1/46. Impairment of depth perception in multiple sclerosis is improved by treatment with AC pulsed electromagnetic fields.multiple sclerosis (MS) is associated with postural instability and an increased risk of falling which is facilitated by a variety of factors including diminished visual acuity, diplopia, ataxia, apraxia of gait, and peripheral neuropathy. Deficient binocular depth perception may also contribute to a higher incidence of postural instability and falling in these patients who, for example, find it an extremely difficult task to walk on uneven ground, over curbs, or up and down steps. I report a 51 year old woman with secondary progressive MS who experienced difficulties with binocular depth perception resulting in frequent falls and injuries. Deficient depth perception was demonstrated also on spontaneous drawing of a cube. Following a series of transcranial treatments with AC pulsed electromagnetic fields (EMFs) of 7,5 picotesla flux density, the patient experienced a major improvement in depth perception which was evident particularly on ascending and descending stairs. These clinical changes were associated with an improvement in spatial organization and depth perception on drawing a cube. These findings suggest that in MS impairment of depth perception, which is encoded in the primary visual cortex (area 17) and visual association cortex (areas 18 and 19), may be improved by administration of AC pulsed EMFs of picotesla flux density. The primary visual cortex is densely innervated by serotonergic neurons which modulate visual information processing. Cerebral serotonin concentrations are diminished in MS patients and at least some aspects of deficient depth perception in MS may be related to dysfunction of serotonergic transmission in the primary visual cortex. It is suggested that transcranial AC pulsed applications of EMFs improve depth perception partly by augmenting serotonergic transmission in the visual cortex.- - - - - - - - - - ranking = 1keywords = information (Clic here for more details about this article) |
2/46. Tactile morphagnosia secondary to spatial deficits.A 73-year old man showed visual and tactile agnosia following bilateral haemorrhagic stroke. Tactile agnosia was present in both hands, as shown by his impaired recognition of objects, geometrical shapes, letters and nonsense shapes. Basic somatosensory functions and the appreciation of substance qualities (hylognosis) were preserved. The patient's inability to identify the stimulus shape (morphagnosia) was associated with a striking impairment in detecting the orientation of a line or a rod in two- and three-dimensional space. This spatial deficit was thought to underlie morphagnosia, since in the tactile modality form recognition is built upon the integration of the successive changes of orientation in space made by the hand as it explores the stimulus. Indirect support for this hypothesis was provided by the location of the lesions, which could not account for the severe impairment of both hands. Only those located in the right hemisphere encroached upon the posterior parietal cortex, which is the region assumed to be specialised in shape recognition. The left hemisphere damage spared the corresponding area and could not, therefore, be held responsible for the right hand tactile agnosia. We submit that tactile agnosia can result from the disruption of two discrete mechanisms and has different features. It may arise from a parietal lesion damaging the high level processing of somatosensory information that culminates in the structured description of the object. In this case, tactile recognition is impaired in the hand contralateral to the side of the lesion. Alternatively, it may be caused by a profound derangement of spatial skills, particularly those involved in detecting the orientation in space of lines, segments and complex patterns. This deficit results in morphagnosia, which affects both hands to the same degree.- - - - - - - - - - ranking = 1keywords = information (Clic here for more details about this article) |
3/46. Pathological perceptual completion in hemianopia extends to the control of reach-to-grasp movements.The neuropsychological phenomenon of blindsight is observed when patients who are cortically blind exhibit residual visual processing capabilities for stimuli presented within their scotoma to which they are otherwise unaware. Cortically blind patients may also exhibit the phenomenon of pathological visual completion in which, paradoxically, they can become aware of a complete visual stimulus even when a significant portion of that stimulus falls within their blind hemifield. In this study, the ability of a blindsight patient (G.Y.) to use visual information to control reach-to-grasp movements to static objects presented within his blind hemifield was investigated. The results indicate that while G.Y. was insensitive to variations in object size when reaching for objects presented entirely within his blind hemifield, his ability to accurately grasp objects located within his blind field was vastly improved if part of the object to be grasped extended into his seeing hemifield. This finding demonstrates that visual awareness can facilitate the visuomotor processing of object form within G.Y.'s apparently blind field, and suggests that the primary deficit in blindsight may be an impairment of visual consciousness rather than an absolute loss of visual function.- - - - - - - - - - ranking = 1keywords = information (Clic here for more details about this article) |
4/46. Faces call for attention: evidence from patients with visual extinction.Three patients with left spatial neglect and visual extinction from right brain damage were studied to determine whether faces are privileged in summoning attention. In a first experiment, either a face, a name, or a meaningless shape were briefly presented in the right, left or both visual hemifields. On bilateral trials, all patients extinguished a left-side face much less often than a left-side name or a left-side shape. Conversely, they extinguished a left-side shape more often when it was accompanied by a right-side face rather than a right-side name. In a second experiment, either a face or a scrambled face could appear in the right, left or both hemifields. Again, on bilateral trials, a left-side face was less likely to be missed than a scrambled one. These results suggest an advantage of faces in capturing attention and overcoming extinction, which may be related to their special biological and social value, or to the very efficient and automatic operation of specific perceptual processses that extract facial organization in extrastriate visual areas. These findings also demonstrate that the distribution of spatial attention and extinction can be modulated by the relevance of visual stimuli. This implies that substantial analysis and categorization may take place in the visual system before information from the contralesional field is selected for, or excluded from, attentive vision.- - - - - - - - - - ranking = 1keywords = information (Clic here for more details about this article) |
5/46. Interhemispheric transfer time in a patient with a partial lesion of the corpus callosum.The interhemispheric transfer time (ITT) of basic visuo-motor integration was investigated in a patient who had a lesion of the corpus callosum that spared the splenium and rostrum. overall, 4291 simple reaction times were collected during unimanual responses to tachistoscopically presented lateralized simple visual stimuli at 4 degrees, 6 degrees and 10 degrees. Despite retaining some abilities that typically require the integration of information between hemispheres (e.g. haptic naming, tachistoscopic lateralized consonant reading) the patient performed similarly to completely callosotomized patients in a basic visuo-motor ITT task (overall 25.5 ms) at any eccentricity. These findings suggest that specific callosal channels mediate the basic visuo-motor ITT and these do not include the rostrum and/or the splenium of the corpus callosum.- - - - - - - - - - ranking = 1keywords = information (Clic here for more details about this article) |
6/46. Naming of musical notes: a selective deficit in one musical clef.We investigated the ability to perform solfeggio, i.e. oral reading of musical notes in MP, a 65 year-old female professional musician, who, following a left temporoparietal ischemia, showed a complex pattern of amusia. The deficit on which we focused was her inability to read orally the bass (F) clef, often substituting it with the violin (G) clef. This problem could not be attributed to a lack of comprehension. The patient could in fact correctly perform on the piano the same sequences she erroneously read aloud; she was also able to correctly judge whether two strings, one in bass clef and the other in violin clef, represented the same sequence of notes. The problem seems to lie in the inability to retrieve note names keeping into account the clef-rule. It is hypothesized that, in the production of note names, this function requires the identification and application of syntactic-like information, in analogy with what is thought to happen in the retrieval of other words.- - - - - - - - - - ranking = 1keywords = information (Clic here for more details about this article) |
7/46. prosopagnosia: a case study involving problems in processing configural information.An ongoing issue in face recognition research is whether holistic face processing relies on the segregation of local discrete facial parts. Evidence in favor of the holistic-plus-parts view stems from a recent study reported by Arguin and Saumier (1999), who show that the priming effects of individual facial parts (i.e., eyes, nose, mouth, orcontour) depends on the presence of configural information and that the magnitude of priming augments as the number of facial parts serving as primes increase. The present study demonstrates that these global processing effects are absent in a prosopagnosic patient (A.R.), who shows no priming from single face parts and a linear increase in the magnitude of priming as a function of the number of parts presented. These findings indicate that A.R. is incapable of integrating individual facial parts into a global facial configuration ant that this is likely at the root of her prosopagnosia.- - - - - - - - - - ranking = 5keywords = information (Clic here for more details about this article) |
8/46. face context interferes with local part processing in a prosopagnosic patient.We investigated the role of local and global information on perceptual encoding of faces in patient HJA, who shows prosopagnosia and visual agnosia following occipito-temporal damage. HJA and an age-matched control were tested in a simultaneous matching task which focused on detection of local changes in faces: the inversion of central parts (eyes and mouth) relative to their context (as in the Thatcher illusion). Same-different judgements were made to normal, "that cherised" and mixed type face pairs. Whole faces (Experiment 1), or face parts (Experiment 2), were presented in upright and inverted orientations. Compared to the control, HJA was severely impaired at matching whole faces, but he improved dramatically when face parts were presented in isolation. This suggests an inhibitory influence of face context on HJAs processing of local parts and a relatively intact ability to process part-based information from a face (when context cannot interfere). face inversion did not affect HJAs performance. A control experiment (Experiment 3) with non-face stimuli (houses) suggested that the inhibitory influence of context on HJAs performance was restricted to faces. These results indicate that contextual information in a face can have an adverse influence on the processing of local part-based information in prosopagnosia.- - - - - - - - - - ranking = 4keywords = information (Clic here for more details about this article) |
9/46. Neuropsychologic assessment of visual disorders.This article introduces the reader to a sample of visual tests used in the neuropsychologic assessment of patients who present with various visual deficits. As discussed, patients often present with visual abnormalities that cannot be assessed exclusively during the opthtalmologic examination, partly because these problems extend beyond the fundamental aspects of visual processing. Visual problems occur in the context of focal or diffuse brain damage. Neuropsychologic evaluation can provide valuable diagnostic information and information regarding functional strengths and weaknesses. Many visual tests have been developed for clinical use. Some of these tests have been validated with lesion analytic or neuroimaging studies, which highlight the areas of the brain presumed necessary for task performance. knowledge regarding the neural substrates of test performance allows the clinician to identify the neuropathologic correlates of test failure, which, in turn, is relevant to differential diagnosis. A profile of functional strengths and weaknesses emerges contributing to the treatment of the patient with a visual disorder. In this article, the authors present a subset of visual tests used primarily in the clinical setting. Some of these tests measure lower-level visual deficits (e.g., judgment of Line orientation) and others measure higher-level visual/cognitive deficits (e.g., ROCF). Although no firm delineation of test subtypes exists, the authors divide the tests into general categories of visuoperceptual, visuospatial, visuoconstructive, and visual attention/memory. Ultimately, it is incumbent on a trained neuropsychologist to select appropriate visual tests based on the patient's described symptoms and the referral question.- - - - - - - - - - ranking = 2keywords = information (Clic here for more details about this article) |
10/46. A case of unilateral neglect in Huntington's disease.Unilateral neglect, an attentional deficit in detecting and acting on information coming from one side of space, is a relatively common consequence of right hemisphere stroke. Although neglect has been observed following damage to a variety of brain structures, to date no reports exist of neglect phenomena arising from Huntington's disease (HD). However, reports in the animal and human literature suggest that neglect is possible following damage to a primary site for Huntington's pathology, the basal ganglia. Here we present a patient (BG) with genetically proven HD who, in the context of the mild intellectual, executive and attentional impairments associated with the disorder, showed a remarkably severe and stable neglect for left space. MRI and electrophysiological results make it unlikely that the spatial bias could be accounted for by basic sensory loss. In addition, behavioural investigation indicated that, although BG's neglect operated in a very striking manner along body-centred co-ordinates (missing almost all information presented to her left), more general limitations in visual attention were apparent to the left-side of information presented entirely to the right of the body midline. Further evidence is presented showing that the neglect was manifest on tactile and auditory tasks as well as those presented in the visual domain. The presence of neglect in HD in this case is novel and somewhat puzzling, particularly as flourodeoyglucose positron emission tomography revealed bilateral caudate hypoperfusion. Reducing the statistical threshold on this analysis revealed a potential frontal hypometabolism that was more marked in the right than left hemisphere. However, as this was only apparent at a threshold below that normally considered acceptable (due to the resulting number of false positives), this possible account of the neglect must be viewed very cautiously.- - - - - - - - - - ranking = 3keywords = information (Clic here for more details about this article) |
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