& Experiments investigating the mechanisms involved in visual processing often fail to separate low-level encoding mechanisms from higher-level behaviorally relevant ones. Using an alternating dual-task event-related potential (ERP) experimental paradigm (animals or vehicles categorization) where targets of one task are intermixed among distractors of the other, we show that visual categorization of a natural scene involves different mechanisms with different time courses: a perceptual, task-independent mechanism, followed by a taskrelated, category-independent process. Although average ERP responses reflect the visual category of the stimulus shortly after visual processing has begun (e.g. 75±80 msec), this difference is not correlated with the subject's behavior until 150 msec poststimulus. &

Here we review recent findings that reveal the functional properties of extra-striate regions in the human visual cortex that are involved in the representation and perception of objects. We characterize both the invariant and non-invariant properties of these regions and we discuss the correlation between activation of these regions and recognition. Overall, these results indicate that the lateral occipital complex plays an important role in human object recognition.

INTRODUCTION How do we go from seeing a word to accessing its meaning? Classical models of word processing postulate that words are initially recognized in modalityspecific input lexicons before contacting a common semantic representation (Caramazza, 1996; Morton, 1979). This predicts that areas which are engaged in semantic-level processing should activate in direct correlation with the amount of semantic manipulation required by the task and do so independent of the modality of presentation of the concept (Chao et al., 2000; Perani et al., 1999; Vandenberghe et al., 1996). Here, we attempt to identify the cerebral areas engaged in the coding and internal manipulation of an abstract semantic content, the meaning of number words. Although numbers can be written in multiple notations, such as words or digits, the parietal lobes are thought to comprise a notation-independent representation of their semantic content as quantities. According to the "triple-code model" of number process

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

The authors identify 2 major types of statistical data from which semantic representations can be learned. These are denoted as experiential data and distributional data. Experiential data are derived by way of experience with the physical world and comprise the sensory-motor data obtained through sense receptors. Distributional data, by contrast, describe the statistical distribution of words across spoken and written language. The authors claim that experiential and distributional data represent distinct data types and that each is a nontrivial source of semantic information. Their theoretical proposal is that human semantic representations are derived from an optimal statistical combination of these 2 data types. Using a Bayesian probabilistic model, they demonstrate how word meanings can be learned by treating experiential and distributional data as a single joint distribution and learning the statistical structure that underlies it. The semantic representations that are learned in this manner are measurably more realistic—as verified by comparison to a set of human-based measures of semantic representation—than those available from either data type individually or from both sources independently. This is not a result of merely using quantitatively more data, but rather it is because experiential and distributional data are qualitatively distinct, yet intercorrelated, types of data. The semantic representations that are learned are based on statistical structures that exist both within and between the experiential and distributional data types.

& Recent evidence has suggested that the human occipitotemporal region comprises several subregions, each sensitive to a distinct processing level of visual words. To further explore the functional architecture of visual word recognition, we employed a subliminal priming method with functional magnetic resonance imaging (fMRI) during semantic judgments of words presented in two different Japanese scripts, Kanji and Kana. Each target word was preceded by a subliminal presentation of either the same or a different word, and in the same or a different script. Behaviorally, word repetition produced significant priming regardless of whether the words were presented in the same or different script. At the neural level, this cross-script priming was associated with repetition suppression in the left inferior temporal cortex

Investigations of patients with semantic category-specific deficits have revealed a wide range of performance and variability in categories that are impaired or spared; this variability presents a challenge to accounts of category specificity. Accounts based only on impairment to semantic features of a particular type (e.g., visual), as well as accounts based only on featural properties (e.g., feature intercorrelations), are insufficient to explain the variability of patients' performance. A first goal of the paper is to discuss how a hybrid account incorporating both a level of organization according to feature-types (a level of nonlinguistic conceptual representations) and a level of organization dictated by featural properties may provide a more comprehensive account of the cases reported in the literature. The second and most novel goal of the study reported here is to derive from our hybrid account a series of novel predictions concerning the representation and impairment of a different domain of knowledge: knowledge of actions and events, a domain of knowledge that has received remarkably little attention to date. Keywords: category-specificity, nouns, verbs, semantics, simulation The breakdown of semantic knowledge: Insights from a statistical model of meaning representation. The study of patients in whom semantic knowledge has been disrupted has led to a number of important inferences concerning the underlying architecture of the semantic system (Warrington, 1975). Particularly relevant are cases in which focal brain damage creates categoryspecific deficits (i.e., selective impairment of semantic knowledge along category boundaries). At present there are a substantial number of cases on record (approximately 89, according to Rogers & Plaut, 2002). Specificity in...

INTRODUCTION The goal of the present work is to examine whether the semantic representations of numbers and body parts are associated with partially distinct cortical territories. Clinical and cognitive neuropsychology studies associate semantic deficits in both domains to lesions coarsely localized to the left parietal lobe (McCarthy and Warrington, 1990). Furthermore, patients with left inferior parietal lesions often exhibit simultaneous deficits for numbers and body parts (Benton, 1992; Gerstmann, 1940). Such an association of neuropsychological deficits is however notoriously ambiguous, and has been the subject of much debate. It might suggest that there is a shared substrate for numbers and body parts in the left parietal region, perhaps based on a common functional system for spatial representation and manipulation (Gerstmann, 1940) or on the crucial role that finger counting plays in numerical development (Butterworth, 1999). However, it might also reflect the existence of dis

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The way in which meaning is represented and processed in the brain is a key issue in cognitive neuroscience, which can be usefully addressed by functional imaging techniques. In contrast to previous imaging studies of semantic knowledge, which have primarily used blocked designs, in this study we use an eventrelated fMRI (erfMRI) design, which has the advantage of enabling events to be presented pseudorandomly, thus reducing strategic processes and enabling more direct comparison with psychological behavioral studies. We used a semantic categorization task in which events were words representing either artifact or natural kinds concepts. Significant areas of activation for semantic processing included inferior frontal lobe bilaterally (BA 47) and left temporal regions, both inferior (BA 36 and 20) and middle (BA 21). These are areas that have been identified in previous neuroimaging studies of semantic knowledge. However, there were no significant differences between artifact and natural kinds concepts. These results are consistent with our previous imaging studies using blocked designs and suggest that conceptual knowledge is represented in a unitary, distributed neural system undifferentiated by domain of knowledge. These findings demonstrate that event-related designs can generate activations that are similar to those seen in blocked designs investigating semantics and, moreover, offer a greater capacity for interpretation free from the confounds of block effects. © 2002 Elsevier Science (USA)