Category-specific Disorders Research Articles

Using representational similarity analysis to reveal category and process specificity in visual object recognition

Cross-condition comparisons on neurodevelopmental conditions are central in neurodiversity research. In the realm of visual perception, the performance of participants with different category-specific disorders such as developmental prosopagnosia (problems with faces) and dyslexia (problems with words) have contributed to understanding of perceptual processes involved in word and face recognition. Alterations in face and word recognition are present in several neurodiverse populations, and improved knowledge about their relationship may increase our understanding of this variability of impairment. The present study investigates organizing principles of visual object processing and their implications for developmental disorders of recognition. Some accounts suggest that distinct mechanisms are responsible for recognizing objects of different categories, while others propose that categories share or even compete for cortical resources. We took an individual differences approach to estimate the relationship between abilities in recognition. Neurotypical participants (N = 97 after outlier exclusion) performed a match-to-sample task with faces, houses, and pseudowords. Either individual features or feature configurations were manipulated. To estimate the separability of visual recognition mechanisms, we used representational similarity analysis (RSA) where correlational matrices for accuracy were compared to predicted data patterns. Recognition abilities separated into face recognition on one hand and house/pseudoword recognition on the other, indicating that face recognition may rely on relatively selective mechanisms in neurotypicals. We also found evidence for a general visual object recognition mechanism, while some combinations of category (faces, houses, words) and processing type (featural, configural) likely rely on additional mechanisms. Developmental conditions may therefore reflect combinations of impaired and intact aspects of specific and general visual object recognition mechanisms, where featural and configural processes for one object category separate from the featural or configural processing of another. More generally, RSA is a promising approach for advancing understanding of neurodiversity, including shared aspects and distinctions between neurodevelopmental conditions of visual recognition.

What a pooled data study tells us about the relationships between gender and knowledge of semantic categories

ABSTRACTIntroduction: Both the neuropsychological study of patients with category-specific semantic disorders (CSSD) and the experimental research on categorical processing in healthy subjects (HSs) have shown that men are mainly impaired with fruits and vegetables and women with animals and artifacts. Since this difference is more striking in patients with CSSD than in HSs, we hypothesized that the lack of power of some investigations conducted with HSs and the different methods used in studies conducted with HSs and patients with CSSD could explain some of these inconsistencies and that a study conducted with a very large number of HSs using visual naming tasks should strongly confirm the role of gender in categorical tasks.Methods: Picture naming data gathered during the last ten years with our category-specificity paradigm from a large number (702) of HSs were reanalyzed.Results: As predicted, men named significantly more animals and artifacts, while women named more plant life items.Discussion: These data confirm that, if different domains of knowledge are studied in a very large sample of HSs using a picture naming task equivalent to the naming tasks used in most anatomo-clinical studies on CSSD, then the gender effects are highly significant.

Re-Evaluation of Attractor Neural Network Model to Explain Double Dissociation in Semantic Memory Disorder

Structure of semantic memory was investigated in the way of neural network simulations in detail. In the literature, it is well-known that brain damaged patients often showed category specific disorder in various cognitive neuropsychological tasks like picture naming, categorisation, identification tasks and so on. In order to describe semantic memory disorder of brain damaged patients, the attractor neural network model originally proposed Hinton and Shallice (1991) was employed and was tried to re-evaluate the model performance. Especially, in order to answer the question about organization of semantic memory, how our semantic memories are organized, computer simulations were conducted. After the model learned data set (Tyler, Moss, Durrant-Peatfield, & Levy, 2000), units in hidden and cleanup layers were removed and observed its performances. The results showed category specificity. This model could also explain the double dissociation phenomena. In spite of the simplicity of its architecture, the attractor neural network might be considered to mimic human behavior in the meaning of semantic memory organization and its disorder. Although this model could explain various phenomenon in cognitive neuropsychology, it might become obvious that this model had one limitation to explain human behavior. As far as investigation in this study, asymmetry in category specificity between animate and inanimate objects might not be explained on this model without any additional assumptions. Therefore, further studies must be required to improve our understanding for semantic memory organisation.

Controversies over the mechanisms underlying the crucial role of the left fronto-parietal areas in the representation of tools

Anatomo-clinical and neuroimaging data show that the left fronto-parietal areas play an important role in representing tools. As manipulation is an important source of knowledge about tools, it has been assumed that motor activity explains the link between tool knowledge and the left fronto-parietal areas. However, controversies exist over the exact mechanisms underlying this relationship. According to a strong version of the “embodied cognition theory,” activation of a tool concept necessarily involves re-enactment of the corresponding kind of action. Impairment of the ability to use tools should, therefore, lead to impairment of tool knowledge. Both the “domains of knowledge hypothesis” and the “sensory-motor model of conceptual knowledge” refute the strong version of the “embodied cognition hypothesis” but acknowledge that manipulation and other action schemata play an important role in our knowledge of tools. The basic difference between these two models is that the former is based on an innate model and the latter holds that the brain’s organization of categories is experience dependent. Data supporting and arguing against each of these models are briefly reviewed. In particular, the following lines of research, which argue against the innate nature of the brain’s categorical organization, are discussed: (1) the observation that in patients with category-specific disorders the semantic impairment does not respect the boundaries between biological entities and artifact items; (2) data showing that experience-driven neuroplasticity in musicians is not confined to alterations of perceptual and motor maps but also leads to the establishment of higher-level semantic representations for musical instruments; (3) results of experiments using previously unfamiliar materials showing that the history of our sensory-motor experience with an object significantly affects its neural representation.

An Italian battery for the assessment of semantic memory disorders

We report the construction and standardization of a new comprehensive battery of tests for the assessment of semantic memory disorders. The battery is constructed on a common set of 48 stimuli, belonging to both living and non-living categories, rigidly controlled for several confounding variables, and is based on an empirically derived corpus of semantic features. It includes six tasks, in order to assess semantic memory through different modalities of input and output: two naming tasks, one with colored pictures and the other in response to an oral description, a word-picture matching task, a picture sorting task, a free generation of features task and a sentence verification task. Normative data on 106 Italian subjects pooled across homogenous subgroups for age, sex and education are reported. The new battery allows an in-depth investigation of category-specific disorders and of progressive semantic memory deficits at features level, overcoming some of the limitations of existing tests.

Premorbid expertise produces category-specific impairment in a domain-general semantic disorder

For decades, category-specific semantic impairment – i.e., better comprehension of items from one semantic category than another – has been the driving force behind many claims about the organisation of conceptual knowledge in the brain. Double dissociations between patients with category-specific disorders are widely interpreted as showing that different conceptual domains are necessarily supported by functionally independent systems. We show that, to the contrary, even strong or classical dissociations can also arise from individual differences in premorbid expertise. We examined two patients with global and progressive semantic degradation who, unusually, had known areas of premorbid expertise. Patient 1, a former automotive worker, showed selective preservation of car knowledge, whereas Patient 2, a former botanist, showed selective preservation of information about plants. In non-expert domains, these patients showed the typical pattern: i.e., an inability to differentiate between highly similar concepts (e.g., rose and daisy), but retention of broader distinctions (e.g., between rose and cat). Parallel distributed processing (PDP) models of semantic cognition show that expertise in a particular domain increases the differentiation of specific-level concepts, such that the semantic distance between these items resembles non-expert basic-level distinctions. We propose that these structural changes interact with global semantic degradation, particularly when expert knowledge is acquired early and when exposure to expert concepts continues during disease progression. Therefore, category-specific semantic impairment can arise from at least two distinct mechanisms: damage to representations that are critical for a particular category (e.g., knowledge of hand shape and action for the category ‘tools’) and differences in premorbid experience.

A General Framework for OWL-Based Concept Similarity

In this paper we propose a general framework for computing similarity between concepts. This framework generalizes the Tversky’s model of similarity and uses a non-negative matrix factorization procedure to estimate abstract classes on which similarity between concepts may be computed. We applied the framework to semantic features used to describe concepts. Experimental results suggest that the general framework is feasible and this method is applicable across different concepts. This framework may be considered as a valuable measurement method to test hypotheses about category-specific disorders.

Monkeys Quickly Learn and Generalize Visual Categories without Lateral Prefrontal Cortex

Categorization is a basic mental process that helps individuals distinguish among groups of negative and positive objects, e.g., poisons and nutrients, or predators and prey. Monkey experiments have suggested that lateral prefrontal cortex (LPFC) participates in learning and processing visual categories. However, in humans category specific visual agnosia follows inferior temporal cortex but not LPFC damage. Here, we use a new behavioral approach to show that both normal monkeys and those with bilateral removal of LPFC learn and generalize perceptual categories of related visual stimuli rapidly without explicit instruction. These results strongly indicate that visual categorization occurs at some earlier stage of feed-forward processing, presumably in temporal cortex, without top-down information from LPFC.

Does normal processing provide evidence of specialised semantic subsystems?

Category-specific disorders are frequently explained by suggesting that living and non-living things are processed in separate subsystems (e.g. Caramazza & Shelton, 1998). If subsystems exist, there should be benefits for normal processing, beyond the influence of structural similarity. However, no previous study has separated the relative influences of similarity and semantic category. We created novel examples of living and non-living things so category and similarity could be manipulated independently. Pre-tests ensured that our images evoked appropriate semantic information and were matched for familiarity. Participants were trained to associate names with the images and then performed a name-verification task under two levels of time pressure. We found no significant advantage for living things alongside strong effects of similarity. Our results suggest that similarity rather than category is the key determinant of speed and accuracy in normal semantic processing. We discuss the implications of this finding for neuropsychological studies.

Conceptions of objects across categories: Childhood patterns resemble those of adults

Studies of category-specific disorders have suggested that categories of living and non-living things vary in the properties that are most salient to recognition. Studies of the object features generated by normal adults have also revealed different patterns of responses to different categories. These adult patterns are likely to originate in childhood, but there are few reports of children's verbal conceptions of objects, and none at present of objects from different categories. This paper investigates the development of object conceptions, in a large group of children, aged 3 years 7 months to 11 years 6 months, in response to 'What is a -- ?' questions directed to 72 objects, selected from two categories of living things (animals and fruit/vegetables) and two categories of artifacts (implements and vehicles). Proportions of perceptual-to-functional features provided by the children to living and non-living things varied with the range of features defined as functions, just as studies of adults have found. Apart from the distribution of superordinate responses, which were significantly more salient to living than to non-living categories, no other property separated the two categories. Only the category of implements could be distinguished from the other categories on the basis of the features generated. It is argued that the perceptual-functional theory of category-specific disorders receives little support from this study, but that in general the distribution of features generated by young children is similar to that produced by normal adults.

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.

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

Category-specific disorders are perhaps the archetypal example of domain-specificity — being typically defined by the presence of dissociations between living and nonliving naming ability in people following neurological damage. The methods adopted to quantify naming across categories are therefore pivotal since they provide the criterion for defining whether patients have a category effect and necessarily influence the subsequent direction and the interpretation of testing. This paper highlights a series of methodological concerns relating to how we measure and define category (or any) dissociations. These include the common failure to include control data or the use of control data that is inappropriate e.g. at ceiling, unmatched. A review of past cases shows that the overwhelming majority suffers from these problems and therefore challenges conclusions about the purported empirical demonstrations of dissociations and double dissociations in the category specific literature. This is not a refutation of category deficits, but skepticism about the current existence of any convincing empirical demonstrations of category specific double dissociations. As a potential solution, certain minimal criteria are proposed that might aid with the attempt to document category effects that are more methodologically convincing.

When is Category Specific in Alzheimer's Disease?

Mixed findings have emerged concerning whether category-specific disorders occur in Alzheimer's disease. Factors that may contribute to these inconsistencies include: ceiling effects / skewed distributions for control data in some studies; differences in the severity of cognitive deficit in patients; and differences in the type of analysis (in particular, if and how controls are used to analyse single case data).We examined picture naming in Alzheimer's patients and matched elderly healthy normal controls in three experiments. These experiments used stimuli that did and did not produce ceiling effects / skewed data in controls. In Experiment 1, we examined for category effects in individual DAT patients using commonly used analyses for single cases (χ 2 and z-scores). The different techniques produced quite different outcomes. In Experiment 2a, we used the same techniques on a different group of patients with similar outcomes. Finally, in Experiment 2b, we examined the same patients but (a) used stimuli that did not produce ceiling effects / skewed distributions in healthy controls, and (b) used statistical methods that did not treat the control sample as a population. We found that ceiling effects in controls may markedly inflate the incidence of dissociations in which living things are differentially impaired and seriously underestimate dissociations in the opposite direction. In addition, methods that treat the control sample as a population led to inflation in the overall number of dissociations detected. These findings have implications for the reliability of category effects previously reported both in Alzheimer patients and in other pathologies. In particular, they suggest that the greater proportion of living than nonliving deficits reported in the literature may be an artifact of the methods used.

Structural similarity and category-specificity: a refined account

It has been suggested that category-specific recognition disorders for natural objects may reflect that natural objects are more structurally (visually) similar than artefacts and therefore more difficult to recognize following brain damage. On this account one might expect a positive relationship between blood flow and structural similarity in areas involved in visual object recognition. Contrary to this expectation we report a negative relationship in that identification of articles of clothing cause more extensive activation than identification of vegetables/fruit and animals even though items from the categories of animals and vegetables/fruit are rated as more structurally similar than items from the category of articles of clothing. Given that this pattern cannot be explained in terms of a tradeoff between activation and accuracy, we interpret these findings within a model where the matching of visual forms to memory incorporates two operations: (i) the integration of stored object features into whole object representations (integral units), and (ii) the competition between activated integral units for selection (i.e. identification). In addition, we suggest that these operations are differentially affected by structural similarity in that high structural similarity may be beneficial for the integration of stored features into integral units, thus explaining the greater activation found with articles of clothing, whereas it may be harmful for the selection process proper because a greater range of candidate integral units will be activated and compete for selection, thus explaining the higher error rate associated with animals. We evaluate the model based on previous evidence from both normal subjects and patients with category-specific disorders and argue that this model can help reconcile otherwise conflicting data.

Heterogeneity is a Fact of Category-Specific Semantic Deficits. So? Comments on Rosazza, Imbornone, Zorzi, Farina, Chiavari, and Cappa (2003)

The Sensory/Functional Theory, until recently the received explanation of category-specific semantic deficits, has been shown to be at variance with various facts that have emerged about the nature of these deficits. In this context, Rosazza, Imbornone, Zorzi, Farina, Chiavari, and Cappa (2003: The Heterogeneity of Category-Specific Semantic Disorders: Evidence from a New Case. Neurocase, 9, 189–202.) report the case study of a patient, MA, with a purported category-specific semantic deficit for living things compared to nonliving things, and an associated modality-specific impairment that differentially affected visual/perceptual compared to functional/associative knowledge. While acknowledging that the Sensory/Functional Theory cannot account for the existence of category-specific semantic deficits, Rosazza and colleagues (2003) contend that “… the presence of a more severe loss of specific visual rather than functional knowledge could support an interpretation according to the Sensory/Functional Theory” [sic] (p. 200). Our comments are divided into two parts. First, we point out that there is an asymmetry between evidence and theory: if there is clear evidence that “disconfirms” a given theory, evidence that is consistent with the theory cannot be argued to support the theory. Second, we argue that the performance profile of MA could potentially be relevant to other interpretations of category-specific deficits but that theoretical interpretations of the performance profile of patient MA are undermined by a lack of methodological rigor, as well as the generally weak data associated with the case.

Structural similarity and category-specificity: a refined account

It has been suggested that category-specific recognition disorders for natural objects may reflect that natural objects are more structurally (visually) similar than artefacts and therefore more difficult to recognize following brain damage. On this account one might expect a positive relationship between blood flow and structural similarity in areas involved in visual object recognition. Contrary to this expectation we report a negative relationship in that identification of articles of clothing cause more extensive activation than identification of vegetables/fruit and animals even though items from the categories of animals and vegetables/fruit are rated as more structurally similar than items from the category of articles of clothing. Given that this pattern cannot be explained in terms of a tradeoff between activation and accuracy, we interpret these findings within a model where the matching of visual forms to memory incorporates two operations: (i) the integration of stored object features into whole object representations (integral units), and (ii) the competition between activated integral units for selection (i.e. identification). In addition, we suggest that these operations are differentially affected by structural similarity in that high structural similarity may be beneficial for the integration of stored features into integral units, thus explaining the greater activation found with articles of clothing, whereas it may be harmful for the selection process proper because a greater range of candidate integral units will be activated and compete for selection, thus explaining the higher error rate associated with animals. We evaluate the model based on previous evidence from both normal subjects and patients with category-specific disorders and argue that this model can help reconcile otherwise conflicting data.

The Heterogeneity of Category-Specific Semantic Disorders: Evidence from a New Case

We report a new case of category-specific semantic impairment, affecting living entities, in a patient with traumatic brain damage. In the present investigation we attempted to replicate as closely as possible the testing procedures which have been developed by Caramazza and Shelton (1998) to evaluate EW, a patient with a selective semantic disorder for the animal category. The results in our patient indicated a different performance profile, characterised by a more extensive semantic disorder for living entities, and by a more severe loss of specific visual rather than functional knowledge. These findings concur with other evidence indicating that category-specific semantic disorders are heterogeneous, reflecting different mechanisms of impairment, most likely associated with different neurobiological underpinnings.

Abstracts of the Inaugural Australian Conference for Cognitive Neuropsychology and Cognitive Neuropsychiatry

The first Australian Conference for Cognitive Neuropsychology and Cognitive Neuropsychiatry was conducted by the School of Psychology at Deakin University, Geelong, from Friday, July 13 to Sunday, July 15 and was attended by over 50 cognitive psychologists, neuropsychologists and speech pathologists from Australia, New Zealand, Singapore and the UK. The Conference aimed to bring together researchers from different disciplines including linguistics, psychology, philosophy and speech pathology to present research that relates (neuropsychological or psychiatric) impairment to theories of normal cognitive functioning. The scientific program of the conference included 24 papers of exceptional quality. They were organised into the following thematic sessions: Disorders of language comprehension and production; Semantic memory and category-specific disorders; Reading: development and acquired dyslexia; Writing: development and acquired dyslexia; Memory; Object and face recognition; Theory of mind; Misidentification syndromes. Keynote speakers were Professor Andy Young from the University of York, England and Professor Max Coltheart from the Macquarie Centre for Cognitive Sciences, Sydney.

Category-Specific Naming Errors in Normal Subjects: The Influence of Evolution and Experience

The importance of “artifactual” variables (such as conceptual familiarity) have been highlighted in current accounts of category-specific disorders for living things (e.g., Funnell & Sheridan, 1992). The difficulties experienced by patients are essentially viewed as an exaggeration of normal processes and the implication is that normal subjects should also have greater difficulty naming living items (because they have lower conceptual familiarity than nonliving things). The current study examined normal subjects' ability to name pictures of artifact-matched sets of living and nonliving things in a naming-to-deadline paradigm. Contrary to the prediction, normal subjects made more nonliving naming errors. Furthermore, female subjects made more nonliving-thing errors than male subjects. These findings could not be reduced to differences in either category-based or gender-based familiarity ratings. Rather, it is proposed that an elaborated domain-specific evolutionary model parsimoniously explains both the greater incidence of living thing deficits in patients and the better performance of normal subjects with living things.

What the Locus of Brain Lesion Tells us About the Nature of the Cognitive Defect Underlying Category-Specific Disorders: A Review

Different models have been proposed to account for the nature of the cognitive defects underlying category-specific disorders for living and non-living things. One model assumes that the living/non-living distinction is the by-product of a more basic dichotomy, contingent upon the different weighting that visuo-perceptual and functional attributes have in the identification of members of these categories. A second model submits that evolutionary pressure resulted in the elaboration of dedicated neural mechanisms for the domains of living (animals and plants) and non-living (artefacts) things. A third model proposes that the different level of interconnections existing between perceptual and functional features in living and non living things may be more important than the weighting of these features. Each of these models makes implicit assumptions about the extent and the localization of brain lesions provoking category-specific disorders. However, it must also be considered that these disorders are heterogeneous in nature, resulting from defects located at the semantic, lexical or visual level. In the present review of the literature, we kept this distinction in mind in trying to analyze the neuroanatomical correlates of living and nonliving disorders. Our findings showed that there is a correlation between the locus of lesion and the patterns of categorical impairment: (a) a bilateral injury to the antero-mesial and inferior parts of the temporal lobes was found in patients with a category-specific semantic impairment for living things; (b) a lesion of the infero-mesial parts of the temporo-occipital areas of the left hemisphere was found in a group of patients showing a specific lexical impairment for members of the ‘plants’ category; (c) an extensive lesion of the areas lying on the dorso-lateral convexity of the left hemisphere was found in patients with a category-specific semantic impairment for man-made artefacts. Taken together, these results seem to show that the category-specific disorder is crucially related to the kind of semantic information processed by the damaged areas.