Using Images of Common Objects

Common objects comprise living and non-living things people interact with in their daily-lives. Images depicting common objects are extensively used in different fields of research and intervention, such as linguistics, psychology, and education. Nevertheless, their adequate use requires the consideration of several factors (e.g., item-differences, cultural-context and confounding correlated variables), and careful validation procedures. The current study presents a systematic review of the available published norms for images of common objects. A systematic search using PRISMA guidelines indicated that despite their extensive use, the production of norms for such stimuli with adult populations is quite limited (N = 55), particularly for more ecological images, such as photos (N = 14). Among the several dimensions in which the items were assessed, the most commonly referred in our sample were familiarity, visual complexity and name agreement, illustrating some consistency across the reported dimensions while also indicating the limited examination of other potentially relevant dimensions for image processing. The lack of normative studies simultaneously examining affective, perceptive and semantic dimensions was also documented. The number of such normative studies has been increasing in the last years and published in relevant peer-reviewed journals. Moreover, their datasets and norms have been complying with current open science practices. Nevertheless, they are still scarcely cited and replicated in different linguistic and cultural contexts. The current study brings important theoretical contributions by characterizing images of common objects stimuli and their culturally-based norms while highlighting several important features that are likely to be relevant for future stimuli selection and evaluative procedures. The systematic scrutiny of these normative studies is likely to stimulate the production of new, robust and contextually-relevant normative datasets and to provide tools for enhancing the quality of future research and intervention.

Multimodal semantic battery to monitor progressive loss of concepts in the semantic variant of primary progressive aphasia (svPPA): an innovative proposal

Semantic variant primary progressive aphasia (svPPA) is a rare neurodegenerative disease characterized by a progressive loss of semantic knowledge. Patients with svPPA show anomia, impaired word comprehension, poor object recognition, and difficulties in retrieving semantic information. svPPA is also a unique "natural" model that allows clinicians and cognitive neuroscientists to study the organization of semantic memory because only semantic knowledge is affected in the initial period of the disease, with relative sparing of other cognitive domains. In the clinical practice, semantic memory is commonly tested only with verbal tests. The aim of the present study was to preliminary test a new Multimodal Semantic Battery developed in our laboratory, which comprised 11 subtests designed to assess the semantic knowledge of multiple items via all input modalities. The battery was administered twice, over four years, to a patient diagnosed with svPPA. We found that when extensively tested with multiple tests, in some cases, he was still able to recall semantic features of the items that otherwise would not have emerged with standard semantic tests. These results are discussed for the clinical practice: monitoring semantic memory through all modalities in a practical and reliable way could be useful for both clinicians and experimental researchers to better investigate the breakdown of semantic knowledge.

A feature-based neurocomputational model of semantic memory

According with a featural organization of semantic memory, this work is aimed at investigating, through an attractor network, the role of different kinds of features in the representation of concepts, both in normal and neurodegenerative conditions. We implemented new synaptic learning rules in order to take into account the role of partially shared features and of distinctive features with different saliency. The model includes semantic and lexical layers, coding, respectively for object features and word-forms. Connections among nodes are strongly asymmetrical. To account for the feature saliency, asymmetrical synapses were created using Hebbian rules of potentiation and depotentiation, setting different pre-synaptic and post-synaptic thresholds. A variable post-synaptic threshold, which automatically changed to reflect the feature frequency in different concepts (i.e., how many concepts share a feature), was used to account for partially shared features. The trained network solved naming tasks and word recognition tasks very well, exploiting the different role of salient versus marginal features in concept identification. In the case of damage, superordinate concepts were preserved better than the subordinate ones. Interestingly, the degradation of salient features, but not of marginal ones, prevented object identification. The model suggests that Hebbian rules, with adjustable post-synaptic thresholds, can provide a reliable semantic representation of objects exploiting the statistics of input features.

Distinctive semantic features in the healthy adult brain

The role of semantic features, which are distinctive (e.g., a zebra's stripes) or shared (e.g. has four legs) for accessing a concept, has been studied in detail in early neurodegenerative disease such as semantic dementia (SD). However, potential neural underpinnings of such processing have not been studied in healthy adults. The current study examines neural activation patterns using fMRI while participants completed a feature verification task, in which they identified shared or distinctive semantic features for a set of natural kinds and man-made artifacts. The results showed that the anterior temporal lobe bilaterally is an important area for processing distinctive features, and that this effect is stronger within natural kinds than man-made artifacts. These findings provide converging evidence from healthy adults that is consistent with SD research, and support a model of semantic memory in which patterns of specificity of semantic information can partially explain differences in neural activation between categories.

Linguistic Aspects of Primary Progressive Aphasia

Primary progressive aphasia (PPA) refers to a disorder of declining language associated with neurodegenerative diseases such as frontotemporal degeneration and Alzheimer disease. Variants of PPA are important to recognize from a medical perspective because these syndromes are clinical markers suggesting specific underlying pathology. In this review, I discuss linguistic aspects of PPA syndromes that may prove informative for parsing our language mechanism and identifying the neural representation of fundamental elements of language. I focus on the representation of word meaning in a discussion of semantic variant PPA, grammatical comprehension and expression in a discussion of nonfluent/agrammatic variant PPA, the supporting role of short-term memory in a discussion of logopenic variant PPA, and components of language associated with discourse in a discussion of behavioral variant frontotemporal dementia. PPA provides a novel perspective that uniquely addresses facets of language and its disorders while complementing traditional aphasia syndromes that follow stroke.

Abnormal semantic knowledge in a case of developmental amnesia

An important theory holds that semantic knowledge can develop independently of episodic memory. One strong source of evidence supporting this independence comes from the observation that individuals with early hippocampal damage leading to developmental amnesia generally perform normally on standard tests of semantic memory, despite their profound impairment in episodic memory. However, one aspect of semantic memory that has not been explored is conceptual structure. We built on the theoretically important distinction between intrinsic features of object concepts (e.g., shape, colour, parts) and extrinsic features (e.g., how something is used, where it is typically located). The accrual of extrinsic feature knowledge that is important for concepts such as chair or spoon may depend on binding mechanisms in the hippocampus. We tested HC, an individual with developmental amnesia due to a well-characterized lesion of the hippocampus, on her ability to generate semantic features for object concepts. HC generated fewer extrinsic features than controls, but a similar number of intrinsic features than controls. We also tested her on typicality ratings. Her typicality ratings were abnormal for nonliving things (which more strongly depend on extrinsic features), but normal for living things (which more strongly depend on intrinsic features). In contrast, NB, who has MTL but not hippocampal damage due to surgery, showed no impairments in either task. These results suggest that episodic and semantic memory are not entirely independent, and that the hippocampus is important for learning some aspects of conceptual knowledge.

A fast and implicit measure of semantic categorisation using steady state visual evoked potentials

There is a great need for objective measures of perception and cognition that are reliable at the level of the individual subject. Although traditional electroencephalography (EEG) techniques can act as valid bio-markers of cognition, they typically involve long recording times and the computation of group averages. To overcome these well-known limitations of EEG, vision scientists have recently introduced a steady state method known as fast periodic visual stimulation (FPVS). This method allows them to study visual discrimination at the individual level. Inspired by their work, we examined whether FPVS could be used equally effectively to capture abstract conceptual processes. Twenty subjects (20.9 (±2.1) yrs, 6 male) were asked to complete a FPVS-oddball paradigm that assessed their spontaneous ability to differentiate between rapidly presented images on the basis of semantic, rather than perceptual, properties. At the group level, this approach returned a reliable oddball detection response after only 50s of stimulus presentation time. Moreover, a stable oddball response was found for each participating individual within 100s. As such, the FPVS-oddball paradigm returned an objective, non-verbal marker of semantic categorisation in single subjects in under two minutes. This finding establishes the FPVS-oddball paradigm as a powerful new tool in cognitive neuroscience.

Semantic Knowledge Use in Discourse: Influence of Age

Semantic memory is relatively stable across the lifespan (Rönnlund, Nyberg, & Bäckman, 2005; Spaniol, Madden, & Voss, 2006); however, most research has been conducted at the single concept level. Few researchers have examined how semantic knowledge is used in discourse. The purpose of the study, then, was to determine the proportion of semantic knowledge and category domains used in discourse produced by younger and older participants. Cognitively healthy, younger (n=30, 20-39) and older (n=30; 60-89) participants told stories that were transcribed and coded for 10 domains of semantic knowledge and also living and nonliving things. Results indicated group differences for the proportion of semantic knowledge type, sound, and for the category type, living things. These findings extend previous research on semantic features into the realm of discourse and indicate the importance of studying semantic features and categories within discourse.

Past, present, and prospects: Reflections 40 years on from the selective impairment of semantic memory (Warrington, 1975)

We summarize the main findings and conclusions of Warrington's (1975) paper, The Selective Impairment of Semantic memory, a neuropsychological paper that described three cases with degenerative neurological conditions [Warrington, E. K. (1975). The selective impairment of semantic memory. The Quarterly Journal of Experimental Psychology, 27, 635–657]. We consider the developments that have followed from its publication and give a selective overview of the field in 2014. The initial impact of the paper was on neuropsychological investigations of semantic loss followed some 14 years later by the identification of Semantic Dementia (the condition shown by the original cases) as a distinctive form of degenerative disease with unique clinical and pathological characteristics. We discuss the distinction between disorders of semantic storage and refractory semantic access, the evidence for category- and modality-specific impairments of semantics, and the light that has been shed on the structure and organization of semantic memory. Finally we consider the relationship between semantic memory and the skills of reading and writing, phonological processing, and autobiographical memory.

Semantic Knowledge Use in Discourse Produced by Individuals with Anomic Aphasia

BACKGROUND

Researchers have demonstrated that people with aphasia (PWA) have preserved semantic knowledge (Dell et al., 1997; Jefferies & Lambon Ralph, 2006). However, Antonucci (2014) demonstrated that some PWA have impaired access to certain types of knowledge more than others. Yet, all these studies used single concepts. It has not been demonstrated whether PWA have difficulty accessing certain types of features within a discourse sample.

AIMS

The main goals of this study were to determine if semantic knowledge and two category types were used differently within discourse produced by participants with anomic aphasia and healthy controls.

METHOD & PROCEDURES

Participants with anomic aphasia (n=19) and healthy controls (n=19) told stories that were transcribed and coded for 10 types of semantic knowledge and two category types, living and nonliving things.

OUTCOMES & RESULTS

A Poisson regression model was conducted. The results indicated a significant difference between the groups for the semantic knowledge types, sound and internal state, but no difference was found for category types. Yet the distribution of semantic knowledge and category types produced within the discourse samples were similar between the groups.

CONCLUSION

PWA might have differential access to certain types of semantic knowledge within discourse production, but it does not rise to the level of categorical deficits. These findings extend single-concept research into the realm of discourse.

Revisiting domain-general accounts of category specificity in mind and brain

Theories about the neural basis of semantic knowledge have been strongly influenced by reports that particular semantic categories can be differentially impaired by neuropathology and can differentially activate particular regions of cortex in brain imaging studies. One well-known interpretation of these data is that the brain has evolved distinct functional and anatomical modules for storing and retrieving knowledge about different kinds of things. We review the evidence supporting an alternative view: that category specificity arises from many heterogeneous factors and so tells us little directly about the cognitive and neural architecture of semantic memory. We consider four general hypotheses about domain-general causes of category-specific patterns, their roots in early work, and their reemergence in contemporary research. We argue that there is compelling evidence supporting each hypothesis, and that the different hypotheses together can explain most of the interesting data. We further suggest that such a multifactor domain-general approach to category specificity is appealing partly because it explains the important findings with reference to theoretical claims that are already widely accepted, and partly because it resolves several puzzles that arise under the alternative view. For further resources related to this article, please visit the WIREs website.

CONFLICT OF INTEREST

The authors have declared no conflicts of interest for this article.

Comparative semantic profiles in semantic dementia and Alzheimer's disease

Patients with the semantic variant of primary progressive aphasia, also known as semantic dementia, and Alzheimer's disease have deficits in semantic memory. However, few comparative studies have been performed to determine whether these patient groups have distinct semantic memory impairments. We asked 15 patients with semantic variant primary progressive aphasia and 57 patients with Alzheimer's disease to judge semantic category membership of coloured photos and printed words that are members of familiar natural and manufactured categories, and we related performance to grey matter atrophy. We found that both semantic variant primary progressive aphasia and Alzheimer's disease are significantly impaired on this task. Moreover, patients with semantic variant primary progressive aphasia had a significantly more prominent deficit for natural objects than their own deficit judging manufactured objects. Both semantic variant primary progressive aphasia and Alzheimer's disease had atrophy that included portions of the left temporal lobe. Regression analyses related performance in semantic variant primary progressive aphasia to ventral and medial portions of the left temporal lobe, while regression analyses in Alzheimer's disease related performance to these ventral and medial temporal areas as well as lateral temporal-parietal regions in the left hemisphere. We conclude that both semantic variant primary progressive aphasia and Alzheimer's disease are significantly impaired in a simple category membership judgement task and the selective impairment for natural kinds in semantic variant primary progressive aphasia is related in part to disease in visual association cortex in ventral-medial portions of the left temporal lobe. We discuss factors that may contribute to the semantic memory deficit in semantic variant primary progressive aphasia.

Ultra rapid object categorization: effects of level, animacy and context

It is widely agreed that in object categorization bottom-up and top-down influences interact. How top-down processes affect categorization has been primarily investigated in isolation, with only one higher level process at a time being manipulated. Here, we investigate the combination of different top-down influences (by varying the level of category, the animacy and the background of the object) and their effect on rapid object categorization. Subjects participated in a two-alternative forced choice rapid categorization task, while we measured accuracy and reaction times. Subjects had to categorize objects on the superordinate, basic or subordinate level. Objects belonged to the category animal or vehicle and each object was presented on a gray, congruent (upright) or incongruent (inverted) background. The results show that each top-down manipulation impacts object categorization and that they interact strongly. The best categorization was achieved on the superordinate level, providing no advantage for basic level in rapid categorization. Categorization between vehicles was faster than between animals on the basic level and vice versa on the subordinate level. Objects in homogenous gray background (context) yielded better overall performance than objects embedded in complex scenes, an effect most prominent on the subordinate level. An inverted background had no negative effect on object categorization compared to upright scenes. These results show how different top-down manipulations, such as category level, category type and background information, are related. We discuss the implications of top-down interactions on the interpretation of categorization results.

Semantic knowledge fractionations: verbal propositions vs. perceptual input? Evidence from a child with Klinefelter syndrome

This paper addresses the relative independence of different types of lexical- and factually-based semantic knowledge in JM, a 9-year-old boy with Klinefelter syndrome (KS). JM was matched to typically developing (TD) controls on the basis of chronological age. Lexical-semantic knowledge was investigated for common noun (CN) and mathematical vocabulary items (MV). Factually-based semantic knowledge was investigated for general and number facts. For CN items, JM's lexical stores were of a normal size but the volume of correct 'sensory feature' semantic knowledge he generated within verbal item descriptions was significantly reduced. He was also significantly impaired at naming item descriptions and pictures, particularly for fruit and vegetables. There was also weak object decision for fruit and vegetables. In contrast, for MV items, JM's lexical stores were elevated, with no significant difference in the amount and type of correct semantic knowledge generated within verbal item descriptions and normal naming. JM's fact retrieval accuracy was normal for all types of factual knowledge. JM's performance indicated a dissociation between the representation of CN and MV vocabulary items during development. JM's preserved semantic knowledge of facts in the face of impaired semantic knowledge of vocabulary also suggests that factually-based semantic knowledge representation is not dependent on normal lexical-semantic knowledge during development. These findings are discussed in relation to the emergence of distinct semantic knowledge representations during development, due to differing degrees of dependency upon the acquisition and representation of semantic knowledge from verbal propositions and perceptual input.

Medial perirhinal cortex disambiguates confusable objects

Our brain disambiguates the objects in our cluttered visual world seemingly effortlessly, enabling us to understand their significance and to act appropriately. The role of anteromedial temporal structures in this process, particularly the perirhinal cortex, is highly controversial. In some accounts, the perirhinal cortex is necessary for differentiating between perceptually and semantically confusable objects. Other models claim that the perirhinal cortex neither disambiguates perceptually confusable objects nor plays a unique role in semantic processing. One major hurdle to resolving this central debate is the fact that brain damage in human patients typically encompasses large portions of the anteromedial temporal lobe, such that the identification of individual substructures and precise neuroanatomical locus of the functional impairments has been difficult. We tested these competing accounts in patients with Alzheimer's disease with varying degrees of atrophy in anteromedial structures, including the perirhinal cortex. To assess the functional contribution of each anteromedial temporal region separately, we used a detailed region of interest approach. From each participant, we obtained magnetic resonance imaging scans and behavioural data from a picture naming task that contrasted naming performance with living and non-living things as a way of manipulating perceptual and semantic confusability; living things are more similar to one another than non-living things, which have more distinctive features. We manually traced neuroanatomical regions of interest on native-space cortical surface reconstructions to obtain mean thickness estimates for the lateral and medial perirhinal cortex and entorhinal cortex. Mean cortical thickness in each region of interest, and hippocampal volume, were submitted to regression analyses predicting naming performance. Importantly, atrophy of the medial perirhinal cortex, but not lateral perirhinal cortex, entorhinal cortex or hippocampus, significantly predicted naming performance on living relative to non-living things. These findings indicate that one specific anteromedial temporal lobe region-the medial perirhinal cortex-is necessary for the disambiguation of perceptually and semantically confusable objects. Taken together, these results support a hierarchical account of object processing, whereby the perirhinal cortex at the apex of the ventral object processing system is required to bind properties of not just perceptually, but also semantically confusable objects together, enabling their disambiguation from other similar objects and thus comprehension. Significantly, this model combining a hierarchical object processing architecture with a semantic feature statistic account explains why category-specific semantic impairments for living things are associated with anteromedial temporal lobe damage, and pinpoints the root of this syndrome to perirhinal cortex damage.

Do semantic categories activate distinct cortical regions? Evidence for a distributed neural semantic system

A key issue in cognitive neuroscience concerns the neural representation of conceptual knowledge. Currently, debate focuses around the issue of whether there are neural regions specialised for the processing of specific semantic attributes or categories, or whether concepts are represented in an undifferentiated neural system. Neuropsychological studies of patients with selective semantic deficits and previous neuroimaging studies do not unequivocally support either account. We carried out a PET study to determine whether there is any regional specialisation for the processing of concepts from different semantic categories using picture stimuli and a semantic categorisation task. We found robust activation of a large semantic network extending from left inferior frontal cortex into the inferior temporal lobe and including occipital cortex and the fusiform gyrus. The only category effect that we found was additional activation for animals in the right occipital cortex, which we interpret as being due to the extra visual processing demands required in order to differentiate one animal from another. We also carried out analyses in specific cortical regions that have been claimed to be preferentially activated for various categories, but found no evidence of any differential activation as a function of category. We interpret these data within the framework of cognitive accounts in which conceptual knowledge is represented within a nondifferentiated distributed system.

Dynamic processing in the human language system: synergy between the arcuate fascicle and extreme capsule

The production and comprehension of human language is thought to involve a network of frontal, parietal, and temporal cortical loci interconnected by two dominant white matter pathways. These two white matter bundles, often referred to as the dorsal and ventral processing tracts, are hypothesized to have markedly different language functions. The dorsal tract is thought to process phonological processing, while the ventral tract is considered to abet semantics. This proposed functional differentiation of tracts is similar to the ventral and dorsal dichotomy proposed for the visual and auditory systems. The present study evaluated this characterization of the language system in the context of various components involved in its function. Twenty-four chronic stroke patients completed a battery of 10 language tests designed to measure performance on the comprehension and production of phonology, morphology, semantics, and syntax. The patients also completed diffusion MRI scanning. Lesions were confined to the left hemisphere, but the size and location of the insult varied so that patients had damage to a single tract, both tracts, or neither tract. Individual FA maps were generated, and focal areas of hypointensity served as markers of white matter damage. Whole-brain voxel-by-voxel correlations revealed that only phonological and semantic tasks fit into the dual-stream model, while syntax and morphology involved both pathways. ROI analyses of the arcuate fascicle and extreme capsule supported this finding. These data suggest that natural language function is more likely to reflect a synergistic system rather than a segregated dual-stream system.

The question shapes the answer: the neural correlates of task differences reveal dynamic semantic processing

Task effects in semantic processing were investigated by contrasting the neural activation associated with two semantic categorization tasks (SCT) using event-related fMRI. The two SCTs involved different decision categories: is it an animal? vs. is it a concrete thing? Participants completed both tasks and, across participants, the same core set of items were presented in both tasks. Results showed task differences in the neural activation associated with these items: in the animal SCT there was greater activation in a number of frontal and temporal regions, including left superior and middle temporal gyri, while in the concrete SCT there was greater activation in left medial frontal gyrus and bilaterally in the precentral gyri. These results are interpreted as evidence of top-down modulation of semantic processing; participants make adjustments to optimize performance in a given task and these adjustments have consequences for the activation observed.

Interhemispheric differences in knowledge of animals among patients with semantic dementia

OBJECTIVE

To investigate interhemispheric differences on naming and fluency tasks for living versus nonliving things among patients with semantic dementia (SD).

BACKGROUND

In SD, left-temporal involvement impairs language and word comprehension, and right-temporal involvement impairs facial recognition. There may be other interhemispheric differences, particularly in the animate-inanimate dichotomy.

METHOD

On the basis of magnetic resonance imaging (MRI) ratings of anterior temporal atrophy, 36 patients who met criteria for SD were divided into 21 with left-predominant and 11 with right-predominant involvement (4 others were too symmetric for analysis). The left and right-predominant groups were compared on naming, fluency, and facial recognition tests.

RESULTS

Consistent with greater language impairment, the left-predominant patients had worse naming, especially inanimate and letter fluency, than the right-predominant patients. In contrast, difference in scores suggested selective impairment of animal naming, animal name fluency, and semantic knowledge for animate items among the right-predominant patients. Proportionally more right than left-predominant patients misnamed animal items and faces.

CONCLUSIONS

These findings support interhemispheric differences in animal knowledge. Whereas left-predominant SD equally affects animate and inanimate words from language involvement, right-predominant SD, with greater sparing of language, continues to impair other semantic aspects of animals. The right anterior temporal region seems to make a unique contribution to knowledge of living things.

Altered brain response for semantic knowledge in Alzheimer's disease

Word retrieval deficits are common in Alzheimer's disease (AD) and are thought to reflect a degradation of semantic memory. Yet, the nature of semantic deterioration in AD and the underlying neural correlates of these semantic memory changes remain largely unknown. We examined the semantic memory impairment in AD by investigating the neural correlates of category knowledge (e.g., living vs. nonliving) and featural processing (global vs. local visual information). During event-related fMRI, 10 adults diagnosed with mild AD and 22 cognitively normal (CN) older adults named aloud items from three categories for which processing of specific visual features has previously been dissociated from categorical features. Results showed widespread group differences in the categorical representation of semantic knowledge in several language-related brain areas. For example, the right inferior frontal gyrus showed selective brain response for nonliving items in the CN group but living items in the AD group. Additionally, the AD group showed increased brain response for word retrieval irrespective of category in Broca's homologue in the right hemisphere and rostral cingulate cortex bilaterally, which suggests greater recruitment of frontally mediated neural compensatory mechanisms in the face of semantic alteration.

Atypical semantic knowledge and autobiographical memory disorder in a young adult with Downs syndrome

A study of lexical semantic knowledge and autobiographical memory is described in PQ, a 22-year-old male with Downs syndrome. Performance is compared with younger typically developing verbal mental age controls. PQ's lexical stores contained a normal number of items, however, he was impaired at naming both pictures and item descriptions. PQ's own descriptions of items contained a normal volume of information, but the pattern of information differed from normal as he produced less 'sensory' and more 'thematic' and 'functional' information. PQ has an autobiographical memory deficit. His ability to recall 'specific' memories was significantly impoverished. It is suggested that both PQ's naming difficulties and his autobiographical memory disorder may reflect atypical knowledge specification with absence of distinctive featural knowledge and increased conceptual overlap and looser networks pervasive across both semantic and autobiographical memory systems.

Categorization of novel tools by patients with Alzheimer's disease: category-specific content and process

We examined the interaction of content and process in categorizing novel semantic material. We taught patients with Alzheimer's disease (AD) and healthy age-matched seniors a category of plausible novel tools by similarity- and rule-based processes, and compared the results with our previous parallel study of categorization of novel animals, in which AD patients were selectively impaired at rule-based categorization. AD patients demonstrated learning in the novel tool study; however, in contrast to the novel animal study, they were impaired in similarity-based as well as rule-based categorization relative to healthy seniors. Healthy seniors' categorization strategies reflected process irrespective of category content; they frequently attended to a single feature following similarity-based training, and always attended to all requisite features following rule-based training. AD patients' categorization strategies, in contrast, reflected category content; they frequently attended to a single feature when categorizing novel animals by either categorization process, but rarely did so when categorizing novel tools. AD patients' ability to categorize novel tools correlated with preserved recognition memory, a pattern not found in the novel animal study. The category-specific role of memory, along with AD patients' performance profile, suggests content-specific distinctions between the categories. We posit that tool features are relatively arbitrary, placing greater demands on memory, while prior knowledge about animals such as constraints on appearance and feature diagnosticity facilitates the assimilation of novel animals into semantic memory. The results suggest that categorization processes are sensitive to category content, which influences AD patients' success at acquiring a new category.

A unitary account of conceptual representations of animate/inanimate categories

In this paper we present an ERP study examining the underlying nature of semantic representation of animate and inanimate objects. Time-locking ERP signatures to the onset of auditory stimuli we found topological similarities in animate and inanimate object processing. Moreover, we found no difference between animates and inanimates in the N400 amplitude, when mapping more specific to more general representation (visual to auditory stimuli). These studies provide further evidence for the theory of unitary semantic organization, but no support for the feature-based prediction of segregated conceptual organization. Further comparisons of animate vs. inanimate matches and within-vs. between-category mismatches revealed following results: processing of animate matches elicited more positivity than processing of inanimates within the N400 time-window; also, inanimate mismatches elicited a stronger N400 than did animate mismatches. Based on these findings we argue that one of the possible explanations for finding different and sometimes contradictory results in the literature regarding processing and representations of animates and inanimates in the brain could lie in the variability of selected items within each of the categories, that is, homogeneity of the categories.

Shared and/or separate representations of animate/inanimate categories: An ERP study

This paper presents an ERP experiment examining the underlying nature of semantic representation of animate and inanimate objects. Time-locking ERP signatures to the onset of visual stimuli we found topological similarities in animate and inanimate object processing. Moreover, when mapping more general to more specific representation (auditory to visual stimuli) we found no difference between animates and in animates in the N400 amplitude either. This study provides further evidence for the theory of unitary semantic organization, but no support for the feature-based prediction of segregated conceptual organization. Surprisingly, it was also found that the P600 component, which has been thus far mostly related to syntactic processing to be a sensitive index of conceptual processing. The most apparent difference regarding P600 component was found between animate and inanimate matches, whereby animate matches elicited more positive ERP signatures in comparison to inanimate matches.

Longitudinal studies of semantic dementia: the relationship between structural and functional changes over time

The pattern of brain atrophy in semantic dementia and its associated cognitive effects have attracted a considerable body of research, but the nature of core impairments remains disputed. A key issue is whether the disease encompasses one neurocognitive network (semantics) or two (language and semantics). In order to address these conflicting perspectives, we conducted a longitudinal investigation of two semantic dementia patients, in which behavioural performance across a range of measures of language and semantic performance was assessed and interpreted in the context of annually acquired MRI scans. Our results indicated a core semantic impairment in early stages of the disease, associated with atrophy of the inferior, anterior temporal cortex. Linguistic impairments emerged later, and were contingent on atrophy having spread into areas widely believed to subserve core language processes (left posterior perisylvian, inferior frontal and insular cortex). We claim, therefore, that phonological, syntactic and morphological processing deficits in semantic dementia reflect damage to core language areas. Further, we propose that much of the current controversy over the nature of deficits in semantic dementia reflect a tendency in the literature to adopt a static perspective on what is a progressive disease. An approach in which the relationship between progressive neural changes and behavioural change over time is carefully mapped, offers a more constraining data-set from which to draw inferences about the relationship between language, semantics and the brain.

Functional Representation of Living and Nonliving Domains across the Cerebral Hemispheres: A Combined Event-related Potential/Transcranial Magnetic Stimulation Study

Transcranial magnetic stimulation (TMS) over the left hemisphere has been shown to disrupt semantic processing but, to date, there has been no direct demonstration of the electrophysiological correlates of this interference. To gain insight into the neural basis of semantic systems, and in particular, study the temporal and functional organization of object categorization processing, we combined repetitive TMS (rTMS) and ERPs. Healthy volunteers performed a picture–word matching task in which Snodgrass drawings of natural (e.g., animal) and artifactual (e.g., tool) categories were associated with a word. When short trains of high-frequency rTMS were applied over Wernicke's area (in the region of the CP5 electrode) immediately before the stimulus onset, we observed delayed response times to artifactual items, and thus, an increased dissociation between natural and artifactual domains. This behavioral effect had a direct ERP correlate. In the response period, the stimuli from the natural domain elicited a significant larger late positivity complex than those from the artifactual domain. These differences were significant over the centro-parietal region of the right hemisphere. These findings demonstrate that rTMS interferes with postperceptual categorization processing of natural and artifactual stimuli that involve separate subsystems in distinct cortical areas.

Deafness for the meanings of number words

We describe the performance of an aphasic individual who showed a selective impairment affecting his comprehension of auditorily presented number words and not other word categories. His difficulty in number word comprehension was restricted to the auditory modality, given that with visual stimuli (written words, Arabic numerals and pictures) his comprehension of number and non-number words was intact. While there have been previous reports of selective difficulty or sparing of number words at the semantic and post-semantic levels, this is the first reported case of a pre-semantic deficit that is specific to the category of number words. This constitutes evidence that lexical semantic distinctions are respected by modality-specific neural mechanisms responsible for providing access to the meanings of words.

Category-specific semantic deficits in Alzheimer's disease: a semantic priming study

Category-specific semantic deficits in individuals suffering brain damage after relatively focal lesions provide an important source of evidence about the organization of semantic knowledge. However, whether Alzheimer's disease (AD), in which the brain damage is more widespread, affects semantic categories to a different extent is still controversial. In the present study, we assess this issue by means of the semantic priming technique. AD patients with a mild impairment of their semantic knowledge showed comparable priming effects to that of controls for the categories of animals and artifacts. Interestingly, however, patients with a moderate impairment of their semantic knowledge showed a normal priming effect for animals but a very reduced priming effect (if any) for artifacts. These results reveal that AD may affect the semantic knowledge of different semantic categories to a different extent. The implications of this observation for current theoretical accounts of semantic representation in the brain are discussed.

Neuropsychological and psychiatric profiles in acute encephalitis in adults

Acute encephalitis is an inflammation of brain tissue that can result from activity in the central nervous system (CNS) of a number of viruses. Although the neurological and psychiatric effects of encephalitis in the acute phase of the illness are well-known (Caroff, Mann, Gliatto, Sullivan, & Campbell, 2001), larger scale studies of the pattern of neuropsychological and psychiatric impairment following recovery from the acute inflammatory phase are less apparent. This paper reports the results of neuropsychological testing with a range of standardised cognitive measures in a case series of long-term post-acute participants. Psychiatric abnormality is examined using the SCL-90-R self-report scale of distress (Derogatis, 1983). We also examined the role of emerging insight in the aetiology of depression in this population. Two clusters of cognitive dysfunction were observed, one group of primarily herpes simplex cases showing a severe generalised deficit across a number of cognitive domains and a second cluster showing a variety of more isolated disorders of executive function. Abnormally high levels of distress were reported by participants, with depression, obsessive-compulsive symptoms, interpersonal sensitivity and phobic anxiety most significantly increased. Depression was found to be least severe in those with most accurate insight into their problems. Examining the correlations between cognitive and psychiatric test results demonstrates a relationship between depression and interpersonal anxiety and specific cognitive measures. Obsessive-compulsive behaviour and phobic anxiety, however, appear to exist independently of the assessed cognitive deficits.

Knowledge of semantic categories in normal aged: Influence of education

Semantic memory seems to resist the effects of time, remaining stable even in more advanced ages.

A review of functional imaging studies on category specificity

A review of 20 functional imaging studies that compared visual processing of natural objects and artifacts in normal subjects is presented. The studies included fulfilled three criteria: (i) they used pictures as stimuli, (ii) they were based on direct contrasts between categories, and (iii) they reported findings in Talairach space. Not a single area is consistently activated for a given category across all studies. In contrast, 11 out of 29 regions are reported activated by both artifacts and natural objects. It is argued that the inconsistency is unlikely to reflect differences between studies in task requirements alone. Rather, the most likely causes of the inconsistency are: (i) adoption of liberal statistical thresholds that may yield false-positive activations, (ii) limited sensitivity due to few observations, and (iii) failure to match categories on confounding variables such as familiarity and visual complexity. Of the most consistent activations found, none appear to be selective for natural objects or artifacts. The findings reviewed are compatible with theories of category specificity that assume a widely distributed conceptual system not organized by category.

Phonemic Fluency, Semantic Fluency, and Difference Scores: Normative Data for Adult Hebrew Speakers

Norms for Hebrew semantic and phonemic fluency were collected in a sample of 369 participants, ranging in age from 18 to 85. Two hundred and sixty nine persons completed both tests and the rest completed only the semantic test. Phonemic fluency was assessed with the use of three letters (bet, gimel, and shin) and semantic fluency with the use of three categories (animals, fruits and vegetables, and vehicles). Scores of individual letters and categories, sum scores, as well as the difference between the semantic and phonemic sum scores are presented for four age groups (18-30, 31-50, 51-70, and 71-85). Results show that age had the greatest effect on fluency performance, level of education was positively correlated to sum scores but contributed little to its prediction beyond the contribution of age, and gender had no significant effect.

Patterns of regional brain hypometabolism associated with knowledge of semantic features and categories in Alzheimer's disease

The study of semantic memory in patients with Alzheimer's disease (AD) has raised important questions about the representation of conceptual knowledge in the human brain. It is still unknown whether semantic memory impairments are caused by localized damage to specialized regions or by diffuse damage to distributed representations within nonspecialized brain areas. To our knowledge, there have been no direct correlations of neuroimaging of in vivo brain function in AD with performance on tasks differentially addressing visual and functional knowledge of living and nonliving concepts. We used a semantic verification task and resting 18-fluorodeoxyglucose positron emission tomography in a group of mild to moderate AD patients to investigate this issue. The four task conditions required semantic knowledge of (1) visual, (2) functional properties of living objects, and (3) visual or (4) functional properties of nonliving objects. Visual property verification of living objects was significantly correlated with left posterior fusiform gyrus metabolism (Brodmann's area [BA] 37/19). Effects of visual and functional property verification for non-living objects largely overlapped in the left anterior temporal (BA 38/20) and bilateral premotor areas (BA 6), with the visual condition extending more into left lateral precentral areas. There were no associations with functional property verification for living concepts. Our results provide strong support for anatomically separable representations of living and nonliving concepts, as well as visual feature knowledge of living objects, and against distributed accounts of semantic memory that view visual and functional features of living and nonliving objects as distributed across a common set of brain areas.

Recognition of category-related visual stimuli in Parkinson's disease: Before and after pharmacological treatment

Visual-sensory dysfunctions and semantic processing impairments are widely reported in Parkinson's disease (PD) research. The present study investigated the category-specific deficit in object recognition as a function of both the semantic category and spatial frequency content of stimuli. In the first experiment, the role of dopamine in object-recognition processing was assessed by comparing PD drug naïve (PD-DN), PD receiving levodopa treatment (PD-LD), and control subjects. Experiment 2 consisted of a retest session for PD drug naïve subjects after a period of pharmacological treatment. All participants completed an identification task which displayed animals and tools at nine levels of filtering. Each object was revealed in a sequence of frames whereby the object was presented at increasingly less-filtered images up to a complete version of the image. Results indicate an impaired identification pattern for PD-DN subjects solely for animal category stimuli. This differential pharmacological therapy effect was also confirmed at retest (experiment 2). Thus, our data suggest that dopaminergic loss has a specific role in category-specific impairment. Two possible hypotheses are discussed that may account for the defective recognition of semantically different objects in PD.

The “hidden” semantic category dissociation in mild-moderate Alzheimer's disease patients

In patients manifesting mild-moderate Alzheimer's disease (AD), lexical semantic tasks are known to be influenced by several variables which should be adequately taken into account when studying semantic category dissociations. The following study provides indexes of three new variables (imageability (I), percentage of name agreement (pNA) and number of target alternatives (nTA)) and investigates their role in naming in a group of people with AD and in matched older adults controls. Forty young healthy participants rated I, pNA and nTA of 155 stimuli (including living and non-living items) from and sets. Forty-eight people with mild-moderate AD and 40 older adults were given the two naming tests and their naming ratings were analysed with a two-way ANOVA (two groupsxtwo categories) to assess category specificity and the effect of interaction. The influence of relevant concomitant variables in naming was measured using a multiple regression analysis. Semi-partial correlations were carried out to assess the independent contribution of each variable to naming. We found that living items were more imageable and had fewer lexical alternatives and higher name agreement than non-living items. We also found that controls significantly named better than AD patients (F=37.551, p<.001), whilst the two-way ANOVA showed no significant effect of category (F=.649, p=.423). Notably category effect emerged when assessing its independent contribution performing a semi-partial correlation (beta=-.278, p<.001) which kept the effect of relevant concomitant variables under control. Our results confirm that category dissociation does emerge in mild-moderate AD patients when the effect of relevant concomitant variables is adequately taken into account. The hypothesis that the highly correlated properties of items from biological categories may play a protective effect on living things, making them less prone to impairment in the early stages of AD, is discussed.

Selective preservation of memory for people in the context of semantic memory disorder: patterns of association and dissociation

A number of single cases in the literature demonstrate that person-specific semantic knowledge can be selectively impaired after acquired brain damage compared with that of object categories. However, there has been little unequivocal evidence for the reverse dissociation, selective preservation of person-specific semantic knowledge. Recently, three case studies have been published which provide support for the claim that such knowledge can be selectively preserved [Kay, J., & Hanley, J. R. (2002). Preservation of memory for people in semantic memory disorder: Further category-specific semantic dissociation. Cognitive Neuropsychology, 19, 113-134; Lyons, F., Hanley, J. R., & Kay, J. (2002). Anomia for common names and geographical names with preserved retrieval of names of people: A semantic memory disorder. Cortex, 38, 23-35; Thompson, S. A, Graham, K. S., Williams, G., Patterson, K., Kapur, N., & Hodges, J. R. (2004). Dissociating person-specific from general semantic knowledge: Roles of the left and right temporal lobes. Neuropsychologia, 42, 359-370]. In this paper, we supply further evidence from a series of 18 patients with acquired language disorder. Of this set, a number were observed to be impaired on tests of semantic association and word-picture matching using names of object categories (e.g. objects, animals and foods), but preserved on similar tests using names of famous people. Careful methodology was applied to match object and person-specific categories for item difficulty. The study also examined whether preservation of person-specific semantic knowledge was associated with preservation of knowledge of 'biological categories' such as fruit and vegetables and animals, or with preservation of 'token' knowledge of singular categories such as countries. The findings are discussed in the context of a variety of accounts that examine whether semantic memory has a categorical structure.

Word Finding in the Damaged Brain: Probing Marshall's Caveat

Marshall (1977) constructed a plausible simulation of "anomic" speech out of the 100 most common words in the English language. He suggested that impaired access to lower frequency vocabulary might underlie anomic word finding difficulties. But he also noted that another factor, age of acquisition, may exert an influence, with anomic patients experiencing particular difficulty with later acquired vocabulary. A review of research on word-finding in aphasia and other neuropsychological conditions suggests that Marshall (1977) may have been right on both counts, and that in many patients both frequency of use and age of acquisition influence the likelihood that a given word will be able to be accessed and used. Theoretical accounts of why the age of acquisition of words might affect their retention or loss following brain injury in adulthood are considered.

Evaluating feature-category relations using semantic fluency tasks

The issue of the relationship between semantic features and semantic categories has been raised by Warrington and colleagues, who claimed that sensory and functional-associative features are differentially important in determining the meaning of living and nonliving things (Warrington & McCarthy, 1983, 1987; Warrington & Shallice, 1984). In the present study, the effectiveness of semantic memory search for living and nonliving things with sensory and functional-associative search cues was evaluated through eight different adaptations of the semantic fluency task. More living thing responses and clusters were generated from sensory than from functional-associative search cues, while the reverse pattern holds for nonliving things responses and clusters. The results thus provide consistent empirical support for the assumption that sensory properties are fundamental in the representation of living things, while functional-associative properties are fundamental in the semantic representation of nonliving things.

The neural organization of semantic memory: Electrophysiological activity suggests feature-based segregation

Despite decades of research, it remains controversial whether semantic knowledge is anatomically segregated in the human brain. To address this question, we recorded event-related potentials (ERPs) while participants viewed pictures of animals and tools. Within the 200-600-ms epoch after stimulus presentation, animals (relative to tools) elicited an increased anterior negativity that, based on previous ERP studies, we interpret as associated with semantic processing of visual object attributes. In contrast, tools (relative to animals) evoked an enhanced posterior left-lateralized negativity that, according to prior research, might reflect accessing knowledge of characteristic motion and/or more general functional properties of objects. These results support the hypothesis of the neuroanatomical knowledge organization at the level of object features: the observed neurophysiological activity was modulated by the features that were most salient for object recognition. The high temporal resolution of ERPs allowed us to demonstrate that differences in processing animals and tools occurred specifically within the time-window encompassing semantic analysis.

The influence of gender and lesion location on naming disorders for animals, plants and artefacts

The aim of this systematic review of single case studies of patients showing a category-specific disorder was to evaluate the influence of gender and lesion location on category-specific disorders for biological versus artefact categories and, within the former, for animals versus plant life categories. Two complementary studies were made, taking into account all the available single case reports of category-specific disorders found in the literature. The first study consisted of an overall statistical evaluation of the influence that gender and lesion location can have upon naming scores obtained with these different categories in patients selected only because they showed some kind of category-specific disorder. The second study assessed the influence of these variables on more selected groups of patients, contrasting those showing a categorical impairment for living things versus artefacts and, respectively, for animals versus plant life categories. Results of these studies consistently showed that: (a) Lesion location has a strong influence on the distinction between biological and artefacts categories, but not on that between animals and plant life domains. In patients with a prevalent impairment either for animals or for plant life items, lesions usually encroach upon the anterior or the posterior parts of the ventral stream of visual processing, whereas in patients with a prevalent impairment for artefacts they are located elsewhere (usually on more dorsal structures of the brain). (b) Gender, on the contrary, does not influence the distinction between living and non-living things, but, within the living entities, has a strong influence on the distinction between animals and plant life. Consistent with data obtained in normal people, which show that men are more familiar with animals and women with fruit and vegetables, men were, indeed, more impaired with plant life categories, whereas women were more impaired with animals.

Hemispheric asymmetries of hypometabolism associated with semantic memory impairment in Alzheimer's disease: a study using positron emission tomography with fluorodeoxyglucose-F18

Considerable disagreement exists about the neuroanatomical basis of conceptual-semantic impairments observed in a subgroup of patients with Alzheimer's disease (AD) at mild to moderate stages of the disease. Several studies of groups of patients have shown correlations between focal hypometabolism or hypoperfusion in left hemispheric areas and measures of verbal semantic memory impairment in AD patients. The question remains, however, whether left hemispheric hypometabolism is sufficient to produce such impairment in the single case and whether nonverbal semantic knowledge is also affected. We used positron emission tomography (PET) with fluorodeoxyglucose-F18 (FDG), statistical parametric mapping (SPM), and tests of verbal and nonverbal semantic memory in 11 AD patients with a mean score on the Mini-Mental State Examination of 22.6 (+/-2.8). Naming impairment was significantly associated with left hemispheric asymmetry of hypometabolism on a single-case basis. Our correlation analysis showed that metabolism in left anterior temporal, posterior inferior temporal, inferior parietal and medial occipital areas (Brodmann areas: 21/38, 37, 40 and 19) correlated with both verbal and nonverbal semantic performance. We conclude that left hemispheric synaptic dysfunction, as measured by regional glucose hypometabolism, was sufficient to produce semantic impairments in our patients. The majority of areas affected in our patients with semantic impairments were involved in multimodal or supramodal (verbal and nonverbal) semantic knowledge.