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PubMed1996

Visual evoked potential evidence for parallel processing of depth- and form-related information in human visual cortex.

This paper describes the first of two complementary studies designed to identify and to investigate the properties and likely functional significance of independently generated components of scalp-recorded responses evoked by stationary patterns. These experiments compared the influence of various stimulus parameters, including site of stimulation, pattern form, nature of background field and several binocular and monocular depth cues on a single subject's visual evoked potentials. The results revealed the presence, inter alia, of two topographically distinct components with the following properties. The earlier component (C2), whose polarity depends on the stimulus location in the visual field, is: contour-specific; best evoked by discrete pattern elements, but not gratings, in the central few degrees of the visual field; insensitive to any depth cues. By contrast, the later (consistently) negative potential (LNP) is not dependent on the form of the stimulus and is larger for paracentrally (beyond 1.5 degrees) than centrally located stimuli. It is also selectively enhanced by both monocular and binocular depth-cue stimuli, including the simulated forward movement of a pattern relative to a steady textured background; a stimulus which evokes no C2. The respective response properties of these scalp potentials suggest that there is parallel processing of depth- and contour-related features of stationary stimuli in anatomically separate regions of the human visual cortex.

Cues↗

PubMed1983

Perimetry, visual evoked potentials and visual evoked spectrum array in homonymous hemianopsia.

Confrontation field examination, perimetry, visual evoked potentials (VEPs) to pattern hemi-field stimulation and visual evoked spectrum array to flash stimulation were compared in 50 patients with homonymous hemianopsia. Visual field could be examined by confrontation in all patients and demonstrated the field defect in 96% of cases. Goldmann perimetry could only be performed in 60% of patients, but always quantitatively defined the margins of the defect. VEPs could only be tested in 77% of patients and demonstrated an abnormality in 79% of cases. VEPs were absent to stimulation of the affected hemifield in every case of homonymous field defects with macular splitting. Visual evoked spectrum array could be tested in 95% of patients and revealed abnormalities in 67% of cases. The relative value of each test is discussed.

Adult↗

PubMed2006

What determines sustained visual attention? The impact of distracter positions, task difficulty and visual fields compared.

We quantified the interference of distracter stimuli on sustained visuo-spatial attention as a function of the distribution of attended positions in the visual fields (bilateral/unilateral, left/right, upper/lower), distracter positions (peripheral, between attended positions, between fixation and attended positions) and task difficulty. Compared to distinct distracter positions, bilateral field and lower field presentation had much stronger influence on the performance. Additionally, interactive effects between task difficulty and distracter position were found. This result was at variance with the previous models of visuo-spatial attention, which attached much more importance to the role of distracter positions compared to visual field effects. In directly comparing the impact of the abovementioned factors, the converse finding is evident-visual field effects, in particular bilateral presentations have a much stronger importance. Moreover, metaphoric concepts of attention like the "zoom lens" are not compatible with these results. The findings are discussed in the light of alternative models of sustained visuo-spatial attention. The visual system architecture and top-down mechanisms are considered.

Adult↗

PubMed1999

Visual discrimination learning under switching procedure in visually deprived cats.

Previous studies have shown that fine visual discrimination learning is severely impaired in cats binocularly deprived in the early period of life (BD cats) and also somewhat in control cats reared with open eyes in the limited laboratory environment (C cats) compared with cats reared in a normal rural environment (N cats). It was concluded that visual deprivation impairs perceptual learning. In the present study discriminative stimuli were dissimilar and so the task was perceptually easy, but using a switching procedure made it associatively difficult. In regular trials a gate with a grating pattern was positive and a blank gate negative, whereas in switching trials the meaning of the gates was reversed. The switching stimulus was intermittent light in some stages of training and intermittent tone in others. Learning was severely impaired in BD cats and somewhat in C cats and the deficit was similar under visual and auditory switching. Thus, early visual deprivation impairs associative learning. The impairment probably includes associations between switching stimulus and instrumental responses and configural associations between switching stimulus and discriminative stimuli.

Animals↗

PubMed1989

Normal and abnormal visual development in kittens: insights into the mechanisms that underlie visual perceptual development in humans.

For many years the mechanisms that underlie normal and abnormal development of visual perception in human infants have been explored in anatomical and physiological studies on two species of frontal-eyed mammals, namely, cats and, to a lesser extent, monkeys. The unstated assumption underlying the investigations on cats is that despite substantial differences in the organization of the visual pathways of cats and humans, as well as quantitative differences in their perceptual abilities, principles of development established in the former also apply to humans. This review examines the extent to which this assumption may be valid. Following a review of certain anatomical peculiarities of the cat visual system, several of the differences as well as the parallels between the perceptual abilities of cats and humans are summarized. The latter similarities, as well as the larger number of parallels between the two species that can be drawn during development, attest to the validity of the choice of the cat for study of the mechanisms that underlie human visual development.

Animals↗

PubMed2004

Optical imaging of visually evoked responses in prosimian primates reveals conserved features of the middle temporal visual area.

Optical imaging of intrinsic cortical responses to visual stimuli was used to characterize the organization of the middle temporal visual area (MT) of a prosimian primate, the bush baby (Otolemur garnetti). Stimulation with moving gratings revealed a patchwork of oval-like domains in MT. These orientation domains could, in turn, be subdivided into zones selective to directional movements that were mainly orthogonal to the preferred orientation. Similar, but not identical, zones were activated by movements of random dots in the preferred direction. Orientation domains shifted in preference systematically either around a center to form pinwheels or as gradual linear shifts. Stimuli presented in different portions of the visual field demonstrated a global representation of visual space in MT. As optical imaging has revealed similar features in MT of New World monkeys, MT appears to have retained these basic features of organization for at least the 60 million years since the divergence of prosimian and simian primates.

Animals↗

PubMed1987

Pathology of the optic nerve and visual association areas. Information given by the flash and pattern visual evoked potential, and the temporal and spatial contrast sensitivity function.

Spatial and temporal contrast sensitivity functions (CSF) were compared with visual evoked potentials (VEP) in two groups of patients with pathology selectively affecting different parts of the visual pathway. These consisted of 10 patients with a selective delay of the pattern VEP due to demyelination of one optic nerve (unilateral optic neuritis) and 11 patients with a selective delay of the flash VEP due to pathology of the visual association areas (primary presenile dementia, or Alzheimer's disease). The results led to the following conclusions. Comparison of the VEP and CSF results indicated that VEP latency was more closely associated with the temporal CSF than the spatial CSF. Pathology of the visual association areas which selectively increased the latency of the flash P2 component also reduced sensitivity at low and medium temporal frequencies. In demyelination of the optic nerve, a highly significant correlation was found between the delay of the pattern reversal VEP and sensitivity at high temporal frequencies. Comparison of the results in these two types of pathology suggests that the pattern VEP and flash P1 component, the spatial CSF, and temporal CSF at high temporal frequencies are all processed in the geniculostriate pathway. The flash P2 component and temporal CSF at low and medium frequencies were affected differently from the other measures. The possibility that these processes are transmitted by nongeniculate pathways is discussed.

Adult↗

PubMed1986

Rabbit cingulate cortex: cytoarchitecture, physiological border with visual cortex, and afferent cortical connections of visual, motor, postsubicular, and intracingulate origin.

The connections of cingulate cortex with visual, motor, and parahippocampal cortices in the rabbit brain are evaluated by using a modified Brodmann cytoarchitectural scheme, electrophysiological mapping techniques, and the pathway tracers horseradish peroxidase (HRP) and tritiated amino acids. Rabbit cingulate cortex can be divided into areas 25, 24, and 29. Area 29 is of particular interest because area 29d has a lateral extension with a granular layer IV, area 29b has a caudal extension in which the connections differ from anterior area 29b, and there is a prominent area 29e. Cytoarchitectural delineation of the lateral border of area 29d with area 17 closely approximates the medial edge of the visual field representation in area 17 as determined electrophysiologically. The main interconnections between visual and cingulate cortices occur between cingulate areas 24b and 29d and visual areas 18 and medial parts of area 17. Projections between areas 29d and 18 are organized in a loose topographic fashion with rostral parts of each and caudal parts of each being reciprocally connected. Neurons mainly in superficial layer II-III of areas 17 and 18 project to layer I of area 29d, while the reciprocal projection originates from neurons in layer V of area 29d and project mainly to layer I of areas 17 and 18. The medial portion of motor area 8 projects to areas 18 and 29d and has a smaller projection to area 17. Postsubicular area 48 is reciprocally connected with area 29d, and it also projects to areas 29b and c. The subiculum projects to areas 29a and 29c but only to the anterior two-thirds of area 29b not the posterior one-third. Rostral area 29d receives the most extensive intrinsic cingulate projections including those from all major cytoarchitectural divisions. Interconnections between areas 29d and 29b appear to be topographically organized in the rostrocaudal plane. Area 29c projects more heavily to area 29b than vice versa. Finally area 29d projects mainly to area 24b in anterior cingulate cortex. In conclusion, rostral area 29d has extensive connections with visual areas 17 and 18, motor area 8, and all subdivisions of cingulate cortex. In light of these connections, it may play a pivotal role in associative functions of the rabbit cerebral cortex including visuomotor integration.

Animals↗

PubMed2006

Hypoperfusion of the visual pathway in parkinsonian patients with visual hallucinations.

Little is known about the developing mechanisms of visual hallucinations in Parkinson's disease. This study aimed to investigate perfusion changes in parkinsonian patients with visual hallucinations using n-isopropyl-p-[123I]iodoamphetamine ([123I]IMP) single photon emission computed tomography imaging. A total of 70 consecutive patients, including 31 patients with visual hallucinations, and 39 patients without hallucinations, participated in this study. Patients with severe cognitive impairment (Mini-Mental State Examination score < 20), nonvisual hallucinations, or confusion were excluded. We compared brain perfusion changes between the two groups. We found that hallucinatory patients had significant perfusion reductions in the bilateral inferior parietal lobule, inferior temporal gyrus, precuneus gyrus, and occipital cortex compared to nonhallucinatory patients. These results suggested that hypoperfusion of the visual pathway was closely related to visual hallucinations in Parkinson's disease.

Aged↗

PubMed1992

Plasticity of binocular visual connections in the frog, Xenopus laevis: reversibility of effects of early visual deprivation.

In frogs, each lobe of the midbrain optic tectum receives two spatially aligned maps of binocular visual space, one through each eye. The map from the contralateral eye is the product of direct retinal input to the tectum, while that from the ipsilateral eye is mediated by a commissural system of connections that relays binocular visual information from one tectal lobe to the other. In Xenopus laevis, dark-reared from early life, the visuotectal map through the ipsilateral eye exhibits significant signs of disorder indicating that the normal development of the underlying "intertectal" system involves experience-dependent processes. Here we investigate the potential of this system for recovery from such deprivation-induced disruption. Three groups of animals were first dark-reared from embryonic stages until 3 months, 12 months or 2 years after metamorphosis. These short-, medium- and long-term periods of visual deprivation are associated with a progressive disturbance of the intertectal system (Grant and Keating 1989b). The animals then experienced 12-18 months in a normal visual environment, before an electrophysiological mapping experiment was carried out to reveal the status of their intertectal system. Quantitative analyses of the visuotopic order in the ipsilateral visuotectal map and of its spatial alignment with the map derived from the contralateral eye revealed that these features were completely normal in all 3 experimental groups. It is concluded that defects present in the intertectal system of dark-reared Xenopus can be repaired by subsequent visual experience, and that the reparative capacity is not limited either by the animal's age or by the existing degree of prior disruption.

Animals↗

PubMed1990

Steady-state visually evoked potential topography associated with a visual vigilance task.

This paper describes data which demonstrate a correlation between the magnitude of the Steady-State Visually Evoked Potential (SSVEP) and visual vigilance. The SSVEP was recorded from 64 scalp sites and elicited by a 13Hz uniform visual flicker presented continuously while subjects undertook a visual vigilance task. Fifteen right-handed males were required to view three times a series of 180 geometrical shapes comprising a sequence of 60 squares, 60 circles and a further 60 squares. Each viewing of the 180 shapes constituted a trial. Trials 1 and 2 were identical while trial 3 differed from the first two in that one of the circles was modified. Subjects were ignorant as to the location of the modified circle and prior to the third trial, were challenged to identify the modified circle. A comparison of trials 2 and 3 indicated that the appearance of the modified circle was associated with an attenuation of the SSVEP in the occipito/parietal region. The same comparison indicated a pronounced SSVEP attenuation in the centro/parietal region during the interval that subjects were anticipating the appearance of the modified circle. These results suggest a distinction between the cortical activation patterns occurring during different phases of a visual vigilance task.

Adolescent↗

PubMed2006

Visual spatial clues enhance ocular torsion response during visual tilt.

Ocular torsion in response to a static tilt of a visual stimulus has been, and still remains in doubt. Furthermore, the possible underlying mechanism is not well understood. The authors' hypothesize that if the torsional response is related to the vestibular otolith system, then a visual stimulus with spatial clues important for maintaining body posture will induce a larger torsional response as compared to a stimulus lacking spatial information. Eye movements were recorded objectively in 15 healthy individuals using a 3D video oculography system. Three visual stimuli were used. In two tests, an identical photographic image of a city scene with spatial clues relevant for body posture were used, with the only difference being a square periphery in one stimulus (test 1) and a circular periphery in the other (test 2). The third stimulus (test 3) consisted of yellow rectangles on a black background with no natural spatial information. The scenes were tilted in 15 degrees steps from 0 degrees to 45 degrees in CCW and CW direction, and each position were held static for 15 s. All visual scene tilts induced a compensatory torsional response, which increased with stimuli angle. The stimuli with spatial clues induced more torsion compared to the stimulus without spatial clues. No difference was found when analysing the peripheral contour effect or direction of stimulus tilt. The present results support the hypothesis of an origin in the otolith system for the torsional response found to a static tilted visual scene.

Adolescent↗

PubMed1996

The effect of eye/head deviation and visual conflict on visually evoked postural responses.

Three interrelated experiments on visually evoked postural responses (VEPR) are presented to investigate the effect of lack of coplanarity between retinal and body coordinates (Experiment I) and the effect of directionally conflicting information in the visual stimulus. Experiment I showed that the direction of VEPR is modified by eye-in-orbit and head-on-trunk position signals, presumably of proprioceptive origin. Experiments II and III showed that VEPR can be critically suppressed by the presence of conflict within the visual stimulus (Experiment II: a linear, tangential component of visual motion acting in the opposite direction to the main angular component of a roll-motion display; Experiment III: a non congruent "improbable" visual motion parallax linear motion stimulus). A conceptual model of the postural system is presented, incorporating a gain control unit for the visuo-postural loop with inputs from the ocular/cervical proprioceptive system and from intra- and inter-sensory conflict detectors (comparators).

Adult↗

PubMed1992

Postnatal laminar development of cholinergic receptors, protein kinase C and dihydropyridine-sensitive calcium antagonist binding in rat visual cortex. Effect of visual deprivation.

The postnatal ontogeny of 3H-pirenzepine and 3H-oxotremorine-M binding to M1-and M2-muscarinic acetylcholine receptors, respectively, as well as 3H-nicotine binding to neuronal nicotinic acetylcholine receptors, 3H-phorbol-12,13-dibutyrate binding to protein kinase C and 3H-PN200-110 binding to dihydropyridine-sensitive calcium channels was studied in individual layers of the visual cortex in both normally raised and monocularly deprived rats (one eyelid sutured at the age of 11 days) using quantitative receptor autoradiography. Postnatal ontogeny of M1-muscarinic receptors is similar in each visual cortical layer reaching the highest receptor density at the age of 15 days, whereas M2-muscarinic binding sites increase gradually from day 7 up to day 34. Highest 3H-nicotine binding is reached in all visual cortical layers at postnatal day 15 followed by a considerable decrease in binding sites until day 25. Phorbol ester binding rises considerably from birth until the age of 15 days reaching nearly the adult value in the upper layers, whereas in layers V and VI a marked decrease in binding levels until adulthood can be observed. The developmental course of 3H-PN200-110 binding sites is similar in all visual cortical layers and exhibits a moderate rise in binding sites between postnatal days 7 and 15. Monocular deprivation results in permanent changes in the developmental profiles of phorbol ester as well as calcium antagonist binding sites, whereas the alterations in muscarinic and nicotinic cholinergic receptors following monocular deprivation are only of transient nature. The data presented suggest that acetylcholine plays a modulatory role during a certain period of early postnatal maturation of the visual cortex by affecting both cholinergic receptors and associated second messenger cascades.

Age Factors↗

PubMed2006

Visual performance of aspherical and spherical intraocular lenses: intraindividual comparison of visual acuity, contrast sensitivity, and higher-order aberrations.

PURPOSE: To intraindividually compare visual performance in terms of photopic high-contrast visual acuity (HCVA), mesopic HCVA, mesopic low-contrast visual acuity (LCVA), and contrast sensitivity (CS) in patients after implantation of either an aspherical or a spherical intraocular lens (IOL). SETTING: Department of Ophthalmology, Johann Wolfgang Goethe-University, Frankfurt am Main, Germany. METHODS: Forty eyes of 20 patients were randomized to implantation of an aspherical IOL (Tecnis Z9000, AMO) in 1 eye and a spherical IOL (Sensar AR40e, AMO) in the other eye. Three to 4 months postoperatively, photopic HCVA (270 cd/m(2)) was measured with the observer-independent Frankfurt-Freiburg Contrast and Acuity Test System (FF-CATS) and high-mesopic HCVA and LCVA (8 cd/m(2)) were measured with Early Treatment Diabetic Retinopathy Study charts. CS was assessed with the FF-CATS under photopic (167 cd/m(2)), high-mesopic (1.67 cd/m(2)), and low-mesopic (0.167 cd/m(2)) luminance conditions with and without glare. For each individual eye, higher-order wavefront aberrations were reconstructed for a physiological mesopic pupil diameter. Intraindividual differences (Delta(i)) in visual acuity, contrast sensitivity, and higher-order aberrations (HOAs) were calculated, and the influence of age and Delta(i) HOA on Delta(i) contrast sensitivity (logCS) under high-mesopic conditions was investigated using multiple regression analysis. RESULTS: There were no statistically significant differences between the Tecnis IOL and the Sensar IOL in visual acuity measurements or contrast sensitivity measurements. For physiological mesopic pupil diameter, primary spherical aberration (Z(4)(0)) was significantly lower in the Tecnis group (P<.001). For all parameters studied except Z(4)(0), the Delta(i) values were distributed around zero. Multiple regression analysis showed only a partial influence of Delta(i) Z(4)(0) on Delta(i) logCS (adjusted R(2) = 0.49) but did not show any influence of age, coma-like aberration, or residual HOA. CONCLUSIONS: Although Z(4)(0) was significantly lower in the eyes with the aspherical IOL, no statistically significant differences were found between aspherical and spherical IOLs in LCVA, HCVA, and contrast sensitivity. Statistical analysis of intraindividual contrast sensitivity differences showed that in most patients, this Z(4)(0) difference was too low to have an effect on contrast sensitivity.

Aged↗

PubMed2005

Decrease and increase in brain activity during visual perceptual priming: an fMRI study on similar but perceptually different complex visual scenes.

A robust finding among functional neuroimaging studies on visual priming is decreased neural activity in extrastriate and inferior prefrontal cortices for the second presentation of an object relative to its first presentation. This effect can also be observed for different but perceptually similar objects that are alternative exemplars of the initially presented object (e.g. two different pencils). An unanswered question is whether this decrease in activity can be found for the successive presentation of similar complex visual scenes. We used a test in which landscape pictures were divided vertically into three segments. A first segment was presented and followed several stimuli later by a second related segment. Reaction times were faster for the presentation of the second segment relative to the first one. Although perceptually different from the first segment, the presentation of the second segment was nonetheless associated with reduced activity in late stage visual processing areas including parahippocampal/fusiform gyri bilaterally, left middle occipital and temporal gyri, right inferior temporal and superior occipital gyri, and in left inferior frontal gyrus. The observed decreases in activity in these regions replicate results on priming of different exemplars of single objects while further extending these results to similar complex visual scenes. The presentation of the second segment was also associated with increased activity mainly in frontal and parietal regions, two areas known to be associated with memory retrieval. In sum, priming effects can also occur for complex visual scenes that are intrinsically different from each other although similar in their composition.

Adolescent↗

PubMed2002

Fomepizole therapy for reversal of visual impairment after methanol poisoning: a case documented by visual evoked potentials investigation.

PURPOSE: To illustrate the safety and efficacy of fomepizole in a case of methanol poisoning with initial visual impairment. DESIGN: Interventional case report. METHODS: A 60-year-old man was admitted with blurred vision and changes in color perception 18 hours after ingesting 100 ml methanol. Fomepizole was chosen for antidotal therapy in combination with hemodialysis. Flash electroretinogram (fERG) and flash visual evoked potentials (fVEPs) examinations were obtained at the bedside 2 hours after admission and on days 1 and 8. The monocular pattern-reversal visual evoked potentials (pVEPs) were investigated on days 1 and 8. RESULTS: A complete reversal of visual impairment was achieved within 20 hours. An abnormal b-wave amplitude and an increased peak III latency at VEPs were present on admission and recovered within 24 hours. CONCLUSIONS: Fomepizole appeared safe and effective for a patient who had severe methanol poisoning presenting with visual impairment.

Alcohol Dehydrogenase↗

PubMed1998

The role of the corpus callosum in visual orienting: importance of interhemispheric visual transfer.

In a tachistoscopic visual search task, the effects of ipsi- and contralateral distractors on target search were investigated in two complete commissurotomy patients. Pop-out distractors slowed the search for contralateral targets in both patients, i.e. search was not independent in both hemifields. In normals, we previously observed an extinction-like asymmetry in that distractors in the right visual hemifield interfered with target search in the left visual hemifield, but not vice versa. This pattern was also found in one of our patients, N.G., whereas the other, L.B., showed a reversed laterality effect. While N.G. is able to transfer visual shape information between hemispheres, L.B. is not. The data suggest that the reversal of the contralateral distractor asymmetry in L.B. is due to the disruption of ipsilateral visual input to the right hemisphere.

Corpus Callosum↗