Seizure induction and magnetic brain stimulation after stroke.
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Cerebrovascular Disorders↗
Biomedical subjects
J Zihl
Publications and source records attributed to J Zihl.
Reduced binocular depth inversion as an indicator of cannabis-induced censorship impairment.
Measurements of binocular depth inversion using a stereoscopic slide projection with polarized light were performed in healthy volunteers before and after cannabis intake. Since binocular depth inversion represents an illusion occurring in the perception of semantically meaningful objects projected in a 3-D inverted fashion, the hypothesis can be tested that cannabis-induced "psychedelic states" represent a condition in which the human CNS is unable to correct implausible perceptual hypotheses. The data demonstrate a strong cannabis-induced impairment of binocular depth inversion.
Adult↗
Disturbance of movement vision after bilateral posterior brain damage. Further evidence and follow up observations.
In 1983 we reported in this Journal a patient who suffered a disturbance of movement vision in a relatively pure form. This uncommon cerebral visual deficit resulted as a consequence of bilateral brain damage affecting the lateral temporo-occipital cortex and the underlying white matter. In this paper we present further evidence for the selectivity of the movement vision deficit. Furthermore, follow-up examination did not reveal any significant change which indicates that the disorder appears irreversible. Magnetic Resonance Imaging (MRI) shows bilateral lesions involving the upper (cranial) part of the occipital gyri and the adjacent portion of the middle temporal gyri, with the main focus of damage in the upper (cranial) banks of the anterior occipital sulcus. In addition, cortico-cortical fibre pathways interconnecting occipital, temporal and parietal 'visual' areas are also affected bilaterally. The selectivity of the movement vision deficit and the irreversibility of the disorder strongly support the idea that movement vision is a separate function which is subserved by a visual pathway specialized for the processing of visual motion.
Brain Diseases↗
Residual motion perception in a "motion-blind" patient, assessed with limited-lifetime random dot stimuli.
A neurological patient (L.M.) suffering a specific loss of visual motion perception (Zihl et al., 1983) due to extrastriate cortical damage was studied using random dot "limited-lifetime" stimuli with a direction discrimination task. With a stimulus like that of Newsome and Pare (1988), the patient exhibited a severe deficit for motion perception, only being able to perform well for very high values of coherence. Different versions of the stimulus were employed to separate out the effects of limited lifetime versus the effects of additive noise as coherence was lowered. When all "signal" dots had a fixed, specified value of lifetime, and varying percentages of "noise" dots were added, the patient showed a profound deficit. In contrast, a stimulus consisting of no noise dots at all, and signal dots having fixed values of lifetime, revealed relatively good performance for surprisingly brief dot lifetimes. Thus, it is the presence of noisy, incoherent dot motion, rather than brief lifetimes, that causes such poor performance on the stimulus of Newsome and Pare (1988). Most surprising was the finding that the presence of even very small percentages of stationary noise dots was sufficient to disrupt totally direction discrimination of moving signal dots. The findings reported here suggest that one major role of extrastriate cortical processing might be the interpretation of stimuli that suffer from an impaired signal-to-noise ratio; the most commonly encountered form of "noise" would presumably be contamination by irrelevant directional spatio-temporal frequency components.
Humans↗
Reduced dark-adaptation: an indication of lithium's neuronal action in humans.
Although lithium plays a major role in therapy and prophylaxis of affective psychoses, no direct indication of its neuronal action in humans exists. A lithium-induced strong reduction of foveal dark-adaptation was found in healthy volunteers, and a lithium-induced reduction was also measured in patients with affective psychoses. Dark-adaptation measurements apparently offer the opportunity for in vivo monitoring of lithium's CNS effects in humans and may predict lithium's clinical efficacy.
Adaptation, Ocular↗
[Anamnesis of brain-originated vision disorders].
A questionnaire for the subjective assessment of cerebral visual disorders was administered to 269 brain damaged patients. The patients' subjective complaints were correlated with the outcome of objective diagnostic procedures (visual perimetry, visual search, spatial contrast sensitivity, visual evoked potentials, depth perception, light- and dark-adaptation, reading, colour vision). A significant correlation was found between subjective complaints and objective diagnostic results for all fields. The prediction of visual impairments on the basis of subjective complaints and verified by objective tests was correct in 80 to 98% of the brain damaged patients tested. Interrater reliability was about 0.84. Thus, the questionnaire is suitable for the assessment of cerebral visual disorders because of its simplicity, short administration time (10-15 min) and high predictive value.
Accommodation, Ocular↗
Selective deficit of visual search in moving displays after extrastriate damage.
A visual cue that is often associated with significant stimuli, such as those provided by prey and predators, is movement relative to the observer. An efficient visual system should be able to direct attention to those parts of the visual field that contain such stimuli. What is needed is a system that can filter by movement difference. This could direct attention to a moving item among stationary items, or an item moving in one direction against a background moving in a different direction. Visual search experiments have shown that people are indeed able to filter by movement; that is, they can attend to just the moving items in arrays of moving and stationary stimuli. Single-cell recordings from monkey visual cortex show that the medial temporal cortical area (MT) has some of the properties required to filter by movement. We have now linked these two observations by showing that a patient with bilateral lesions to the presumed human homologue of MT cannot restrict visual attention to the moving items in arrays of both moving and stationary items. This suggests that MT is the site of a movement filter used in normal visual processing.
Animals↗
The "motion-blind" patient: low-level spatial and temporal filters.
The "motion-blind" patient previously described by Zihl et al. (1983) was investigated using standard psychophysical procedures with stimuli whose spatial and temporal properties could be separately manipulated. Detection experiments for sinewave grating stimuli of varying spatial and temporal frequency showed sensitivity in this patient to be only slightly impaired. Temporal integration for stimuli of varying spatiotemporal frequency exhibited the expected space-time covariation seen in normal vision. An examination of the suprathreshold discriminative capacity of this patient was undertaken for spatial frequency, contrast, and temporal frequency. Although all of these discriminative functions were impaired, those concerning temporal frequency or velocity were dramatically reduced. No similar loss was seen for spatial frequency discrimination for moving or temporally varying stimuli. No measurable temporal frequency discrimination was present above 6 Hz and no velocity discrimination above 6 degrees/sec. Experiments involving the direction discrimination of suprathreshold drifting gratings of arrays of random dots revealed an inability to perceive direction of movement above a velocity of about 6 degrees/sec. Contrast thresholds contingent on direction of motion of a drifting grating also showed a much greater deficit than simple detection. Apparent motion using 2-flash random dot kinematograms revealed that the residual motion vision of this patient corresponded to the "short-range" motion process of normal vision. This process originally defined by Braddick (1974) operates over restricted space and time intervals. Apparent motion could only be supported by a narrow range of intermediate spatial displacements. These results suggest that this patient does exhibit some residual motion perception, probably corresponding to a severely impaired "short-range" mechanism. The patient's relatively intact ability to perform simple types of discrimination but severe impairment of performance at making judgments relevant to the nature of motion of the same stimuli suggests that while the components necessary for the analysis of motion are intact their more global associations have been disrupted. This implicates an extrastriate locus of the brain damage. Alternative explanations for the nature of the deficit are discussed.
Biomechanical Phenomena↗
The influence of homonymous visual field disorders on colour sorting performance in the FM 100-hue test.
An influence of visual field disorders on sorting performance in the FM 100-hue test is reported. Patients with left-sided field disorders performed worse in the conventional testing direction, i.e. from left to right, compared with patients with right-sided defects. Reversing the direction of sorting led, however, to a similar impairment in patients with right-sided field defects. Observations in normals tested under different conditions of hue sorting support the view that the difference obtained cannot be accounted for by a hemisphere difference in colour processing but by the strategy adopted by subjects.
Adolescent↗
[Homonymous hemianopsia and its rehabilitation].
The majority of patients with homonymous visual field disorders after postchiasmatic brain damage suffer from reading disabilities (known as hemianopic dyslexia) because the residual visual field is too small for complete comprehension of words and sentences. Furthermore, they typically show a reduction of searching movements in the affected hemifield. As a rule, an adequate adaptation of their reading and searching strategies to the field disorder does not take place spontaneously. Therefore, these patients need early and efficient systematic treatment. Using a new electronic device, both the impairments in reading and in visual exploration can be treated successfully within a relatively short period of time. Most of the patients successfully employ the strategies learned during training in their everyday lives. Thus, the proposed treatment may be considered an effective means of reducing the degree of their visual disability.
Attention↗
Plasticity and rigidity in the representation of the human visual field.
Neuronal plasticity in the mammalian visual system has been studied with a variety of experimental methods like induction of artificial squint and eye rotation. To investigate neuronal plasticity in the human visual system, we examined a patient with a congenital convergent squint of his left eye, who later suffered a vascular lesion in his left occipital lobe that led to an incomplete hemianopia in his right visual field. The examination revealed that the visual field representation in the striate cortex is rigidly prewired with reference to the anatomical fovea. In contrast, plasticity in the oculomotor system enables the patient to use a functional visual axis that does not correspond to the anatomical fovea. Local alterations of sensitivity within the visual field that indicate interactions among non-corresponding retinal points provide additional evidence of functional plasticity.
Esotropia↗
The influence of visual field disorders on visual identification tasks.
Visual identification of shapes, figures, objects and faces was tested in a group of 26 patients with homonymous field defects due to unilateral "posterior" brain damage. In addition, a search test was used for evaluation of the effect of visual field loss on visual information acquisition. Of the patients, 5 performed entirely normally, i.e. errorless and within age-matched time limits, in all tests. The majority of patients (n = 15) also performed correctly but required significantly more time than normals. In contrast, 6 patients showed a rather specific impairment in visual identification tasks. It is argued that visual field loss per se does not impair visual identification but may affect visual search and, thus, information acquisition. Visual identification may be impaired, however, if brain damage involves the inferotemporal cortex.
Adult↗
[Neglect: the phenomena of unilateral neglect following brain damage].
The term "neglect" designates various kinds of failure to orient or respond to or to report stimuli appearing at the side contralateral to a cerebral lesion. This failure cannot be explained by primary sensory or motor disorders. Essentially the following symptoms of neglect have been reported: inattention to visual (or) acoustical stimuli in one hemifield under unilateral and simultaneous bilateral presentation reduction in orienting responses (eye and head movements) to the neglected hemispace and deviation of head and gaze axes towards the intact hemispace omission or incomplete reproduction of one side of a figure of a text when copying or drawing from memory omission of one half of a well-known scene or picture when reporting from memory deviation of the egocentre as tested by visual, acoustic and somatesthetic stimuli towards the intact hemispace reduction of motor activities, especially for the extremities of one half of the body, which cannot be attributed to a sensory motor deficit inattention to somatesthetic stimuli presented on one side of the body displacement of somatesthetic stimuli, presented on the affected body side, to the intact body side lack of "awareness" of the existence of one half of the body, resulting in, e.g., ignoring this body half when washing or dressing "reference" of the neglected body half to another person unawareness or denial of severe sensorimotor deficits (e.g. hemiparesis) in the affected body half. The syndrome of neglect should be carefully differentiated from inattention phenomena resulting from primary sensory (e.g. hemianopia, restriction of field of search) and motor deficits (hemiparesis, hemiakinesis). In some cases this differentiation is rather difficult, because both types of inattention may be combined. Thus, detailed testing of sensory and motor disorders is needed in order to avoid any precipitate diagnosis of "neglect". The neuropathology of the neglect syndrome is not yet known precisely. Damage to the parietal lobe (presumably of the nondominant hemisphere) is the most common cause for neglect. Lesions at the bank of the sulcus intraparietalis seem especially crucial. Lesions in the dorsolateral frontal lobe causing neglect are mainly situated in Brodmann's premotor areas 8, 9 and 46. Furthermore, lesions of the anterior cingular cortex (area 24), of the thalamus (intralaminar nuclei, nucleus ventralis lateralis, pulvinar) and of the basal ganglia seem to induce neglect.
Attention↗
Visual field rehabilitation in the cortically blind?
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Blindness↗
Visual field recovery from scotoma in patients with postgeniculate damage. A review of 55 cases.
A group of 55 patients with homonymous field defects related to vascular or traumatic postgeniculate damage were trained by locating light targets presented within their blind field region. This systematic treatment led, in the majority of patients, to an enlargement of the visual field. Recovery depended on specific practice. Control experiments showed that field enlargement cannot be explained by eccentric fixation or perimetric measurement variability. It is hypothesized that recovery may take place at striate cortex level and may result from 'reactivation' of reversibly damaged nervous tissue. In cases that did not benefit from treatment, visual field loss may result from irreversible damage.
Adult↗
Visual performance and reading capacity of partially sighted persons in a rehabilitation center.
Visual acuity and reading performance of 178 partially sighted patients from a rehabilitation center were measured using a TV text display device. A linear relation was demonstrated between visual acuity and reading speed for patients with visual acuity values below 15% of the normal value. With respect to reading performance, three groups of partially sighted patients could be distinguished: (1) 25% of the patients are unable to read visually and require tactile reading aids; (2) 50% are partially sighted and require high-magnification electronic reading aids; (3) 25% can read normal text by using optical magnifying devices. There is evidence that reading performance is related to the nature of the underlying ocular problem, such as refractive anomalies, macular degeneration, or other diseases.
Adolescent↗
Lithium effects on ophthalmological-electrophysiological parameters in young healthy volunteers.
The effects of lithium on the visual system in man have been tested. Ten healthy volunteers followed a 10-day lithium regimen. Lithium plasma levels in the range of 0.6-0.8 mmol/l were obtained. Clinically used ophthalmological-electrophysiological tests were performed. Most of the tests showed no significant change during the lithium treatment. The lithium regimen resulted in a strong reduction of the slow phase. Also the "Arden-ratio", measured by electrooculogram (EOG), was influenced by lithium. The "Arden-ratio" reflects the corneo-fundal potential in retinal illumination and dark adaptation and is influenced by the state of adaptation. All the demonstrated effects were fully reversible at the end of lithium administration. Possible mechanisms of the action of lithium are discussed (for example Ca2+-fluxes, c-AMP, cGMP). These lithium-induced effects on the visual system in man may give some hint of the individual responsiveness to lithium.
Adult↗
Collicular function in human vision.
Threshold elevation in the periphery of the visual field as a consequence of repetitive stimulation can be abolished by stimulating a mirror-symmetric position in the contralateral visual half-field. A patient suffering from a congenital malformation of the right superior colliculus did not exhibit threshold elevation when stimulated repeatedly in the left visual field. Stimulation in the right visual half-field resulted in the usually observed threshold elevation, but stimulating a mirror-symmetric position in the left visual half-field did not abolish threshold elevation in the right half-field. These observations suggest that: (a) threshold elevation probably occurs as a consequence of collicular adaptation and (b) the mirror-symmetrically organized interhemispheric interaction is mediated at the collicular level.
Dominance, Cerebral↗