bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Spurious Category-Specific Visual Agnosia for Living Things in Normal Human and Nonhuman Primates
Authors: Gaffan David , Heywood Charles A. 
Published: February 2008

Abstract
Patients with visual associative agnosia have a particular difficulty in identifying visually presented living things (plants and animals) as opposed to nonliving things. It has been claimed that this effect cannot be explained by differences in the inherent visual discriminability of living and nonliving things. To test this claim further, we performed two experiments with normal subjects. In Experiment 1 normal human observers were asked to identify objects in tachistoscopically presented line drawings. They made more errors with living things than with nonliving things. In Experiment 2 normal monkeys learned to discriminate among the same line drawings for food reward. They made many more errors in discriminating among living things than nonliving things. Agnosic patients' responses to the same line drawings were made available to us for correlative analysis with the subjects' responses to these drawings in Experiments 1 and 2. We conclude that a category-specific visual agnosia for living things can arise as a consequence of a modality-specific but not category-specific impairment in visual representation, since living things are more similar to each other visually than nonliving things are.
Differential Effects of Semantic and Identity Priming in Patients with Left and Right Hemisphere Lesions
Authors: Henik Avishai , Dronkers Nina F. , Knight Robert T. , Osimani Alicia 
Published: February 2008

Abstract
Patients with single brain lesions in the anterior or posterior left and right hemispheres and a group of controls were studied in two priming experiments. The first experiment employed associative pairs (DOCTOR-NURSE) and the second employed identical pairs (NURSE-nurse). Short and long prime-target stimulus onset asynchronies (SOAs) (i.e., 250 and 1850 msec) were manipulated within block in both experiments. In the first experiment, patients with left hemisphere injury showed a deficient priming effect while patients with right hemisphere injury and controls showed a normal pattern. In contrast, all groups showed an identity priming effect in the second experiment. These results indicate that while entries in the mental lexicon are available for the groups of patients studied, the spread of activation to related concepts in this lexicon is disrupted in the left hemisphere-damaged group.
Visual Mental Imagery Activates Topographically Organized Visual Cortex: PET Investigations
Authors: Kosslyn Stephen M. , Alpert Nathaniel M. , Thompson William L. , Maljkovic Vera , Weise Steven B. , Chabris Christopher F. , Hamilton Sania E. , Rauch Scott L. , Buonanno Ferdinando S. 
Published: February 2008

Abstract
Cerebral blood flow was measured using positron emission tomography (PET) in three experiments while subjects performed mental imagery or analogous perceptual tasks. In Experiment 1, the subjects either visualized letters in grids and decided whether an X mark would have fallen on each letter if it were actually in the grid, or they saw letters in grids and decided whether an X mark fell on each letter. A region identified as part of area 17 by the Talairach and Tournoux (1988) atlas, in addition to other areas involved in vision, was activated more in the mental imagery task than in the perception task. In Experiment 2, the identical stimuli were presented in imagery and baseline conditions, but subjects were asked to form images only in the imagery condition; the portion of area 17 that was more active in the imagery condition of Experiment 1 was also more activated in imagery than in the baseline condition, as was part of area 18. Subjects also were tested with degraded perceptual stimuli, which caused visual cortex to be activated to the same degree in imagery and perception. In both Experiments 1 and 2, however, imagery selectively activated the extreme anterior part of what was identified as area 17, which is inconsistent with the relatively small size of the imaged stimuli. These results, then, suggest that imagery may have activated another region just anterior to area 17. In Experiment 3, subjects were instructed to close their eyes and evaluate visual mental images of upper case letters that were formed at a small size or large size. The small mental images engendered more activation in the posterior portion of visual cortex, and the large mental images engendered more activation in anterior portions of visual cortex. This finding is strong evidence that imagery activates topographically mapped cortex. The activated regions were also consistent with their being localized in area 17. Finally, additional results were consistent with the existence of two types of imagery, one that rests on allocating attention to form a pattern and one that rests on activating stored visual memories.
Dissociation of Brain Activity Related to Syntactic and Semantic Aspects of Language
Authors: Münte Thomas F. , Heinze Hans-Jochen , Mangun George R 
Published: February 2008

Abstract
In psycholinguistic research, there has been considerable interest in understanding the interactions of difFerent types of linguistic information during language processing. For example, does syntactic information interact with semantic or pragmatic information at an early stage of language processing, or only at later stages in order to resolve ambiguities of language? Developing reliable measures of language processes such as syntax and semantics is important to address many of these theoretical issues in psycholinguistics. In the present study, event-related brain potentials (ERPs) were recorded from healthy young subjects while they read pairs of words presented one word at a time. The ERPs for the second word of each pair were compared as a function of whether the preceding word was or was not (1) semantically related (i.e., synonyms; “semantic condition”) or (2) grammatically correct (“syntactic condition”). In the semantic condition the ERPs obtained to words preceded by nonsemantically related words elicited an N400 component that was maximal over centroparietal scalp regions. In contrast, in the syntactic condition the ERPs obtained to words preceded by grammatically incorrect articles or pronouns yielded a negativity with a later onset, and a frontopolar, left hemisphere scalp maximum. This replicates our previous findings of a syntactic negativity in a word pair design that was performed in the German language. Further, the present data provide scalp distributional information, which suggests that the syntactic negativity represents brain processes that are dissociable from the centroparietal N400 component. Thus, these findings provide strong evidence for a separate negative polarity ERP component that indexes syntactic aspects of language processing.
The Human Auditory Sensory Memory Trace Persists about 10 sec: Neuromagnetic Evidence
Authors: Sams Mikko , Hari Riitta , Rif Josi , Knuutila Jukka 
Published: February 2008

Abstract
Neuromagnetic responses were recorded to frequent "standard tones of l000 Hz and to infrequent 1100-Hz "deviant" tones with a 24-channel planar SQUID gradiometer. Stimuli were presented at constant interstimulus intervals (ISIs) ranging from 0.75 to 12 sec. The standards evoked a prominent 100-msec response, N100m, which increased in amplitude with increasing ISI. N100m could be dissociated into two subcomponents with different source areas. The posterior component, N100m2, increased when the ISI grew up to 6 sec, whereas the more anterior component, N100m2, probably continued its growth beyond the 12-sec ISI. At ISIs from 0.75 to 9 sec, the deviants elicited additionally a mismatch field (MMF). The equivalent sources of both N100m and MMF were at the supra-temporal auditory cortex. We assume that auditory stimuli leave in the auditory system a trace that affects the processing of the subsequent stimuli. The decrement of the N100m amplitude as well as elicitation of MMF can be considered as indirect evidence of active traces. A behavioral estimate of the persistence of the sensory auditory memory was obtained in a separate experiment in which the subject compared, without attending to the stimuli, tones presented at the daerent ISIs. The subjects discriminated the stimuli better than merely by chance at ISIs of 0.75-9 sec. The ISI dependence of the behavioral estimate as well as of N100m2 and MMF are similar enough to suggest a common underlying mechanism that retains information for a period of about 10 sec.
Cognitive and Physiological Substrates of Impaired Sentence Processing in Parkinson's Disease
Authors: Grossman Murray , Carvell Susan , Gollomp Stephen , Stern Matthew B. , Reivich Martin , Morrison Donald , Alavi Abass , Hurtig Howard I. 
Published: February 2008

Abstract
Sentence comprehension is a complex process involving at least a grammatical processor and a procedural component that supports language computations. One type of cerebral architecture that may underlie sentence processing is a network of distributed brain regions. We report two experiments designed to evaluate the cognitive and physiological substrate of sentence processing diaculties in nondemented patients with Parkinson's disease (PD). In the first experiment, patients answered simple questions about sentences that varied in their computational demands. Group and individual patient analyses indicated that PD patients are significantly compromised on this task, and that their difficulties become more prominent as the computational demands of the sentences increase. We manipulated the set of sentences to stress performance aspects of sentence processing. PD patients were compromised in their ability to detect errors in the presence and nature of a sentence's grammatical morphemes, suggesting a deficit in selective attention, but their ability to answer questions about a sentence was not afFected by short-term memory factors. In the second experiment, positron emission tomography was used to correlate this pattern of sentence comprehension impairment with regional cerebral glucose metabolism (rCMRgl) obtained at rest in a representative subset of these PD patients. Grammatical comprehension and attention in sentence processing correlated significantly with mesial frontal rCMRgl. Regression analyses confirmed the central role of left mesial frontal cortex, and identified a subsidiary role for left caudate in overall sentence comprehension, for left dorsolateral frontal cortex in grammatical processing, and for bilateral dorsolateral frontal cortex in attending to the presence of grammatical features. We conclude that compromised mesial frontal functioning underlies in part the sentence processing deficit of these patients, and these data illustrate one method for mapping portions of a sentence processing mechanism onto a distributed cerebral architecture.
Object-Centered Neglect in Patients with Unilateral Neglect: Effects of Left-Right Coordinates of Objects
Authors: Behrmann Marlene , Moscovitch Morris 
Published: February 2008

Abstract
When patients with right-sided hemispheric lesions neglect information on the left side, with respect to what set of spatial coordinates is left defined? Two potential reference frames were examined in this study, one where left and right are defined with respect to the midline of the viewer and/or environment (viewer/env-centered) and the other where left and right are defined with respect to the midline of the object (object-centered). By rotating the stimulus 90° clockwise or counterclockwise, and instructing patients with neglect to report the colors appearing around the border of a stimulus, an independent measure was obtained for the number of colors reported from the left and right of the viewer/env- and from the object-based reference frame. Whereas significant object-centered neglect was observed only for upper case asymmetrical letters but not for symmetrical letters nor for drawings of familiar animals or objects, significant viewer/env-based neglect was observed with all the stimulus types. We present an account of the coexistence of neglect in more than one frame of reference and the presence of object-centered neglect under a restricted set of conditions.
Summation Priming and Coarse Semantic Coding in the Right Hemisphere
Authors: Beeman Mark , Friedman Rhonda B. , Grafman Jordan , Perez Enrique , Diamond Sherri , Lindsay Miriam Beadle 
Published: February 2008

Abstract
There are now numerous observations of subtle right hemisphere (RH) contributions to language comprehension. It has been suggested that these contributions reflect coarse semantic coding in the RH. That is, the RH weakly activates large semantic fields—including concepts distantly related to the input word—whereas the left hemisphere (LH) strongly activates small semantic fields—limited to concepts closely related to the input (Beeman, 1993a,b). This makes the RH less effective at interpreting single words, but more sensitive to semantic overlap of multiple words. To test this theory, subjects read target words preceded by either “Summation” primes (three words each weakly related to the target) or Unrelated primes (three unrelated words), and target exposure duration was manipulated so that subjects correctly named about half the target words in each hemifield. In Experiment 1, subjects benefited more from Summation primes when naming target words presented to the left visual field-RH (Ivf-RH) than when naming target words presented to the right visual field-LH (rvf-LH), suggesting a RH advantage in coarse semantic coding. In Experiment 2, with a low proportion of related prime-target trials, subjects benefited more from “Direct” primes (one strong associate flanked by two unrelated words) than from Summation primes for rvf-LH target words, indicating that the LH activates closely related information much more strongly than distantly related information. Subjects benefited equally from both prime types for Ivf-RH target words, indicating that the RH activates closely related information only slightly more strongly, at best, than distantly related information. This suggests that the RH processes words with relatively coarser coding than the LH, a conclusion consistent with a recent suggestion that the RH coarsely codes visual input (Kosslyn, Chabris, Mar-solek, & Koenig, 1992).
Learning and Maintaining Saccadic Accuracy: A Model of Brainstem–Cerebellar Interactions
Authors: Dean Paul , Mayhew John E. W. , Langdon Pat 
Published: February 2008

Abstract
Saccadic accuracy requires that the control signal sent to the motor neurons must be the right size to bring the fovea to the target, whatever the initial position of the eyes (and corresponding state of the eye muscles). Clinical and experimental evidence indicates that the basic machinery for generating saccadic eye movements, located in the brainstem, is not accurate: learning to make accurate saccades requires cerebellar circuitry located in the posterior vermis and fastigial nucleus. How do these two circuits interact to achieve adaptive control of saccades? A model of this interaction is described, based on Kawato's principle of feedback-error-learning. Its three components were (1) a simple controller with no knowledge of initial eye position, corresponding to the superior colliculus; (2) Robinson's internal feedback model of the saccadic burst generator, corresponding to preoculomotor areas in the brain-stem; and (3) Albus's Cerebellar Model Arithmetic Computer (CMK), a neural net model of the cerebellum. The connections between these components were (I) the simple feedback controller passed a (usually inaccurate) command to the pulse generator, and (2) a copy of this command to the CMAC; (3) the CMAC combined the copy with information about initial eye position to (4) alter the gain on the pulse generator's internal feedback loop, thereby adjusting the size of burst sent to the motor neurons. (5) If the saccade were inaccurate, an error signal from the feedback controller adjusted the weights in the CMAC. It was proposed that connection (2) corresponds to the mossy fiber projection from superior colliculus to oculomotor vermis via the nucleus reticularis tegmenti pontis, and connection (5) to the climbing fiber projection from superior colliculus to the oculomotor vermis via the inferior olive. Plausible initialization values were chosen so that the system produced hypometric saccades (as do human infants) at the start of learning, and position-dependent hypermetric saccades when the cerebellum was removed. Simulations for horizontal eye movements showed that accurate saccades from any starting position could be learned rapidly, even if the error signal conveyed only whether the initial saccade were too large or too small. In subsequent tests the model adapted realistically both to simulated weakening of the eye muscles, and to intrasaccadic displacement of the target, thereby mimicking saccadic plasticity in adults. The architecture of the model may therefore offer a functional explanation of hitherto mysterious tectocerebellar projections, and a framework for investigating in greater detail how the cerebellum adaptively controls saccadic accuracy.
Duration of EEG and MEG α Suppression Increases with Angle in a Mental Rotation Task
Authors: Michel Christoph M. , Kaufman Lloyd , Williamson Samuel J. 
Published: February 2008

Abstract
Electric and magnetic recordings of average power within the high a band (10–12 Hz) were made over the parietal and occipital areas of the scalp while subjects were engaged in the mental imagery task of Cooper and Shepard. The subject had to determine whether an abstract probe figure was identical to a memory figure presented earlier at a different orientation, or whether it was the mirror image of the memory figure. Alpha power was found to be suppressed while the subjects were engaged in the comparison, and the duration of suppression increased with the minimum rotation angle to achieve a match. Strong correlations between suppression duration and reaction time give further evidence that the visual cortex is engaged in the process of mental imagery. Moreover, for large rotation angles of the probe figures, where the task is markedly more difficult, a shift in the spatial pattern of suppression indicates some additional activity in left occipital areas.
Visual Attention in Children with Perinatal Brain Injury: Asymmetric Effects of Bilateral Lesions
Authors: Craft Suzanne , White Desiree A. , Park T. S. , Figiel Gary 
Published: February 2008

Abstract
The neural systems underlying visual attention have been well-documented in adults through studies examining the effects of brain lesions on specific attentional operations (Posner, Cohen, & Rafal, 1982). The questions of how this attentional system develops and how it is affected by disruption during development are only beginning to be addressed. In the present study, a covert orienting task (Posner et al., 1982) was administered to 33 children with bilateral perinatal injury to anterior, posterior, or diffuse brain regions and 36 normal children to determine the effects of such injury on visual attention. Children with bilateral anterior lesions showed lateralized impairment indicating compromise of left hemisphere early attentional processes. In contrast, children with posterior lesions that typically disrupt attention in adults showed only general slowing, with no differences in right or left visual field performance or deficits in specific attentional operations. These results suggest that anterior brain regions play an important role in the development of visual attention, and that left hemisphere attentional processes are particularly affected by disruption of anterior function.
Neural Representations for Sensorimotor Control. III. Learning a Body-Centered Representation of a Three-Dimensional Target Position
Authors: Guenther Frank H. , Bullock Daniel , Greve Douglas , Grossberg Stephen 
Published: February 2008

Abstract
A neural model is described of how the brain may autonomously learn a body-centered representation of a three-dimensional (3-D) target position by combining information about retinal target position, eye position, and head position in real time. Such a body-centered spatial representation enables accurate movement commands to the limbs to be generated despite changes in the spatial relationships between the eyes, head, body, and limbs through time. The model learns a vector representation—otherwise known as a parcellated distributed representation—of target vergence with respect to the two eyes, and of the horizontal and vertical spherical angles of the target with respect to a cyclopean egocenter. Such a vergence-spherical representation has been reported in the caudal midbrain and medulla of the frog, as well as in psychophysical movement studies in humans. A head-centered vergence-spherical representation of foveated target position can be generated by two stages of opponent processing that combine corollary discharges of outflow movement signals to the two eyes. Sums and differences of opponent signals define angular and vergence coordinates, respectively. The head-centered representation interacts with a binocular visual representation of nonfoveated target position to learn a visuomotor representation of both foveated and nonfoveated target position that is capable of commanding yoked eye movements. This head-centered vector representation also interacts with representations of neck movement commands to learn a body-centered estimate of target position that is capable of Commanding coordinated arm movements. Learning occurs during head movements made while gaze remains fixed on a foveated target. An initial estimate is stored and a VOR-mediated gating signal prevents the stored estimate from being reset during a gaze-maintaining head movement. As the head moves, new estimates are compared with the stored estimate to compute difference vectors which act as error signals that drive the learning process, as well as control the on-line merging of multimodal information.
Do Rats Have Prefrontal Cortex? The Rose-Woolsey-Akert Program Reconsidered
Authors: Preuss Todd M. 
Published: February 2008

Abstract
Primates are unique among mammals in possessing a region of dorsolateral prefrontal cortex with a well-developed internal granular layer. This region is commonly implicated in higher cognitive functions. Despite the histological distinctiveness of primate dorsolateral prefrontal cortex, the work of Rose, Woolsey, and Akert produced a broad consensus among neuroscientists that homologues of primate granular frontal cortex exist in nonprimates and can be recognized by their dense innervation from the mediodorsal thalamic nucleus (MD). Additional characteristics have come to be identified with dorsolateral prefrontal cortex, including rich dopaminergic innervation and involvement in spatial delayed-reaction tasks. However, recent studies reveal that these characteristics are not distinctive of the dorsolateral prefrontal region in primates: MD and dopaminergic projections are widespread in the frontal lobe, and medial and orbital frontal areas may play a role in delay tasks. A reevaluation of rat frontal cortex suggests that the medial frontal cortex, usually considered to be homologous to the dorsolateral prefrontal cortex of primates, actually consists of cortex homologous to primate premotor and anterior cin-date cortex. The lateral MD-projection cortex of rats resembles portions of primate orbital cortex. If prefrontal cortex is construed broadly enough to include orbital and cingulate cortex, rats can be said to have prefrontal cortex. However, they evidently lack homologues of the dorsolateral prefrontal areas of primates. This assessment suggests that rats probably do not provide useful models of human dorsolateral frontal lobe function and dysfunction, although they might prove valuable for understanding other regions of frontal cortex.