1/180. Visual environmental rotation: a novel disorder of visiospatial integration.A 70-year-old man experienced an unusual disorder of visual perception after undergoing a ventriculoperitoneal shunt for normal-pressure hydrocephalus. The disorder was characterized by transient episodes of 90 degrees rotation of the visual environment, rather than the retinotopic visual field. This phenomenon is different from standard visual allesthesia and may have been caused by disordered integration of vestibular and visual inputs to the posterior parietal cortex or perseveration of a pre-existing environmental memory trace.- - - - - - - - - - ranking = 1keywords = visual (Clic here for more details about this article) |
2/180. Palinopsia with bacterial brain abscess and noonan syndrome.Though positive visual symptoms can be psychological in nature, or can result from a perceptive or anxious patients recognizing optical principals in the eye itself, this case illustrates how a thorough history is required to delineate those rarer signs which accompany serious macular or neuro-ophthalmic pathology.- - - - - - - - - - ranking = 0.2keywords = visual (Clic here for more details about this article) |
3/180. Residual perceptual distortion in 'recovered' hemispatial neglect.In most neglect patients, line bisection errors become smaller on repeated tests over the months following the lesion. We have tried to determine in two typical patients whether this is because of a real reduction in the perceptual distortions that appear to underlie line bisection errors in neglect, or whether it reflects a learned behavioural strategy to counteract those perceptual biases. We tested the patients on two occasions (2 and 12 months post-stroke), on line bisection and also on the 'Landmark' task. The data indicated that at the first testing session both patients showed strong 'perceptual' neglect, making large rightward errors in the standard bisection task and uniformly leftward pointing in the Landmark task. On the second occasion, as expected, both patients showed a marked recovery when tested with the line bisection task, making only very small errors. In contrast, their landmark performance was still markedly biased in the same direction as before. These findings suggest that despite their apparent recovery on the bisection task, both patients still experience some form of perceptual distortion of horizontal lines. It is suggested that the Landmark task may provide a sensitive means for identifying real recovery of the underlying perceptual deficit.- - - - - - - - - - ranking = 0.0049506621830977keywords = contrast (Clic here for more details about this article) |
4/180. 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 = 1.4keywords = visual (Clic here for more details about this article) |
5/180. Subcortical mechanisms in language: lexical-semantic mechanisms and the thalamus.Four previously published cases of dominant thalamic lesion in which the author has participated are reviewed to gain a better understanding of thalamic participation in lexical-semantic functions. Naming deficits in two cases support Nadeau and Crosson's (1997) hypothesis of a selective engagement mechanism involving the frontal lobes, inferior thalamic peduncle, nucleus reticularis, and other thalamic nuclei, possibly the centromedian nucleus. This mechanism selectively engages those cortical areas required to perform a cognitive task, while maintaining other areas in a state of relative disengagement. Deficits in selective engagement disproportionately affect lexical retrieval based on semantic input, as opposed to lexical and sublexical processes, because the former is more dependent upon this attentional system. The concept of selective engagement is also useful in understanding thalamic participation in working memory, as supported by data from one recent functional neuroimaging study. Other processes also may be compromised in more posterior thalamic lesions which damage the pulvinar but not other components of this selective engagement system. A third case with aphasia after a more superior and posterior thalamic lesion also had oral reading errors similar to those in neglect dyslexia. The pattern of deficits suggested a visual processing problem in the early stages of reading. The fourth case had a category-specific naming deficit after posterior thalamic lesion. Taken together, the latter two cases indicate that the nature of language functions in more posterior regions of the dominant thalamus depends upon the cortical connectivity of the thalamic region. Together, findings from the four cases suggest that thalamic nuclei and systems are involved in multiple processes which directly or indirectly support cortical language functions.- - - - - - - - - - ranking = 0.2keywords = visual (Clic here for more details about this article) |
6/180. Pointing and grasping in unilateral visual neglect: effect of on-line visual feedback in grasping.Three experiments are reported examining judgements of the centre of a stick in a patient with unilateral neglect after right hemisphere damage. Replicating previous data [35, 37], judgements showed more evidence of neglect when pointing rather than when a grasp response was used (Experiment 1), particularly when pointing preceded grasp (Experiment 2). Neglect also increased for longer sticks and when sticks fell in the patient's left hemispace; the effects of stick length and hemispace were additive with those of response (point vs grasp). Experiment 3 showed that the advantage for grasp over pointing responses occurred only when performance was guided by on-line visual feedback, and it emerged only during the end part of the reach trajectory. The results are discussed in relation to the role of visual feedback in movement control.- - - - - - - - - - ranking = 2keywords = visual (Clic here for more details about this article) |
7/180. 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 = 0.2keywords = visual (Clic here for more details about this article) |
8/180. 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 = 1.4keywords = visual (Clic here for more details about this article) |
9/180. Akinetopsia from nefazodone toxicity.PURPOSE: To investigate two cases of selective impairment of motion perception (akinetopsia) induced by toxicity from the antidepressant nefazodone, a new drug that blocks serotonin reuptake and antagonizes 5-HT2 receptors. methods: case reports. RESULTS: A 47-year-old man receiving nefazodone (Serzone; Bristol-Meyers Squibb, new york, N.Y.) (100 mg twice daily), reported a bizarre derangement of motion perception. Moving objects were followed by a trail of multiple "freeze-frame" images, which dissipated promptly when motion ceased. A 48-year-old woman receiving nefazodone (400 mg daily at bedtime) reported a similar phenomenon, with visual trails following moving objects. In both patients, vision returned to normal after the dosage of nefazodone was reduced or eliminated. CONCLUSIONS: Nefazodone toxicity can result in akinetopsia, characterized by the inability to perceive motion in a normal, smooth fashion; persistence of multiple, strobelike images; and visual trails behind moving objects. In this rare syndrome, stationary elements are perceived normally, indicating that nefazodone causes selective impairment of pathways involved in motion processing in the visual system.- - - - - - - - - - ranking = 0.6keywords = visual (Clic here for more details about this article) |
10/180. Oscillopsia and pseudonystagmus in kidney transplant patients.PURPOSE: Modern immunosuppressants have improved the success of kidney transplantation for renal failure patients. They also may induce neurotoxic effects including tremor. We report two cases of pseudonystagmus and oscillopsia in transplant patients caused by immunosuppressant-induced head tremor and gentamicin-induced vestibulotoxicity. methods: case reports. head tremor, static visual acuity, and dynamic visual acuity were measured. Vestibular function was evaluated with ice water calorics. RESULTS: Both patients had significant head tremor and pseudonystagmus. head stabilization improved static visual acuity. Dynamic visual acuity revealed a 4-line and 10-line loss of visual acuity, respectively. CONCLUSIONS: These findings of pseudonystagmus and oscillopsia are likely to become more prevalent as more renal failure patients receive transplants. Improvement may be seen with reduction of immunosuppressant, reduction of stimulant intake, use of medications to reduce head tremor, and vestibular rehabilitation.- - - - - - - - - - ranking = 1keywords = visual (Clic here for more details about this article) |
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