“Illusions of Normality”: a Methodological Critique of Category-Specific Naming

Investigating the influence of semantic factors on word retrieval: Reservations, results and recommendations

There is consensus that word retrieval starts with activation of semantic representations. However, in adults without language impairment, relatively little attention has been paid to the effects of the semantic attributes of to-be-retrieved words. This paper, therefore, addresses the question of which item-inherent semantic factors influence word retrieval. Specifically, it reviews the literature on a selection of these factors: imageability, concreteness, number of semantic features, typicality, intercorrelational density, featural distinctiveness, concept distinctiveness, animacy, semantic neighbourhood density, semantic similarity, operativity, valence, and arousal. It highlights several methodological challenges in this field, and has a focus on the insights from studies with people with aphasia where the effects of these variables are more prevalent. The paper concludes that further research simultaneously examining the effects of different semantic factors that are likely to affect lexical co-activation, and the interaction of these variables, would be fruitful, as would suitably scaled computational modelling of these effects in unimpaired language processing and in language impairment. Such research would enable the refinement of theories of semantic processing and word production, and potentially have implications for diagnosis and treatment of semantic and lexical impairments.

Category-selective deficits are the exception and not the rule: Evidence from a case-series of 64 patients with ventral occipito-temporal cortex damage

The organisational principles of the visual ventral stream are still highly debated, particularly the relative association/dissociation between word and face recognition and the degree of lateralisation of the underlying processes. Reports of dissociations between word and face recognition stem from single case-studies of category selective impairments, and neuroimaging investigations of healthy participants. Despite the historical reliance on single case-studies, more recent group studies have highlighted a greater commonality between word and face recognition. Studying individual patients with rare selective deficits misses (a) important variability between patients, (b) systematic associations between task performance, and (c) patients with mild, severe and/or non-selective impairments; meaning that the full spectrum of deficits is unknown. The Back of the Brain project assessed the range and specificity of visual perceptual impairment in 64 patients with posterior cerebral artery stroke recruited based on lesion localization and not behavioural performance. Word, object, and face processing were measured with comparable tests across different levels of processing to investigate associations and dissociations across domains. We present two complementary analyses of the extensive behavioural battery: (1) a data-driven analysis of the whole patient group, and (2) a single-subject case-series analysis testing for deficits and dissociations in each individual patient. In both analyses, the general organisational principle was of associations between words, objects, and faces even following unilateral lesions. The majority of patients either showed deficits across all domains or in no domain, suggesting a spectrum of visuo-perceptual deficits post stroke. Dissociations were observed, but they were the exception and not the rule: Category-selective impairments were found in only a minority of patients, all of whom showed disproportionate deficits for words. Interestingly, such selective word impairments were found following both left and right hemisphere lesions. This large-scale investigation of posterior cerebral artery stroke patients highlights the bilateral representation of visual perceptual function.

A standardized set of 3-D objects for virtual reality research and applications

The use of immersive virtual reality as a research tool is rapidly increasing in numerous scientific disciplines. By combining ecological validity with strict experimental control, immersive virtual reality provides the potential to develop and test scientific theories in rich environments that closely resemble everyday settings. This article introduces the first standardized database of colored three-dimensional (3-D) objects that can be used in virtual reality and augmented reality research and applications. The 147 objects have been normed for name agreement, image agreement, familiarity, visual complexity, and corresponding lexical characteristics of the modal object names. The availability of standardized 3-D objects for virtual reality research is important, because reaching valid theoretical conclusions hinges critically on the use of well-controlled experimental stimuli. Sharing standardized 3-D objects across different virtual reality labs will allow for science to move forward more quickly.

On the Relation between Face and Object Recognition in Developmental Prosopagnosia: No Dissociation but a Systematic Association

There is an ongoing debate about whether face recognition and object recognition constitute separate domains. Clarification of this issue can have important theoretical implications as face recognition is often used as a prime example of domain-specificity in mind and brain. An important source of input to this debate comes from studies of individuals with developmental prosopagnosia, suggesting that face recognition can be selectively impaired. We put the selectivity hypothesis to test by assessing the performance of 10 individuals with developmental prosopagnosia on demanding tests of visual object processing involving both regular and degraded drawings. None of the individuals exhibited a clear dissociation between face and object recognition, and as a group they were significantly more affected by degradation of objects than control participants. Importantly, we also find positive correlations between the severity of the face recognition impairment and the degree of impaired performance with degraded objects. This suggests that the face and object deficits are systematically related rather than coincidental. We conclude that at present, there is no strong evidence in the literature on developmental prosopagnosia supporting domain-specific accounts of face recognition.

Naming and Categorization in Healthy Participants: Crowded Domains and Blurred Effects of Gender

The study of category-specific effects has produced compelling insights into the structure, organization and functioning of cognitive processes. According to some accounts, the greater intra-category structural similarity for living things (LT) contributes to faster access to superordinate pictorial information, making LT easier to classify than structurally dissimilar items (i.e., nonliving things: NLT). Conversely, LT would be harder to name than NLT, as they must compete with within-domain structurally similar items in order to be properly discriminated. Additionally, it has been reported that men perform better with NLT than women, whereas women surpass men with LT but the reasons for this remain unclear. In the current study, we explored both the visual crowding hypothesis and the effects of gender by testing the performance of 40 healthy participants in classification and naming tasks. Analyses revealed that LT were classified significantly faster than NLT (η p 2 = .11), but named significantly slower (η p 2 = .25). Interestingly, the same results persisted after removing atypical categories that are known to distort the interpretation of data from the analyses. Moreover, we did not find the expected effects of gender. Men were more accurate than women naming NLT (η p 2 = .13), and women did not surpass men in any task.

On Colour, Category Effects, and Alzheimer's Disease: A Critical Review of Studies and Further Longitudinal Evidence

The role of colour in object recognition is controversial; in this study, a critical review of previous studies, as well as a longitudinal study, was conducted. We examined whether colour benefits the ability of Alzheimer's disease (AD) patients and normal controls (NC) when naming items differing in colour diagnosticity: living things (LT) versus nonliving things (NLT). Eleven AD patients were evaluated twice with a temporal interval of 3 years; 26 NC were tested once. The participants performed a naming task (colour and greyscale photographs); the impact of nuisance variables (NVs) and potential ceiling effects were also controlled. Our results showed that (i) colour slightly favoured processing of items with higher colour diagnosticity (i.e., LT) in both groups; (ii) AD patients used colour information similarly to NC, retaining this ability over time; (iii) NVs played a significant role as naming predictors in all the participants, relegating domain to a minor plane; and (iv) category effects (better processing of NLT) were present in both groups. Finally, although patients underwent semantic longitudinal impairment, this was independent of colour deterioration. This finding provides better support to the view that colour is effective at the visual rather than at the semantic level of object processing.

Bank of Standardized Stimuli (BOSS) phase II: 930 new normative photos

Researchers have only recently started to take advantage of the developments in technology and communication for sharing data and documents. However, the exchange of experimental material has not taken advantage of this progress yet. In order to facilitate access to experimental material, the Bank of Standardized Stimuli (BOSS) project was created as a free standardized set of visual stimuli accessible to all researchers, through a normative database. The BOSS is currently the largest existing photo bank providing norms for more than 15 dimensions (e.g. familiarity, visual complexity, manipulability, etc.), making the BOSS an extremely useful research tool and a mean to homogenize scientific data worldwide. The first phase of the BOSS was completed in 2010, and contained 538 normative photos. The second phase of the BOSS project presented in this article, builds on the previous phase by adding 930 new normative photo stimuli. New categories of concepts were introduced, including animals, building infrastructures, body parts, and vehicles and the number of photos in other categories was increased. All new photos of the BOSS were normalized relative to their name, familiarity, visual complexity, object agreement, viewpoint agreement, and manipulability. The availability of these norms is a precious asset that should be considered for characterizing the stimuli as a function of the requirements of research and for controlling for potential confounding effects.

From word superiority to word inferiority: visual processing of letters and words in pure alexia

Visual processing and naming of individual letters and short words were investigated in four patients with pure alexia. To test processing at different levels, the same stimuli were studied across a naming task and a visual perception task. The normal word superiority effect was eliminated in both tasks for all patients, and this pattern was more pronounced in the more severely affected patients. The relationship between performance with single letters and words was, however, not straightforward: One patient performed within the normal range on the letter perception task, while being severely impaired in letter naming and word processing, and performance with letters and words was dissociated in all four patients, with word reading being more severely impaired than letter recognition. This suggests that the word reading deficit in pure alexia may not be reduced to an impairment in single letter perception.

Is there a semantic system for abstract words?

Two views on the semantics of concrete words are that their core mental representations are feature-based or are reconstructions of sensory experience. We argue that neither of these approaches is capable of representing the semantics of abstract words, which involve the representation of possibly hypothetical physical and mental states, the binding of entities within a structure, and the possible use of embedding (or recursion) in such structures. Brain based evidence in the form of dissociations between deficits related to concrete and abstract semantics corroborates the hypothesis. Neuroimaging evidence suggests that left lateral inferior frontal cortex supports those processes responsible for the representation of abstract words.

Types of case series--the anatomically based approach: commentary on M. F. Schwartz & G. S. Dell: case series investigations in cognitive neuropsychology

The paper addresses a weakness in the Schwartz and Dell paper (2010)-namely, its discussion of the inclusion criteria for case series. The paper distinguishes the different types that exist and how they constrain the theoretical conclusions that one can draw about the organization of the normal cognitive system. Four different types of inclusion criteria are considered. Two are those treated by Schwartz and Dell-namely, theoretically derived clinical criteria, such as the example of semantic dementia, and broad clinical criteria such as the presence of aphasia. In addition, in the present paper two different types of anatomically based criteria are assessed-those using anatomical regions selected a priori and also regions selected as a result of an anatomical group study analysis. Putative functional syndromes are argued to be the empirical building blocks for cognitive neuropsychology. Anatomically based case series can aid in their construction or in their fractionation.

An ecological alternative to Snodgrass & Vanderwart: 360 high quality colour images with norms for seven psycholinguistic variables

This work presents a new set of 360 high quality colour images belonging to 23 semantic subcategories. Two hundred and thirty-six Spanish speakers named the items and also provided data from seven relevant psycholinguistic variables: age of acquisition, familiarity, manipulability, name agreement, typicality and visual complexity. Furthermore, we also present lexical frequency data derived from Internet search hits. Apart from the high number of variables evaluated, knowing that it affects the processing of stimuli, this new set presents important advantages over other similar image corpi: (a) this corpus presents a broad number of subcategories and images; for example, this will permit researchers to select stimuli of appropriate difficulty as required, (e.g., to deal with problems derived from ceiling effects); (b) the fact of using coloured stimuli provides a more realistic, ecologically-valid, representation of real life objects. In sum, this set of stimuli provides a useful tool for research on visual object- and word-processing, both in neurological patients and in healthy controls.

The loss of conceptual associations in mild Alzheimer's dementia

Changes in semantic memory are a controversial topic in research on cognitive decline in aging. In this study, we analyzed whether the semantic deficits in mild Alzheimer's disease (AD) reflect the information acquisition process, and whether the deficits are related to when the information was initially stored. We hypothesized that in the earlier stages of dementia, the ability to access semantic associative relations reflects the use of these associations during different developmental stages. Specifically, we asserted that Alzheimer's patients might be able to access the relations that are learned earlier in life for the longest amount of time compared to those that are learned later. In this study, 254 subjects were divided into four groups (child, adult, senior, and Alzheimer's patients groups) and were evaluated with an experimental semantic association task that incorporated five semantic associative relations that were used to compare performance by age group. An analysis of variance (ANOVA) 4 × 5 test showed a significant main group effect, F(3, 250) = 97.1, p < .001, and an associative relations effect, F(4, 1000) = 23.1, p < .001, as well as an interaction of Group × Associative Relations, F(12, 1000) = 8.5, p < .001. The results demonstrated that the semantic associative relations that were acquired in later developmental stages were less preserved in persons with mild AD (i.e., superordinate relation, p < .0001). On the contrary, the semantic relations acquired earlier in childhood were better preserved in persons with mild AD. Our results suggest that semantic impairment begins with difficulties in using the associative relations that link concepts together in the semantic memory of patients with mild AD dementia (and possibly in individuals with mild cognitive impairment).

A set of high quality colour images with Spanish norms for seven relevant psycholinguistic variables: the Nombela naming test

This paper presents a new corpus of 140 high quality colour images belonging to 14 subcategories and covering a range of naming difficulty. One hundred and six Spanish speakers named the items and provided data for several psycholinguistic variables: age of acquisition, familiarity, manipulability, name agreement, typicality and visual complexity. Furthermore, we also present lexical frequency data derived internet search hits. Apart from the large number of variables evaluated, these stimuli present an important advantage with respect to other comparable image corpora in so far as naming performance in healthy individuals is less prone to ceiling effect problems. Reliability and validity indexes showed that our items display similar psycholinguistic characteristics to those of other corpora. In sum, this set of ecologically valid stimuli provides a useful tool for scientists engaged in cognitive and neuroscience-based research.

Size matters: a study on naming and size knowledge in dementia of the Alzheimer type

Category-specificity was longitudinally studied over a period of 12 months in seven Alzheimer disease patients, with two semantic tasks differing with respect to verbal processing demands: picture naming and a size ordering task. Items from each task were matched on all cognitive and psycholinguistic variables known to differ across domains (living-nonliving). Naming performance of patients was poorer than that of normal controls. Regarding category-specific effects, while naming performance of patients was parallel to that of normal controls, patients' performance with the size ordering task revealed a different scaling of living things while that of nonliving things mirrored performance of normal controls. This suggests that caution is needed when the picture naming task is exclusively used to document category-specific effects.

Naming manipulable objects: anatomy of a category specific effect in left temporal tumours

Whether semantic knowledge is categorically organized or is based in an undifferentiated distributed network within the temporal lobes or it is at least partially organized in property-based networks is still an open issue. With a naming task involving living and nonliving entities, the latter divided according to degree of manipulability, we studied a group of 30 tumour patients with either right, left anterior or left posterior temporal lobes' lesions and a herpes simplex encephalitis patient (MU). Both cross-subject and cross-stimulus analyses were conducted. Left hemisphere patients were overall worse than both right hemisphere patients and controls in the naming task. They moreover named nonliving items worse than living. This effect was larger in left posterior temporal than both right temporal and also left anterior temporal patients and significant both at a cross-subject and cross-stimulus levels of analysis. In addition the left posterior temporal group had more difficulties with highly manipulable objects than left anterior temporal patients, but the effect was significant only on a cross-subject analysis. VLSM lesion analysis revealed that the area most critically associated with the larger naming deficit for manipulable objects was the posterior superior portion of the left temporal lobe, particularly the posterior middle temporal gyrus. These results support a 'property-based networks' account of semantic knowledge rather than an 'undifferentiated network' account. For manipulable objects, this would be a posterior-temporal/inferior-parietal left hemisphere "action/manipulation-property-based" network related to the dorsal pathways which is thought to be important in action control, as suggested by neuroimaging results.

Category-specificity in visual object recognition

Are all categories of objects recognized in the same manner visually? Evidence from neuropsychology suggests they are not: some brain damaged patients are more impaired in recognizing natural objects than artefacts whereas others show the opposite impairment. Category-effects have also been demonstrated in neurologically intact subjects, but the findings are contradictory and there is no agreement as to why category-effects arise. This article presents a pre-semantic account of category-effects (PACE) in visual object recognition. PACE assumes two processing stages: shape configuration (the binding of shape elements into elaborate shape descriptions) and selection (among competing representations in visual long-term memory), which are held to be differentially affected by the structural similarity between objects. Drawing on evidence from clinical studies, experimental studies with neurologically intact subjects and functional imaging studies, it is argued that PACE can account for category-effects at both behavioural and neural levels in patients and neurologically intact subjects. The theory also accounts for the way in which category-effects are affected by different task parameters (the degree of perceptual differentiation called for), stimulus characteristics (whether stimuli are presented as silhouettes, full line-drawings, or fragmented forms), stimulus presentation (stimulus exposure duration and position) as well as interactions between these parameters.

The impact of dementia, age and sex on category fluency: greater deficits in women with Alzheimer's disease

A category specific effect in naming tasks has been reported in patients with Alzheimer's dementia. Nonetheless, naming tasks are frequently affected by methodological problems, e.g., ceiling effects for controls and "nuisance variables" that may confound results. Semantic fluency tasks could help to address some of these methodological difficulties, because they are not prone to producing ceiling effects and are less influenced by nuisance variables. One hundred and thirty-three participants (61 patients with probable AD; and 72 controls: 36 young and 36 elderly) were evaluated with semantic fluency tasks in 14 semantic categories. Category fluency was affected both by dementia and by age: while in nonliving-thing categories there were differences among the three groups, in living thing categories larger lexical categories produced bigger differences among groups. Sex differences in fluency emerged, but these were moderated both by age and by pathology. In particular, fluency was smaller in female than male Alzheimer patients for almost every subcategory.

Conceptual knowledge in the brain: fMRI evidence for a featural organization

The organization and representation of conceptual knowledge in the brain remains a controversial issue in terms of both neuropsychological and imaging evidence. We report the results of a functional magnetic resonance study in which the role of the most debated dimensions (domain and feature type) was evaluated through a concept-feature verification task. The scope of the task was to eliminate serious methodological concerns that weighed down previous imaging research in this area, and to allow more definitive conclusions regarding the specific contribution of these dimensions. The results show differential patterns of brain activity according to feature type (both motion and visual form/surface features) but not according to concept domain (living vs. nonliving things). These findings are in accord with a modality-specific account of conceptual knowledge organization in the brain, in which specific kinds of features (e.g. form, color, motion, etc) have differential importance for representing different concepts.

A predominance of category deficits for living things in Alzheimer's disease and Lewy body dementia

Although semantic memory impairment is well documented in patients with dementia of the Alzheimer's type, questions remain as to whether the deficit extends to other forms of dementia and whether it differentially affects different domains of knowledge. We examined category naming on two tasks (picture naming and naming-to-description) in patients with Alzheimer's disease (AD: n = 11), Lewy body dementia (DLB: n = 11) and healthy elderly matched controls (n = 22). The DLB and AD groups showed significantly worse naming on both tasks, although the AD patients were more impaired than the DLB patients. Like some AD patients, some DLB patients showed evidence of category-specific naming deficits, and strikingly, all 25 significant category dissociations were for living things. The latter finding accords with the preponderance of living deficits previously documented for AD patients, but extends this finding to DLB patients. The implications of this category bias is discussed in relation to relevant models of category specificity.

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.

A meta-analytic review of category naming in Alzheimer's disease

Patients with Alzheimer's disease (AD) experience word-finding difficulties that become increasingly pronounced as pathological changes accrue in the brain. One question that has received increasing attention over the last two decades concerns whether the anomia in AD is category-specific, i.e. differentially affects the ability to name living things (LT) and non-living things (NLT). The current meta-analysis systematically reviewed the effect sizes for naming pictures of LT and NLT in comparisons of AD patients and healthy controls in 21 studies with over 1000 participants (557 patients and 509 healthy controls). A random effects model analysis revealed no significant difference in the large weighted effect sizes for naming pictures of LT and NLT (d=1.76 and 1.49, respectively). Moderator variable analyses revealed a significant impact of stimulus colour on the effect size for LT, indicating that using colour stimuli significantly increases the impairment of naming LT in AD patients. Additionally, we found that LT and the NLT effect sizes were larger for samples with proportionally more female patients; smaller samples produced larger LT effect sizes. In contrast, effect sizes were not significantly related to dementia severity, patient age, the number of stimuli, years of education, or the number of matching variables controlled.

An attenuation of the 'normal' category effect in patients with Alzheimer's disease: a review and bootstrap analysis

There is a consensus that Alzheimer's disease (AD) impairs semantic information, with one of the first markers being anomia i.e. an impaired ability to name items. Doubts remain, however, about whether this naming impairment differentially affects items from the living and nonliving knowledge domains. Most studies have reported an impairment for naming living things (e.g. animals or plants), a minority have found an impairment for nonliving things (e.g. tools or vehicles), and some have found no category-specific effect. A survey of the literature reveals that this lack of agreement may reflect a failure to control for intrinsic variables (such as familiarity) and the problems associated with ceiling effects in the control data. Investigating picture naming in 32 AD patients and 34 elderly controls, we used bootstrap techniques to deal with the abnormal distributions in both groups. Our analyses revealed the previously reported impairment for naming living things in AD patients and that this persisted even when intrinsic variables were covaried; however, covarying control performance eliminated the significant category effect. Indeed, the within-group comparison of living and nonliving naming revealed a larger effect size for controls than patients. We conclude that the category effect in Alzheimer's disease is no larger than is expected in the healthy brain and may even represent a small diminution of the normal profile.

Domain-specific deficits in schizophrenia

INTRODUCTION

Object recognition deficits are well documented in certain neurological disorders (e.g., Alzheimer's disease, herpes simplex encephalitis). Although agnosic problems have been documented in some patients with schizophrenia (Gabrovska et al., 2003), no study has investigated whether such deficits differentially affect specific categories of information (as they sometimes do in neurological cases).

METHOD

In Part I of this study, we compared object recognition in 55 patients with chronic schizophrenia and 22 age- and NART IQ-matched healthy controls. In Part II, we present a detailed case study of one patient with schizophrenia (DH) who displays a severe category specific semantic knowledge for living things.

RESULTS

Of the patients with schizophrenia, 75% had object recognition below the 5th percentile, and in 11% of cases, a highly specific classical category dissociation emerged (5 cases with nonliving deficit and 1 with living deficit); and two other patients showed strong dissociation for living things. These findings provide convincing evidence of a classical double dissociation across the two categories. In Part II, the in-depth case study of one schizophrenic patient (DH), documented a profound agnosia for living things. While DH displayed intact low level perceptual and spatial ability and could copy drawings, he was severely impaired at naming, picture-name matching, semantic fluency, and could not describe or draw items from memory.

CONCLUSIONS

The presence of impaired object recognition in most schizophrenic patients, along with highly selective category specific deficits in a minority, is discussed with reference to similar findings in neurological patients.

The impact of colour, spatial resolution, and presentation speed on category naming

Studies of neurological patients with category-specific agnosia have provided important contributions to our understanding of object recognition, although the meaning of such disorders is still hotly debated. One crucial line of research for our understanding of category effects, is through the examination of category biases in healthy normal subjects. This approach has, however, led to contradictory findings with advantages both for natural kinds and for man-made things being documented in healthy subjects. It has been proposed that task conditions may influence the direction of advantage (Gerlach, 2001) and in particular, that sub-optimal viewing conditions underpin natural kinds advantages, while man-made advantages emerge under more optimal viewing conditions. In two experiments with normal subjects, we examined the roles played by spatial resolution (blurring), stimulus type (colour and texture), and speed of presentation in picture naming across category. In both experiments, healthy subjects showed a natural kind advantage for original stimuli and for blurred colour stimuli (at slow and fast presentation speeds), while an advantage for man-made things emerged for line-drawings that were blurred and presented slowly. The implications for category-specific object recognition deficits are discussed.

Category-specificity can emerge from bottom-up visual characteristics: Evidence from a modular neural network

The role of bottom-up visual processes in category-specific object recognition has been largely unexplored. We examined the role of low-level visual characteristics in category specific recognition using a modular neural network comprising both unsupervised and supervised components. One hundred standardised pictures from ten different categories (five living and five nonliving, including body parts and musical instruments) were presented to a Kohonen self-organising map (SOM) which re-represents the visual stimuli by clustering them within a smaller number of dimensions. The SOM representations were then used to train an attractor network to learn the superordinate category of each item. The ease with which the model acquired the category mappings was investigated with respect to emerging category effects. We found that the superordinates could be separated by very low-level visual factors (as extracted by the SOM). The model also accounted for the well documented atypicality of body parts and musical instrument superordinates. The model has clear relevance to human object recognition since the model was quicker to learn more typical category exemplars and finally the model also accounted for more than 20% of the naming variance in a sample of 57 brain injured subjects. We conclude that purely bottom-up visual characteristics can explain some important features of category-specific phenomena.

Crowded and sparse domains in object recognition: Consequences for categorization and naming

Some models of object recognition propose that items from structurally crowded categories (e.g., living things) permit faster access to superordinate semantic information than structurally dissimilar categories (e.g., nonliving things), but slower access to individual object information when naming items. We present four experiments that utilize the same matched stimuli: two examine superordinate categorization and two examine picture naming. Experiments 1 and 2 required participants to sort pictures into their appropriate superordinate categories and both revealed faster categorization for living than nonliving things. Nonetheless, the living thing superiority disappeared when the atypical categories of body parts and musical instruments were excluded. Experiment 3 examined naming latency and found no difference between living and nonliving things. This finding was replicated in Experiment 4 where the same items were presented in different formats (e.g., color and line-drawn versions). Taken as a whole, these experiments show that the ease with which people categorize items maps strongly onto the ease with which they name them.

Anatomical functional and cognitive determinants of semantic memory disorders

Contemporary debates on the 'semantic memory' construct revolve around three main topics: (1) the functional and anatomical relationships between episodic and semantic memory; (2) the format of semantic representations and their relationships with the underlying sensory-motor processes; (3) the categorical organization of semantic memory. The aim of the present review is to demonstrate that there is a common thread linking these different aspects of semantic memory. This thread is represented by the interdependence of mechanisms involved in the construction of semantic memory and the content of semantic representations. In particular, I suggest there is a continuity between: (a) the mechanisms of acquisition of episodic and semantic memory; (b) semantic representations and sensory-motor processes preliminary to the acquisition of these representations. This continuity has important implications for the format of semantic representations and the brain structures subserving the organisation of various categories of knowledge.

An ERP study of low and high relevance semantic features

It is believed that the N400 elicited by concepts belonging to living is larger than N400 to non-living. This is considered as evidence that concepts are organized, in the brain, on the basis of categories. We conducted a feature-verification experiment where living and non-living concepts were matched for relevance of semantic features. Relevance is a measure of the contribution of semantic features to the "core" meaning of a concept. We found that when relevance is low the N400 is large. In addition, we found that when the two categories of living and non-living are equated for relevance the seemingly category effect at behavioral and neural level disappeared. In sum, N400 is sensitive, rather than to categories, to semantic features, thus showing that previously reported effects of semantic categories may arise as a consequence of the differing relevance of concepts belonging to living and non-living categories.