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Results for “Evoked Potentials, Visual”

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At least 631 records · Page 35Linked to original sources

PubMed1988

Visual evoked potentials in the investigation of "blindsight".

We recorded long-latency visual evoked potentials in four patients with homonymous hemianopias, one of whom had clinical evidence of "blindsight." Stimuli consisted of different words that appeared randomly and at a constant angle to either side of the center of a TV screen, and subjects responded to one previously specified word (the "target") by finger extension. Target stimuli in the intact hemifield elicited a well-formed P3 response in all subjects, whereas stimuli in the blind field produced no such response except in the subject with blindsight. In addition, the earlier potentials in this subject were larger with stimulation of the blind hemifield than the intact field. By contrast, a P100 response was present only with stimulation of the intact field in this subject. These results indicate that cognitive processing of visual stimuli can occur even when subjective awareness of such stimuli is absent, and suggest that such processing occurs independently of the geniculostriate pathway.

Adult↗

PubMed2005

The visual evoked potential in the mouse--origins and response characteristics.

The visual evoked potential (VEP) in the mouse is characterized and compared to responses obtained with the electroretinogram (ERG). The results indicate that: 1, the VEP originates in the visual cortex; 2, the rod and cone pathways contribute separately to the VEP; 3, temporal tuning functions for rod and cone ERGs are low pass and band pass, respectively; VEP tuning functions are both band pass; and 4, VEP acuity is 0.62+/-0.156 cycles/degree. The differences in the spatial and temporal tuning functions obtained from the retina and visual cortex provides a tool to investigate signal processing through the visual system.

Adaptation, Ocular↗

PubMed1987

Contrast sensitivity and pattern visual evoked potential in patients with glaucoma.

Contrast sensitivity and pattern visual evoked potential (VEP) were measured in cases of ocular hypertension and primary open-angle glaucoma at various stages. The visual field of each eye was examined quantitatively and the retinal nerve fiber layer and optic disc were precisely assessed with magnified stereoscope fundus photography. This study revealed that contrast sensitivity of the eyes with glaucoma was within the normal range in the very early stage of the disease. As optic nerve damage advanced, high- or low-frequency loss developed. Further optic nerve damage produced a level type of loss. Pattern VEPs also showed increasing abnormalities as glaucomatous optic nerve damage progressed. Measurements of contrast sensitivity and pattern VEP were found not to be as sensitive as quantified precise visual field measurement or color stereoscopic fundus photography for detection of minor optic nerve damage in cases of early glaucoma. These methods may be useful, however, as an objective and subjective monitor of progression of optic nerve damage in glaucoma.

Adolescent↗

PubMed2005

Hyperglycemia with occipital seizures: images and visual evoked potentials.

PURPOSE: Hyperglycemia may rarely be seen with visual seizures. Observation of both visual evoked potentials (VEPs) and magnetic resonance imaging (MRI) in visual status epilepticus (SE) has not been reported. We describe acute and follow-up VEP and MRI findings of a patient with hyperglycemia-related visual SE of occipital origin. METHODS: In a 59-year-old diabetic woman, complex visual hallucinations and illusions developed with < or =10 seizures per hour as an initial manifestation of nonketotic hyperglycemia. RESULTS: Neurologic examination revealed ictal nystagmus to the right and continuous right hemianopsia. Ictal electroencephalography (EEG) and Tc-99m hexamethylpropylene amine oxime (HMPAO) single-photon emission computed tomography (SPECT) revealed an epileptogenic focus in the left occipital lobe. MRI with fluid-attenuated inversion recovery showed focal subcortical hypointensity and gyral hyperintensity. Follow-up MRI showed only minimal gyral hyperintensity at 6 months. The P100 amplitude of VEP was significantly higher at the right occipital area during SE, but slightly higher on the left after the patient had been seizure free for 6 months. CONCLUSIONS: Occipital seizures and hemianopsia can be caused by hyperglycemia and may be accompanied by special MRI and VEP findings.

Electroencephalography↗

PubMed1983

Abnormalities of visual evoked potentials by checkerboards in children with specific reading disability.

Visual evoked potentials by checkerboards of varying check sizes were recorded in the two hemispheres of 16 specific reading disabled and 8 normal children. In most of the disabled subjects a gross hemisphere asymmetry was assessed, while in the control group the usual evoked potential symmetry was observed. In some disabled subjects the evoked potentials had a larger amplitude in the right hemisphere, while in others the amplitude was larger in the left hemisphere. In a small subgroup the evoked potentials were symmetrical, but they had a smaller amplitude than in the control subjects. The results, giving evidence of a dysfunction in basic visual processing, are discussed in the context of current literature on clinical subgroups and the interhemispheric relationship in the dyslexic syndrome.

Child↗

PubMed2003

The pattern-pulse multifocal visual evoked potential.

PURPOSE: To define the pattern-pulse multifocal visual evoked potential (PPMVEP) and determine its characteristics in a sample of normal subjects in terms of amplitude of response attainable, the variation in waveform across visual field, and distribution of potential over the scalp and to compare pattern-pulse with contrast-reversal multifocal stimuli. METHODS: VEPs were obtained by concurrently stimulating 60 regions of a cortically scaled dartboard with pulses of pattern contrast. Responses were recorded from normal subjects, by using a 32-channel electroencephalogram recording system, and elementary responses to each region were estimated by multiple regression of each of the response channel signals on stimulus signals. Left-eye, right-eye, and binocular viewing conditions were concurrently tested by dichoptic stimulation. A direct comparison was then made with contrast-reversal stimulation. RESULTS: Response waveform sets for 12 subjects varied in maximum amplitude from 1.8 to 6.8 micro V. A stereotypical distribution of waveforms held in most subjects, depending primarily on the polar angle location of the stimulus within the visual field. In a direct comparison with a contrast-reversal multifocal analysis, the pattern-pulse responses had similar waveforms and scalp topography, but were 15 times larger in amplitude. Root mean square (RMS) signal-to-noise ratio (SNR) was 1.9 times higher with pattern-pulse stimulation, corresponding to a reduction of 73% in recording time to achieve the same SNR. CONCLUSIONS: The PPMVEP can simultaneously characterize 60 regions of the visual field for both eyes in less than 7 minutes. A general methodology is illustrated that allows multifocal analysis with flexible choice of stimulus conditions.

Adult↗

PubMed1991

Visual dysfunction in treated schizophrenia suggested by visual evoked potentials from pattern-reversal stimulation.

Steady-state visual evoked potentials (steady-state VEPs) from pattern-reversal stimulations were compared in treated schizophrenic patients and normal subjects matched for sex and age. The VEP amplitudes were more variable in the patients than in the controls. Furthermore, the VEP amplitudes of the patients mostly showed little or no change when the check size was varied, in contrast to the controls who showed a marked check size effect. These results suggest that schizophrenics receiving drugs have dysfunction of the visual system, especially an inability to respond adequately to changes of visual information.

Adult↗

PubMed2006

The VESPA: a method for the rapid estimation of a visual evoked potential.

Faster and less obtrusive means for measuring a Visual Evoked Potential would be valuable in clinical testing and basic neuroscience research. This study presents a method for accomplishing this by smoothly modulating the luminance of a visual stimulus using a stochastic process. Despite its visually unobtrusive nature, the rich statistical structure of the stimulus enables rapid estimation of the visual system's impulse response. The profile of these responses, which we call VESPAs, correlates with standard VEPs, with r=0.91, p<10(-28) for the group average. The time taken to obtain a VESPA with a given signal-to-noise ratio compares favorably to that required to obtain a VEP with a similar level of certainty. Additionally, we show that VESPA responses to two independent stimuli can be obtained simultaneously, which could drastically reduce the time required to collect responses to multiple stimuli. The new method appears to provide a useful alternative to standard VEP methods, and to have potential application both in clinical practice and to the study of sensory and perceptual functions.

Adult↗

PubMedDate not supplied

Electroretinogram and visual-evoked potentials in children with optic nerve coloboma.

The aim was to evaluate alterations in Visual-Evoked Potentials (VEP) and Electroretinogram (ERG) and discover whether these tests are useful for determining residual visual acuity in cases where a patient is unable to collaborate. Flash and, when possible, Transient Pattern Reversal Visual-Evoked Potentials and Maximal Response ERG were recorded in 8 children (under three years old) affected by different aspects of optic nerve coloboma. None of them had visual acuity evaluated because of poor collaboration. All examinations were carried out using skin electrodes. Amplitude of the a and b component of ERG, amplitude, morphology and latency of the major components of Flash VEP and amplitude and latency of P100 Pattern Reversal VEP were evaluated. Four of the patients were examined three years later and visual acuity was compared with the previous electrofunctional results. Alterations in ERG were found only in the case of significant retinal anomalies (great coloboma, retinal detachment), huge alterations were found in both Flash VEP and in Pattern Reversal VEP. The retrospective study of VEP traces and visual acuity showed a good correlation between electrofunctional data and visual capability. Electrofucntional examinations can identify important conductive retinocortical anomalies. The possibility of correlating electrophysiological results with residual visual acuity is important for rehabilitative management in such optic disc malformations.

Child, Preschool↗

PubMed1976

[The alteration of visual evoked potentials in light- and dark-adapted states as a measure for the visual field sensibility at elevated intraocular pressure (author's transl)].

On 12 voluntary subjects with normal visual function the intraocular pressure was increased dependent on the ophthalmic blood pressure Pm = (Ps + Pd)/2. The visual field was tested under this pressure load by means of a subjective method and the visual evoked potential was derived under light and dark adaptation. Comparison of subjective and objective investigations demonstrated that the different visual evoked potentials which are dependent on the state of adaptation are a measure for the pressure sensibility of prelaminar optic nerve fibers.

Adaptation, Ocular↗

PubMed1992

Comparative effects of luminance and scatter on the pattern visual evoked potential and eye-hand reaction time.

We investigated the effect of reduced luminance and increased scatter on the pattern visual evoked potential and eye-hand reaction time evoked to a check size of 0.5 degrees in 10 normal subjects. Data analysis indicated that a reduction in luminance as well as an increase in scatter caused a statistically significant increase in the peak time of the pattern visual evoked potential P100 wave. The reaction time, however, was not significantly affected by the initial 0.9-log unit attenuation of the stimulus luminance or the 0.3 scatter filter. Further attenuation of luminance or increase of scatter also yielded statistically significant increases. Our results suggest that the reaction time is less affected by a reduction in luminance or an increase in scatter of a 0.5 degrees stimulus than the pattern visual evoked potential is and therefore represents a more reliable test to assess visual function, especially in the presence of medial opacities, which are known to reduce luminance and produce scatter.

Adolescent↗

PubMed1999

Study of visual evoked potentials during normal monthly cycle in normal female subjects.

Visual Evoked potential (VEP) is one of the electrophysiological technique which is used by Neurologist and Ophthalmologist for better diagnosis of optic nerve fiber and visual cortex diseases such as Multiple Sclerosis, Optical neuritis and etc. Among the female patients used to contact the Qods electrophysiological laboratory, the authors observed the extraordinary changes in VEP pattern, which was not expected by authors, hence the research was carried out to see the possible causes of such changes. One of the trails was the physiological monthly cycle and it's possible effect on VEP pattern. For this purpose 20 normal female subjects in age group between 18-28 years were selected and they undergone VEP recording in one of ordinary and monthly cycle days, both with checkerboard pattern reversal as well as flash stimulation. The results is a proof for the changes in latency of P100 peak and the shape of VEP pattern which is reflecting more in flash than pattern reversal stimulation. Finally it is suggested to related medical specialist to take into consideration the effect of monthly cycle in recording VEP in female subject.

Adolescent↗

PubMed1995

[Pattern-reversal visual evoked potentials dissociated vertical deviation].

We recorded pattern-reversal visual evoked potentials (P-VEP) from dissociated vertical deviation (DVD) patients to evaluate the sensory system abnormalities in DVD. 91 DVD patients with good visual acuity were studied. Normal subjects and horizontal strabismic patients without DVD were compared for evaluation. Transient and steady state P-VEPs were recorded from three EEG electrodes placed on the posterior scalp. Half-field checker-board reversal stimulation was applied to stimulate monocular temporal retina and responses from right and left hemispheres were also compared for evaluation. Paradoxical lateralization was observed in all normal subjects. Abnormal P-VEPs were observed in 4 of 20 (20%) horizontal strabismic patients without DVD when employing the transient stimulation method and in 2 of 8 (25%) when using steady state stimulation. Abnormal P-VEPs were observed in 31 of 67 (46.3%) DVD patients, with the transient stimulation method and in 20 of 25 (80.0%) DVD patients with the steady state stimulation method. The abnormalities were various and diverse. Our observations indicate that DVD patients frequently have an abnormal sensory system detected by P-VEP, and DVD might be a complex and multi-origin condition involving both sensory and motor systems.

Adolescent↗

PubMed1984

Visual evoked potentials in a rabbit model of hepatic encephalopathy. I. Sequential changes and comparisons with drug-induced comas.

The recording of visual evoked potentials in rabbits has been shown to be an objective, reproducible, noninvasive technique for quantitating changes in the pattern of cerebral neuronal activity. The development of hepatic encephalopathy due to galactosamine-induced fulminant hepatic failure was consistently associated with a series of distinctive changes in the visual evoked potential waveform. The pattern of the visual evoked potential in hepatic coma (due to galactosamine-induced fulminant hepatic failure) differed fundamentally from that in ether-induced coma, but was identical to that in comas induced by three drugs which activate gamma-aminobutyric acid-ergic neural mechanisms: pentobarbital, diazepam, and muscimol. These findings are compatible with activation of the gamma-aminobutyric acid inhibitory neurotransmitter system contributing to cerebral neuronal inhibition in hepatic coma due to galactosamine-induced fulminant hepatic failure.

Animals↗

PubMed1980

[Optic nerve involvement in neuro-syphilis: diagnostic evaluation by pattern-reversal visual evoked potentials (VEP) (author's transl)].

Pattern-reversal visual evoked potentials (VEP) were recorded in 41 patients suffering from syphilis in different stages. --In a latent syphilis 3 from 50 eyes (6%) had abnormal VEPs although ophthalmological findings were normal. --In neuro-syphilis, however, 16 from 32 eyes (50%) showed delayed responses. Ophthalmological findings were much less abnormal: visual acuity in 12%, visual field in 19%, and either or both of them in 25%. Pupillary disturbances were observed in 62%.

Evoked Potentials↗

PubMed1981

Pattern reversal visual evoked potentials. Studies in Charcot-Marie-Tooth hereditary neuropathy.

Pattern reversal visual evoked potentials (PRVEP) were studied in 25 patients from 17 separate families with Charcot-Marie-Tooth (CMT) syndrome. Twenty patients had classic CMT with depressed tendon reflexes, slow motor nerve conduction velocities, and autosomal dominant inheritance. Four patients demonstrated typical findings of CMT, but there was no documented family history. One patient had the axonal form of hereditary motor sensory neuropathy. Abnormally delayed latencies of the PRVEP were found in four patients (16% of the total), including the only patient with clinical optic atrophy. There was no consistent correlation, of PRVEP with severity of disease. These results confirm earlier clinical reports of occasional optic nerve involvement in CMT and represent additional evidence that central pathways may be involved in this primarily peripheral nervous system disorder.

Adolescent↗

PubMed1989

Pattern visual evoked potentials and pattern electroretinograms in hypothyroidism.

This study reports the pattern visual evoked potential (PVEP) findings in 10 patients with idiopathic hypothyroidism. Eight of these patients also had pattern electroretinography (PERG) performed and six were additionally seen after treatment with thyroxine. Only one patient had definitely abnormal PVEPs at the time of initial recording. PERGs at this time were of abnormal latency and subnormal amplitude. Following treatment with thyroxine the patient became euthyroid. Repeat electrodiagnostic testing now showed both PERGs and PVEPs within the normal range, having markedly improved in both latency and amplitude. This suggests that the PVEP delay was probably secondary to reversible central retinal dysfunction.

Electroretinography↗

PubMed1993

Dose dependent effects of alcohol on visual evoked potentials.

The effects of various alcohol doses on components of the visual evoked potential were investigated. Using a repeated measures, Latin square design, five alcohol dose conditions were administered to ten male subjects: 0.00 (placebo); 0.28; 0.36; 0.54 and 0.72 g/kg total body weight. EEG responses to a reversing checker board stimulus were measured in a standard oddball paradigm. In the alcohol conditions, latencies of the P1 and P2 components of the VEP were unaffected. However, reaction time, and the latencies of N2 and P3 displayed significant dose related increases with increasing blood alcohol levels. Further, RMS power of the P3 complex was reduced by higher alcohol doses, as was the N2-P3 amplitude difference at central and parietal sites. It is concluded that the latency and power of the endogenous components of the VEP are altered by alcohol, without effects being seen in earlier components.

Adolescent↗