Concepts and categories: a cognitive neuropsychological perspective

Shapes, scents and sounds: quantifying the full multi-sensory basis of conceptual knowledge

Contemporary neuroscience theories assume that concepts are formed through experience in multiple sensory-motor modalities. Quantifying the contribution of each modality to different object categories is critical to understanding the structure of the conceptual system and to explaining category-specific knowledge deficits. Verbal feature listing is typically used to elicit this information but has a number of drawbacks: sensory knowledge often cannot easily be translated into verbal features and many features are experienced in multiple modalities. Here, we employed a more direct approach in which subjects rated their knowledge of objects in each sensory-motor modality separately. Compared with these ratings, feature listing over-estimated the importance of visual form and functional knowledge and under-estimated the contributions of other sensory channels. An item's sensory rating proved to be a better predictor of lexical-semantic processing speed than the number of features it possessed, suggesting that ratings better capture the overall quantity of sensory information associated with a concept. Finally, the richer, multi-modal rating data not only replicated the sensory-functional distinction between animals and non-living things but also revealed novel distinctions between different types of artefact. Hierarchical cluster analyses indicated that mechanical devices (e.g., vehicles) were distinct from other non-living objects because they had strong sound and motion characteristics, making them more similar to animals in this respect. Taken together, the ratings align with neuroscience evidence in suggesting that a number of distinct sensory processing channels make important contributions to object knowledge. Multi-modal ratings for 160 objects are provided as supplementary materials.

Electrophysiological studies of face processing in developmental prosopagnosia: neuropsychological and neurodevelopmental perspectives

People with developmental prosopagnosia (DP) show severe face-recognition deficits that typically emerge during childhood without history of neurological damage. We review findings from recent event-related brain potential (ERP) studies of face perception and face recognition in DP. The generic face-sensitivity of the N170 component is present in most DPs, suggesting rapid category-selective streaming of facial information. In contrast, DPs show atypical N170 face inversion effects, indicative of impaired structural encoding, specifically for upright faces. In line with neurodevelopmental accounts of DP, these effects are similar to those observed for other developmental disorders, as well as for younger children and older adults. Identity-sensitive ERP components (N250, P600f) triggered during successful face recognition are similar for DPs and control participants, indicating that the same mechanisms are active in both groups. The presence of covert face-recognition effects for the N250 component suggests that visual face memory and semantic memory can become disconnected in some individuals with DP. The implications of these results for neuropsychological and neurodevelopmental perspectives on DP are discussed.

Physical experience leads to enhanced object perception in parietal cortex: insights from knot tying

What does it mean to "know" what an object is? Viewing objects from different categories (e.g., tools vs. animals) engages distinct brain regions, but it is unclear whether these differences reflect object categories themselves or the tendency to interact differently with objects from different categories (grasping tools, not animals). Here we test how the brain constructs representations of objects that one learns to name or physically manipulate. Participants learned to name or tie different knots and brain activity was measured whilst performing a perceptual discrimination task with these knots before and after training. Activation in anterior intraparietal sulcus, a region involved in object manipulation, was specifically engaged when participants viewed knots they learned to tie. This suggests that object knowledge is linked to sensorimotor experience and its associated neural systems for object manipulation. Findings are consistent with a theory of embodiment in which there can be clear overlap in brain systems that support conceptual knowledge and control of object manipulation.

Conceptual representations of perceptual knowledge

Many neuroimaging studies of semantic memory have argued that knowledge of an object's perceptual properties are represented in a modality-specific manner. These studies often base their argument on finding activation in the left-hemisphere fusiform gyrus-a region assumed to be involved in perceptual processing-when the participant is verifying verbal statements about objects and properties. In this paper, we report an extension of one of these influential papers-Kan, Barsalou, Solomon, Minor, and Thompson-Schill (2003 )-and present evidence for an amodal component in the representation and processing of perceptual knowledge. Participants were required to verify object-property statements (e.g., "cat-whiskers?"; "bear-wings?") while they were being scanned by functional magnetic resonance imaging (fMRI). We replicated Kan et al.'s activation in the left fusiform gyrus, but also found activation in regions of left inferior frontal gyrus (IFG) and middle-temporal gyrus, areas known to reflect amodal processes or representations. Further, only activations in the left IFG, an amodal area, were correlated with measures of behavioural performance.

Electrophysiological potentials reveal cortical mechanisms for mental imagery, mental simulation, and grounded (embodied) cognition

Grounded cognition theory proposes that cognition, including meaning, is grounded in sensorimotor processing. The mechanism for grounding cognition is mental simulation, which is a type of mental imagery that re-enacts modal processing. To reveal top-down, cortical mechanisms for mental simulation of shape, event-related potentials were recorded to face and object pictures preceded by mental imagery. Mental imagery of the identical face or object picture (congruous condition) facilitated not only categorical perception (VPP/N170) but also later visual knowledge [N3(00) complex] and linguistic knowledge (N400) for faces more than objects, and strategic semantic analysis (late positive complex) between 200 and 700 ms. The later effects resembled semantic congruity effects with pictures. Mental imagery also facilitated category decisions, as a P3 peaked earlier for congruous than incongruous (other category) pictures, resembling the case when identical pictures repeat immediately. Thus mental imagery mimics semantic congruity and immediate repetition priming processes with pictures. Perception control results showed the opposite for faces and were in the same direction for objects: Perceptual repetition adapts (and so impairs) processing of perceived faces from categorical perception onward, but primes processing of objects during categorical perception, visual knowledge processes, and strategic semantic analysis. For both imagery and perception, differences between faces and objects support domain-specificity and indicate that cognition is grounded in modal processing. Altogether, this direct neural evidence reveals that top-down processes of mental imagery sustain an imagistic representation that mimics perception well enough to prime subsequent perception and cognition. Findings also suggest that automatic mental simulation of the visual shape of faces and objects operates between 200 and 400 ms, and strategic mental simulation operates between 400 and 700 ms.

The very same thing: Extending the object token concept to incorporate causal constraints on individual identity

The contributions of feature recognition, object categorization, and recollection of episodic memories to the re-identification of a perceived object as the very same thing encountered in a previous perceptual episode are well understood in terms of both cognitive-behavioral phenomenology and neurofunctional implementation. Human beings do not, however, rely solely on features and context to re-identify individuals; in the presence of featural change and similarly-featured distractors, people routinely employ causal constraints to establish object identities. Based on available cognitive and neurofunctional data, the standard object-token based model of individual re-identification is extended to incorporate the construction of unobserved and hence fictive causal histories (FCHs) of observed objects by the pre-motor action planning system. It is suggested that functional deficits in the construction of FCHs are associated with clinical outcomes in both autism spectrum disorders and later-stage stage Alzheimer’s disease.

Gray matter density of auditory association cortex relates to knowledge of sound concepts in primary progressive aphasia

Long-term memory integrates the multimodal information acquired through perception into unified concepts, supporting object recognition, thought, and language. While some theories of human cognition have considered concepts to be abstract symbols, recent functional neuroimaging evidence has supported an alternative theory: that concepts are multimodal representations associated with the sensory and motor systems through which they are acquired. However, few studies have examined the effects of cortical lesions on the sensory and motor associations of concepts. We tested the hypothesis that individuals with disease in auditory association cortex would have difficulty processing concepts with strong sound associations (e.g., thunder). Human participants with the logopenic variant of primary progressive aphasia (lvPPA) performed a recognition task on words with strong associations in three modalities: Sound, Sight, and Manipulation. LvPPA participants had selective difficulty on Sound words relative to other modalities. Structural MRI analysis in lvPPA revealed gray matter atrophy in auditory association cortex, as defined functionally in a separate BOLD fMRI study of healthy adults. Moreover, lvPPA showed reduced gray matter density in the region of auditory association cortex that healthy participants activated when processing the same Sound words in a separate BOLD fMRI experiment. Finally, reduced gray matter density in this region in lvPPA directly correlated with impaired performance on Sound words. These findings support the hypothesis that conceptual memories are represented in the sensory and motor association cortices through which they are acquired.

Automated semantic indices related to cognitive function and rate of cognitive decline

The objective of our study is to introduce a fully automated, computational linguistic technique to quantify semantic relations between words generated on a standard semantic verbal fluency test and to determine its cognitive and clinical correlates. Cognitive differences between patients with Alzheimer's disease and mild cognitive impairment are evident in their performance on the semantic verbal fluency test. In addition to the semantic verbal fluency test score, several other performance characteristics sensitive to disease status and predictive of future cognitive decline have been defined in terms of words generated from semantically related categories (clustering) and shifting between categories (switching). However, the traditional assessment of clustering and switching has been performed manually in a qualitative fashion resulting in subjective scoring with limited reproducibility and scalability. Our approach uses word definitions and hierarchical relations between the words in WordNet(®), a large electronic lexical database, to quantify the degree of semantic similarity and relatedness between words. We investigated the novel semantic fluency indices of mean cumulative similarity and relatedness between all pairs of words regardless of their order, and mean sequential similarity and relatedness between pairs of adjacent words in a sample of patients with clinically diagnosed probable (n=55) or possible (n=27) Alzheimer's disease or mild cognitive impairment (n=31). The semantic fluency indices differed significantly between the diagnostic groups, and were strongly associated with neuropsychological tests of executive function, as well as the rate of global cognitive decline. Our results suggest that word meanings and relations between words shared across individuals and computationally modeled via WordNet and large text corpora provide the necessary context to account for the variability in language-based behavior and relate it to cognitive dysfunction observed in mild cognitive impairment and Alzheimer's disease.

Tracking neural coding of perceptual and semantic features of concrete nouns

We present a methodological approach employing magnetoencephalography (MEG) and machine learning techniques to investigate the flow of perceptual and semantic information decodable from neural activity in the half second during which the brain comprehends the meaning of a concrete noun. Important information about the cortical location of neural activity related to the representation of nouns in the human brain has been revealed by past studies using fMRI. However, the temporal sequence of processing from sensory input to concept comprehension remains unclear, in part because of the poor time resolution provided by fMRI. In this study, subjects answered 20 questions (e.g. is it alive?) about the properties of 60 different nouns prompted by simultaneous presentation of a pictured item and its written name. Our results show that the neural activity observed with MEG encodes a variety of perceptual and semantic features of stimuli at different times relative to stimulus onset, and in different cortical locations. By decoding these features, our MEG-based classifier was able to reliably distinguish between two different concrete nouns that it had never seen before. The results demonstrate that there are clear differences between the time course of the magnitude of MEG activity and that of decodable semantic information. Perceptual features were decoded from MEG activity earlier in time than semantic features, and features related to animacy, size, and manipulability were decoded consistently across subjects. We also observed that regions commonly associated with semantic processing in the fMRI literature may not show high decoding results in MEG. We believe that this type of approach and the accompanying machine learning methods can form the basis for further modeling of the flow of neural information during language processing and a variety of other cognitive processes.

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).

Neural dynamics of animacy processing in language comprehension: ERP evidence from the interpretation of classifier-noun combinations

An event-related potential experiment was conducted to investigate the temporal neural dynamics of animacy processing in the interpretation of classifier-noun combinations. Participants read sentences that had a non-canonical structure, object noun +subject noun+verb+numeral-classifier+adjective. The object noun and its classifier were either (a) congruent, (b) incongruent, but matching in animacy, or (c) incongruent, mismatching in animacy. An N400 effect was observed for both incongruent conditions, but not for additional mismatch in animacy. When only data from participants who accepted the non-canonical structure were analyzed, the animacy mismatch elicited a P600 but still no N400. These findings suggest that animacy information is not used immediately for semantic integration of nouns and their classifiers, but is used in a later analysis reflected by P600. Thus, the temporal neural dynamics of animacy processing in sentence comprehension may be modulated by the relevance of animacy to thematic interpretation.

Motion as manipulation: implementation of force-motion analogies by event-file binding and action planning

Tool-improvisation analogies are structure-mapping inferences implemented, in many species, by event-file binding and pre-motor action planning. These processes act on multi-modal representations of currently perceived situations and eventuate in motor acts that can be directly evaluated for success or failure; they employ implicit representations of force-motion relations encoded by the pre-motor system and do not depend on explicit, language-like representations of relational concepts. A detailed reconstruction of the analogical reasoning steps involved in Rutherford's and Bohr's development of the first quantized-orbit model of atomic structure is used to show that human force-motion analogies can in general be implemented by these mechanisms. This event-file manipulation model of the implementation of force-motion analogies is distinguished from the standard view that structure-mapping analogies require the manipulation of explicit, language-like representations of relational concepts.

Losing the sound of concepts: damage to auditory association cortex impairs the processing of sound-related concepts

Conceptual knowledge is classically supposed to be abstract and represented in an amodal unitary system, distinct from the sensory and motor brain systems. A more recent embodiment view of conceptual knowledge, however, proposes that concepts are grounded in distributed modality-specific brain areas which typically process sensory or action-related object information. Recent neuroimaging evidence suggested the significance of left auditory association cortex encompassing posterior superior and middle temporal gyrus in coding conceptual sound features of everyday objects. However, a causal role of this region in processing conceptual sound information has yet to be established. Here we had the unique chance to investigate a patient, JR, with a focal lesion in left posterior superior and middle temporal gyrus. To test the necessity of this region in conceptual and perceptual processing of sound information we administered four different experimental tasks to JR: Visual word recognition, category fluency, sound recognition and voice classification. Compared with a matched control group, patient JR was consistently impaired in conceptual processing of sound-related everyday objects (e.g., "bell"), while performance for non-sound-related everyday objects (e.g., "armchair"), animals, whether they typically produce sounds (e.g., "frog") or not (e.g., "tortoise"), and musical instruments (e.g., "guitar") was intact. An analogous deficit pattern in JR was also obtained for perceptual recognition of the corresponding sounds. Hence, damage to left auditory association cortex specifically impairs perceptual and conceptual processing of sounds from everyday objects. In support of modality-specific theories, these findings strongly evidence the necessity of auditory association cortex in coding sound-related conceptual information.

First-pass selectivity for semantic categories in human anteroventral temporal lobe

How the brain encodes the semantic concepts represented by words is a fundamental question in cognitive neuroscience. Hemodynamic neuroimaging studies have robustly shown that different areas of posteroventral temporal lobe are selectively activated by images of animals versus manmade objects. Selective responses in these areas to words representing animals versus objects are sometimes also seen, but they are task-dependent, suggesting that posteroventral temporal cortex may encode visual categories, while more anterior areas encode semantic categories. Here, using the spatiotemporal resolution provided by intracranial macroelectrode and microelectrode arrays, we report category-selective responses to words representing animals and objects in human anteroventral temporal areas including inferotemporal, perirhinal, and entorhinal cortices. This selectivity generalizes across tasks and sensory modalities, suggesting that it represents abstract lexicosemantic categories. Significant category-specific responses are found in measures sensitive to synaptic activity (local field potentials, high gamma power, current sources and sinks) and unit-firing (multiunit and single-unit activity). Category-selective responses can occur at short latency (as early as 130 ms) in middle cortical layers and thus are extracted in the first pass of activity through the anteroventral temporal lobe. This activation may provide input to posterior areas for iconic representations when required by the task, as well as to the hippocampal formation for categorical encoding and retrieval of memories, and to the amygdala for emotional associations. More generally, these results support models in which the anteroventral temporal lobe plays a primary role in the semantic representation of words.

Folkbiology

Recent work in cognitive science suggests that children have framework theories unique to specific domains such as physics, psychology, and biology that provide causal explanations and support predictions about phenomena within them. They further guide how children develop the later theories of adults, both formal and informal. In this article, we focus on a particular framework or naïve theory, folkbiology, and review debates concerning how it ought best to be characterized, its origins and developmental course, whether aspects of it can be said to be universal to people in all cultural settings, how it informs our understanding of the brain, and what implications it has for science education. In so doing, we discuss how the cognitive scientific study of folkbiology takes us across disciplinary bounds into related work in the philosophy of science, cultural anthropology, neuropsychology, and education. WIREs Cogn Sci 2012, 3:105-115. doi: 10.1002/wcs.150 For further resources related to this article, please visit the WIREs website.

A common, high-dimensional model of the representational space in human ventral temporal cortex

We present a high-dimensional model of the representational space in human ventral temporal (VT) cortex in which dimensions are response-tuning functions that are common across individuals and patterns of response are modeled as weighted sums of basis patterns associated with these response tunings. We map response-pattern vectors, measured with fMRI, from individual subjects' voxel spaces into this common model space using a new method, "hyperalignment." Hyperalignment parameters based on responses during one experiment--movie viewing--identified 35 common response-tuning functions that captured fine-grained distinctions among a wide range of stimuli in the movie and in two category perception experiments. Between-subject classification (BSC, multivariate pattern classification based on other subjects' data) of response-pattern vectors in common model space greatly exceeded BSC of anatomically aligned responses and matched within-subject classification. Results indicate that population codes for complex visual stimuli in VT cortex are based on response-tuning functions that are common across individuals.

Closely overlapping responses to tools and hands in left lateral occipitotemporal cortex

The perception of object-directed actions performed by either hands or tools recruits regions in left fronto-parietal cortex. Here, using functional MRI (fMRI), we tested whether the common role of hands and tools in object manipulation is also reflected in the distribution of response patterns to these categories in visual cortex. In two experiments we found that static pictures of hands and tools activated closely overlapping regions in left lateral occipitotemporal cortex (LOTC). Left LOTC responses to tools selectively overlapped with responses to hands but not with responses to whole bodies, nonhand body parts, other objects, or visual motion. Multivoxel pattern analysis in left LOTC indicated a high degree of similarity between response patterns to hands and tools but not between hands or tools and other body parts. Finally, functional connectivity analysis showed that the left LOTC hand/tool region was selectively connected, relative to neighboring body-, motion-, and object-responsive regions, with regions in left intraparietal sulcus and left premotor cortex that have previously been implicated in hand/tool action-related processing. Taken together, these results suggest that action-related object properties shared by hands and tools are reflected in the organization of high-order visual cortex. We propose that the functional organization of high-order visual cortex partly reflects the organization of downstream functional networks, such as the fronto-parietal action network, due to differences within visual cortex in the connectivity to these networks.

Relationship between functional magnetic resonance imaging-identified regions and neuronal category selectivity

Functional magnetic resonance imaging (fMRI) has been used extensively to identify regions in the inferior temporal (IT) cortex that are selective for categories of visual stimuli. However, comparatively little is known about the neuronal responses relative to these fMRI-defined regions. Here, we compared in nonhuman primates the distribution and response properties of IT neurons recorded within versus outside fMRI regions selective for four different visual categories: faces, body parts, objects, and places. Although individual neurons that preferred each of the four categories were found throughout the sampled regions, they were most concentrated within the corresponding fMRI region, decreasing significantly within 1-4 mm from the edge of these regions. Furthermore, the correspondence between fMRI and neuronal distributions was specific to neurons that increased their firing rates in response to the visual stimuli but not to neurons suppressed by visual stimuli, suggesting that the processes associated with inhibiting neuronal activity did not contribute strongly to the fMRI signal in this experiment.

Conceptual structure: Towards an integrated neuro-cognitive account

How are the meanings of concepts represented and processed? We present a cognitive model of conceptual representations and processing - the Conceptual Structure Account (CSA; Tyler & Moss, 2001) - as an example of a distributed, feature-based approach. In a first section, we describe the CSA and evaluate relevant neuropsychological and experimental behavioral data. We discuss studies using linguistic and non-linguistic stimuli, which are both presumed to access the same conceptual system. We then take the CSA as a framework for hypothesising how conceptual knowledge is represented and processed in the brain. This neuro-cognitive approach attempts to integrate the distributed feature-based characteristics of the CSA with a distributed and feature-based model of sensory object processing. Based on a review of relevant functional imaging and neuropsychological data, we argue that distributed accounts of feature-based representations have considerable explanatory power, and that a cognitive model of conceptual representations is needed to understand their neural bases.

Neural Basis of Linearization in Speech Production

An initial stage of speech production is conceptual planning, where a speaker determines which information to convey first (the linearization problem). This fMRI study investigated the linearization process during the production of “before” and “after” sentences. In “after” sentences, a series of events is expressed in the order of event occurrence. In “before” sentences, however, the order of event mention is achieved by reversing the chronological order. We suggested that the linearization process may be supported by a neural network connecting the left middle temporal gyrus (MTG) with the medial superior frontal gyrus, left middle frontal gyrus, and left angular gyrus/inferior parietal gyrus. Within this network, regions were more activated and interregional interactions were strongly enhanced for producing “before” than “after” sentences. The left MTG was also functionally connected with the left orbital inferior frontal gyrus, contributing to the retrieval of necessary world knowledge and linguistic knowledge. Connectivity between these two regions was not different between conditions.

Motor knowledge is one dimension for concept organization: further evidence from a Chinese semantic dementia case

Neuropsychological and neuroimaging studies have indicated that motor knowledge is one potential dimension along which concepts are organized. Here we present further direct evidence for the effects of motor knowledge in accounting for categorical patterns across object domains (living vs. nonliving) and grammatical domains (nouns vs. verbs), as well as the integrity of other modality-specific knowledge (e.g., visual). We present a Chinese case, XRK, who suffered from semantic dementia with left temporal lobe atrophy. In naming and comprehension tasks, he performed better at nonliving items than at living items, and better at verbs than at nouns. Critically, multiple regression method revealed that these two categorical effects could be both accounted for by the charade rating, a continuous measurement of the significance of motor knowledge for a concept or a semantic feature. Furthermore, charade rating also predicted his performances on the generation frequency of semantic features of various modalities. These findings consolidate the significance of motor knowledge in conceptual organization and further highlights the interactions between different types of semantic knowledge.

Expertise modulates the neural basis of context dependent recognition of objects and their relations

Recognition of objects and their relations is necessary for orienting in real life. We examined cognitive processes related to recognition of objects, their relations, and the patterns they form by using the game of chess. Chess enables us to compare experts with novices and thus gain insight in the nature of development of recognition skills. Eye movement recordings showed that experts were generally faster than novices on a task that required enumeration of relations between chess objects because their extensive knowledge enabled them to immediately focus on the objects of interest. The advantage was less pronounced on random positions where the location of chess objects, and thus typical relations between them, was randomized. Neuroimaging data related experts' superior performance to the areas along the dorsal stream-bilateral posterior temporal areas and left inferior parietal lobe were related to recognition of object and their functions. The bilateral collateral sulci, together with bilateral retrosplenial cortex, were also more sensitive to normal than random positions among experts indicating their involvement in pattern recognition. The pattern of activations suggests experts engage the same regions as novices, but also that they employ novel additional regions. Expert processing, as the final stage of development, is qualitatively different than novice processing, which can be viewed as the starting stage. Since we are all experts in real life and dealing with meaningful stimuli in typical contexts, our results underline the importance of expert-like cognitive processing on generalization of laboratory results to everyday life.

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.

Decoding patterns of human brain activity

Considerable information about mental states can be decoded from noninvasive measures of human brain activity. Analyses of brain activity patterns can reveal what a person is seeing, perceiving, attending to, or remembering. Moreover, multidimensional models can be used to investigate how the brain encodes complex visual scenes or abstract semantic information. Such feats of "brain reading" or "mind reading," though impressive, raise important conceptual, methodological, and ethical issues. What does successful decoding reveal about the cognitive functions performed by a brain region? How should brain signals be spatially selected and mathematically combined to ensure that decoding reflects inherent computations of the brain rather than those performed by the decoder? We highlight recent advances and describe how multivoxel pattern analysis can provide a window into mind-brain relationships with unprecedented specificity, when carefully applied. However, as brain-reading technology advances, issues of neuroethics and mental privacy will be important to consider.

Modeling abnormal priming in Alzheimer's patients with a free association network

Alzheimer's Disease irremediably alters the proficiency of word search and retrieval processes even at its early stages. Such disruption can sometimes be paradoxical in specific language tasks, for example semantic priming. Here we focus in the striking side-effect of hyperpriming in Alzheimer's Disease patients, which has been well-established in the literature for a long time. Previous studies have evidenced that modern network theory can become a powerful complementary tool to gain insight in cognitive phenomena. Here, we first show that network modeling is an appropriate approach to account for semantic priming in normal subjects. Then we turn to priming in degraded cognition: hyperpriming can be readily understood in the scope of a progressive degradation of the semantic network structure. We compare our simulation results with previous empirical observations in diseased patients finding a qualitative agreement. The network approach presented here can be used to accommodate current theories about impaired cognition, and towards a better understanding of lexical organization in healthy and diseased patients.

Semantic category effects modulate visual priming in neglect patients

Previous studies indicate that extinguished stimuli can still be unconsciously processed, leading to implicit priming effects. Here we investigated whether these implicit effects might be modulated by the semantic nature of the stimuli. Five neglect patients and ten controls performed an identification task of items belonging to living and non-living categories. In the study phase photographs of animals and artifacts were presented either to the left visual field (LVF) or to the right visual field (RVF). In the identification phase, each stimulus was displayed centrally and was revealed in a sequence of frames where the item was represented by an increasingly less and less filtered image up to a complete version. The results showed that lateralized stimuli differentially affected controls' and neglect patients' memory retrieval. In controls memory traces from the study phase served as efficient primes, thereby reducing the amount of information necessary for the identification of both stimulus categories. Moreover, hemispheric differences emerged with an advantage of the RVF/left hemisphere for artifact items, while no difference was found for living things. Neglect patients showed a priming effect for artifact items presented either to the RVF/left hemisphere or LVF/right hemisphere, as well as for living items presented to the RVF/left hemisphere, but not for living items presented to the LVF/right hemisphere. The priming effect observed for extinguished artifacts is consistent with the evidence of the existence of a specific mechanism destined to analyze, in an automatic and implicit fashion, motor-relevant information of manipulable objects and tools, which are important for identification process. Results are discussed in relation to current models of organization of conceptual knowledge within the framework of different processes performed by the two hemispheres.

What drives the organization of object knowledge in the brain?

Various forms of category-specificity have been described at both the cognitive and neural levels, inviting the inference that different semantic domains are processed by distinct, dedicated mechanisms. In this paper, we argue for an extension of a domain-specific interpretation to these phenomena that is based on network-level analyses of functional coupling among brain regions. On this view, domain-specificity in one region of the brain emerges because of innate connectivity with a network of regions that also process information about that domain. Recent findings are reviewed that converge with this framework, and a new direction is outlined for understanding the neural principles that shape the organization of conceptual knowledge.

Flexibility in embodied language understanding

Do people use sensori-motor cortices to understand language? Here we review neurocognitive studies of language comprehension in healthy adults and evaluate their possible contributions to theories of language in the brain. We start by sketching the minimal predictions that an embodied theory of language understanding makes for empirical research, and then survey studies that have been offered as evidence for embodied semantic representations. We explore four debated issues: first, does activation of sensori-motor cortices during action language understanding imply that action semantics relies on mirror neurons? Second, what is the evidence that activity in sensori-motor cortices plays a functional role in understanding language? Third, to what extent do responses in perceptual and motor areas depend on the linguistic and extra-linguistic context? And finally, can embodied theories accommodate language about abstract concepts? Based on the available evidence, we conclude that sensori-motor cortices are activated during a variety of language comprehension tasks, for both concrete and abstract language. Yet, this activity depends on the context in which perception and action words are encountered. Although modality-specific cortical activity is not a sine qua non of language processing even for language about perception and action, sensori-motor regions of the brain appear to make functional contributions to the construction of meaning, and should therefore be incorporated into models of the neurocognitive architecture of language.

Emotional speech processing: disentangling the effects of prosody and semantic cues

To inform how emotions in speech are implicitly processed and registered in memory, we compared how emotional prosody, emotional semantics, and both cues in tandem prime decisions about conjoined emotional faces. Fifty-two participants rendered facial affect decisions (Pell, 2005a), indicating whether a target face represented an emotion (happiness or sadness) or not (a facial grimace), after passively listening to happy, sad, or neutral prime utterances. Emotional information from primes was conveyed by: (1) prosody only; (2) semantic cues only; or (3) combined prosody and semantic cues. Results indicated that prosody, semantics, and combined prosody-semantic cues facilitate emotional decisions about target faces in an emotion-congruent manner. However, the magnitude of priming did not vary across tasks. Our findings highlight that emotional meanings of prosody and semantic cues are systematically registered during speech processing, but with similar effects on associative knowledge about emotions, which is presumably shared by prosody, semantics, and faces.

A domain-specific system for representing knowledge of both man-made objects and human actions. Evidence from a case with an association of deficits

We report the single-case study of a brain-damaged individual, JJG, presenting with a conceptual deficit and whose knowledge of living things, man-made objects, and actions was assessed. The aim was to seek for empirical evidence pertaining to the issue of how conceptual knowledge of objects, both living things and man-made objects, is related to conceptual knowledge of actions at the functional level. We first found that JJG's conceptual knowledge of both man-made objects and actions was similarly impaired while his conceptual knowledge of living things was spared as well as his knowledge of unique entities. We then examined whether this pattern of association of a conceptual deficit for both man-made objects and actions could be accounted for, first, by the "sensory/functional" and, second, the "manipulability" account for category-specific conceptual impairments advocated within the Feature-Based-Organization theory of conceptual knowledge organization, by assessing, first, patient's knowledge of sensory compared to functional features, second, his knowledge of manipulation compared to functional features and, third, his knowledge of manipulable compared to non-manipulable objects and actions. The later assessment also allowed us to evaluate an account for the deficits in terms of failures of simulating the hand movements implied by manipulable objects and manual actions. The findings showed that, contrary to the predictions made by the "sensory/functional", the "manipulability", and the "failure-of-simulating" accounts for category-specific conceptual impairments, the patient's association of deficits for both man-made objects and actions was not associated with a disproportionate impairment of functional compared to sensory knowledge or of manipulation compared to functional knowledge; manipulable items were not more impaired than non-manipulable items either. In the general discussion, we propose to account for the patient's association of deficits by the hypothesis that concepts whose core property is that of being a mean of achieving a goal - like the concepts of man-made objects and of actions - are learned, represented and processed by a common domain-specific conceptual system, which would have evolved to allow human beings to quickly and efficiently design and understand means to achieve goals and purposes.

Neuroplasticity of semantic representations for musical instruments in professional musicians

Professional musicians constitute a model par excellence for understanding experience-dependent plasticity in the human brain, particularly in the auditory domain. Their intensive sensorimotor experience with musical instruments has been shown to entail plastic brain alterations in cortical perceptual and motor maps. It remains an important question whether this neuroplasticity might extend beyond basic perceptual and motor functions and even shape higher-level conceptualizations by which we conceive our physical and social world. Here we show using functional magnetic resonance imaging (fMRI) that conceptual processing of visually presented musical instruments activates auditory association cortex encompassing right posterior superior temporal gyrus, as well as adjacent areas in the superior temporal sulcus and the upper part of middle temporal gyrus (pSTG/MTG) only in musicians, but not in musical laypersons. These areas in and adjacent to auditory association cortex were not only recruited by conceptual processing of musical instruments during visual object recognition, but also by auditory perception of real sounds. Hence, the unique intensive experience of musicians with musical instruments establishes a link between auditory perceptual and conceptual brain systems. Experience-driven neuroplasticity in musicians is thus not confined to alterations of perceptual and motor maps, but even leads to the establishment of higher-level semantic representations for musical instruments in and adjacent to auditory association cortex. These findings highlight the eminent importance of sensory and motor experience for acquiring rich concepts.

Category learning in the brain

The ability to group items and events into functional categories is a fundamental characteristic of sophisticated thought. It is subserved by plasticity in many neural systems, including neocortical regions (sensory, prefrontal, parietal, and motor cortex), the medial temporal lobe, the basal ganglia, and midbrain dopaminergic systems. These systems interact during category learning. Corticostriatal loops may mediate recursive, bootstrapping interactions between fast reward-gated plasticity in the basal ganglia and slow reward-shaded plasticity in the cortex. This can provide a balance between acquisition of details of experiences and generalization across them. Interactions between the corticostriatal loops can integrate perceptual, response, and feedback-related aspects of the task and mediate the shift from novice to skilled performance. The basal ganglia and medial temporal lobe interact competitively or cooperatively, depending on the demands of the learning task.