PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Evoked Potentials, Visual”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 487 records · Page 27Linked to original sources
PubMedDate not supplied

Spatial neglect is associated with increased latencies of visual evoked potentials.

We have recorded steady-state visual evoked potentials (VEPs) from patients with vascular damage to their right brain hemispheres, some suffering from unilateral spatial neglect (n = 9), and some not (n = 7). VEPs were recorded in response to sinusoidal gratings of 0.56 cycle/deg contrast-reversed sinusoidally at temporal frequencies from 4-11 Hz. Stimuli were presented either to the left or to the right visual field, or to both. Confirming previous reports, reliable VEPs were recorded from stimuli in the left contralesional hemifield, of comparable amplitude to those of the ipsilesional hemifield and to those of both hemifields of brain damaged patients without neglect. However, analysis of apparent latency derived from phase data showed that the VEPs from the contralesional hemifield were systematically delayed by 30-40 ms compared with those of the ipsilesional hemifield, and compared with both hemifields of the nonneglect groups. This result suggests changes in neural processing in neglect patients.

Adult↗
PubMedDate not supplied

Monocular contribution to the peak time of the binocular pattern visual evoked potential.

The contribution of each monocular pathway to the timing of the binocular pattern visual evoked potential was assessed in situations where a significant interocular timing discrepancy was observed. Monocular and binocular pattern visual evoked potentials to 0.5 degree checks were recorded from normal subjects, normal subjects in whom one eye was blurred, patients with monocular amblyopia, and patients with resolved unilateral optic neuritis. Normal subjects showed facilitation, while suppression was evidenced in subjects with monocular blurring. In patients with amblyopia, the affected pathway had no effect on binocular pattern visual evoked potential latency, suggesting that the amblyopic eye was suppressed. In contrast, all patients with optic neuritis showed binocular averaging. Our results show that different forms of binocular interaction are evidenced in normal subjects, in amblyopia and in optic neuritis, and suggest that a comparative analysis of monocular and binocular pattern visual evoked potential peak times brings valuable information to the clinical evaluation that could be used to distinguish disease processes further.

Adolescent↗
PubMedDate not supplied

Effect of spatial frequency on simultaneous recorded steady-state pattern electroretinograms and visual evoked potentials.

Pattern electroretinograms (P-ERGs) and visual evoked potentials (VEPs) to 4 Hz alternating square-wave gratings were simultaneously recorded in 23 subjects. Responses were Fourier analyzed and amplitude and phase of the 2nd and 4th temporal harmonics were measured. The spatial frequency-amplitude function of the P-ERG 2nd harmonic component displayed either a bandpass tuning behavior, or a low-pass behavior. The peak amplitude for subjects with bandpass tuning was at 1.5 c/deg. The phase of the P-ERG 2nd harmonic decreased monotonically as spatial frequency increased. The VEP 2nd harmonic had a bimodal spatial frequency function with a peak at 3 c/deg and a second increase at spatial frequencies below 1 c/deg, regardless of the P-ERG characteristics. The phase of VEP 2nd and 4th harmonic had an inverted U-shaped function with peak at 3 c/deg and 1.5 c/deg respectively. Comparison of simultaneously recorded P-ERG and VEP spatial frequency functions demonstrated different tuning behavior for cortical and retinal responses. It is concluded that the proposed technique permits the separate analysis of retinal and cortical processing of visual information. The 2nd and 4th harmonic components of bEP behave independently of each other suggesting they may be generated by different subsystems.

Electroretinography↗
PubMed1991

Saccade onset and offset lambda waves: relation to pattern movement visually evoked potentials.

The lambda (lambda) wave is an occipital EEG potential which occurs when saccadic eye movements are made against an illuminated contrast background. There is some disagreement concerning the presence of sub-components to the lambda-wave, and its relationship to visually evoked potentials. In the present study, lambda-waves were recorded with saccades of different durations (30-110 ms) and compared to VEPs associated with pattern movements of similar durations and velocity. It was found that the lambda-wave consisted of a saccade onset component with positive sub-components at 59 and 100 ms after saccade onset, and a saccade offset component with a positive potential at 74 ms after saccade offset. With small saccades of 30 ms duration or less, these components superimposed to form a single lambda-wave. In the case of pattern movement VEPs, a movement onset component of latency 110 ms following movement onset, and a movement offset component at 89 ms after movement offset, were identified. The similar behaviour of the lambda-wave and VEP under these conditions supports the view that the lambda-wave is a visually evoked potential resulting from movement of the visual field across the retina during a saccadic eye movement.

Adult↗
PubMed1979

[Emitted cerebral activity and attention processes in a group of schizophrenic methodologic problems].

This is a study of the relationship between cerebral events and visual attentional processes of schizophrenic patients by means of a spectral analysis method described in this paper. With recorded data it is possible to study the EEG, standard visual evoked potential, visual evoked potention with attention and visual 'emitted' potentials when stimuli were expected but absent. Compared with the summation method and unitary analysis, the spectral analysis method appears very interesting, especially for the study of 'emitted' potentials because it avoids the subjectivity of operators and reduces the number of stimulations. The results show the interest of this simple reliable and effective method for the detection and objectivation of evoked activities with only very few (10) stimulations.

Attention↗
PubMed2006

Prevalence of abnormal pattern reversal visual evoked potentials in craniosynostosis.

BACKGROUND: The purpose of this study was to examine the prevalence and type of changes observed in the pattern reversal visual evoked potentials recorded at the first assessment of children with craniosynostosis. METHODS: Visual evoked potentials were recorded from 114 patients with craniosynostosis. Eighty-one patients were syndromic and 33 were nonsyndromic. No patient had received any craniofacial surgical intervention. At the time of the test, 22 of 40 patients were aged 6 months and younger, and 18 patients were between 6 months and 1 year of age. Pattern reversal visual evoked potentials were recorded from a midoccipital electrode positioned 3 cm above the inion. The pattern reversal visual evoked potentials elicited to 50' checks with three reversals per second viewed with both eyes were analyzed for n80-p100 amplitude, p100 latency, and breadth of waveform. RESULTS: Sixty percent of patients had abnormal pattern reversal visual evoked potentials to 50' checks. This did not show a significant association with age, or classification of craniosynostosis. CONCLUSIONS: The high prevalence of abnormal pattern reversal visual evoked potentials to a robust stimulus suggests that visual pathway dysfunction, as measured electrophysiologically, can affect a majority of patients with craniosynostosis. This study indicates that a baseline evaluation of all children with craniosynostosis at their first presentation is essential if subsequent electrophysiologic visual pathway monitoring is to take place.

Craniosynostoses↗
PubMed2002

Pattern-reversal visual evoked potentials in infants: gender differences during early visual maturation.

This paper investigates gender differences in the peak latency and amplitude of the P1 component of the pattern-reversal visual evoked potential (pattern-reversal VEP) recorded in healthy term infants. Pattern-reversal VEPs in response to a series of high contrast black and white checks (check widths 120', 60', 30', 24', 12', 6') were recorded in 50 infants (20 males, 30 females) at 50 weeks post-conceptional age (PCA) and in 49 infants (22 males, 27 females) at 66 weeks PCA. Peak latency of the major component, P1, was considerably shorter in female compared with male infants. Differences in head circumference do not entirely account for the gender differences in peak latency reported here. A gender difference in P1 amplitude was not detected. These findings stress the importance of considering gender norms as well as age-matched norms when utilizing the pattern-reversal VEP in clinical investigations. Studies including a wider range of ages are clearly necessary in order to establish whether the earlier peak latencies in female infants represents a difference in the onset or rate of visual maturation.

Age Factors↗
PubMed1989

Nonlinearities in binocular visual evoked potentials in children.

Evidence is controversial in respect to the optimal conditions in which visual evoked potentials provide an objective measure of binocular visual function, related and unrelated to stereopsis, and there is little emphasis on the type of stimulus that produces facilitation in binocular recording. We investigated the effects of stimulus type (flicker or pattern), contrast, and temporal modulation on facilitation, which was defined as a binocular response greater than sum of monocular responses. Monocular and binocular responses to sinusoidally modulated flicker and grating patterns were recorded in children and Fourier analyzed. The relationship of the fundamental Fourier component for flicker and the second harmonic component for pattern were each examined as function of temporal modulation at two levels of contrast for monocular and binocular visual evoked potentials. Binocular facilitation was found across all conditions for flicker. Data suggest that processing of pattern and flicker has different sites of origin within the visual system. Facilitation in binocular visual evoked potentials also indicates that they are not a result of simple summation of monocular responses, since there appears a nonlinear component to such interaction.

Analysis of Variance↗
PubMed1996

Follow-up studies on the usefulness of the flash visual evoked potential.

Thirty patients with possible demyelinating disease or visual system disorder were referred for Visual Evoked Potentials (VEP) and had abnormal flash (FL) but normal pattern reversal (PR) responses. Patients with confirmed organic brain disorders had significantly longer latencies to P100 from FL than in the unconfirmed group, but the subgroup, later proven to have demyelinating disease had the most significantly abnormal latencies to FL. Even the PR responses, although within normal limits, showed significantly longer latencies in the organic brain disorder group, compared to the unconfirmed group. For patients who could be followed-up, 45% of them proved to have demyelinating disease. A visual disorder was confirmed in 53% and an organic brain disorder in an additional 13%, so that 2/3 of all patients had one of the latter two conditions. These data argue for the use of flash, in addition to the pattern reversal stimulus, in the protocol for visual evoked potentials.

Demyelinating Diseases↗
PubMed1990

The visual evoked potential in clinical hepatic encephalopathy in acute and chronic liver disease.

Flash visual evoked potentials were measured in 19 patients with chronic liver disease and in 19 patients with acute hepatic damage secondary to paracetamol overdose with and without clinical hepatic encephalopathy. The flash visual evoked potential showed a series of changes which correlated with the clinical grade and the delta activity of the electroencephalogram in chronic liver disease, and with the delta activity of the electroencephalogram but not with the clinical grade in acute hepatic damage. The changes observed in the flash visual evoked potential in the encephalopathy of chronic liver disease were different from those seen in the corresponding clinical grade of acute hepatic damage, suggesting different pathogenetic mechanisms for encephalopathy in these two conditions.

Acute Disease↗
PubMed1988

Anatomy and physiology of visual evoked potentials and electroretinograms.

ERGs are electrical potentials originating in the retina and recorded directly from the corneal surface of the eyes. Flash ERGs are elicited by high intensity flashes either on scotopic or photopic conditions. The origin of the A and B waves of ERG are a combination of photoreceptor potentials, K+ mediated current flow and DC potentials within Müller cells, whereas the C waves are altered K+ fluxes induced by light in the pigment epithelia. Oscillatory potentials are probably related to feedback circuits of the inner layer of the retina. Electroretinograms evoked by pattern are mostly originated in ganglion cells. The use of various visual stimuli allow the selective activation of different retinal structures. Flashes selectively activate retina luminance and color detectors, whereas small pattern stimuli preferentially activate contrast and edge detectors. Visual evoked potentials recorded from the scalp probably originate from multiple cortical visual areas. P-100 response of the visual evoked potential to pattern stimulation is a cortically originated wave either produced exclusively by area 17 or 18 or by a multiplicity of cortical neuronal pools. Visual evoked potentials have important application for the diagnosis of optic nerve disease, assessment in conjunction with pattern ERG of the prognosis of recovery of visual function, and the evaluation of visual physiology and physiopathology.

Animals↗
PubMed1989

Visual evoked potential processing under acceleration stress.

A study of the use of visual evoked potentials to detect acceleration induced blackout is presented. Decisions concerning the presence or absence of the visual evoked potential within the measured EEG were made using detection and estimation-based approaches. The performance of each technique is evaluated in two ways: (a) via a performance index (PI) which is introduced in this work, and (b) by the accuracy of pure detection. Variations of the main processing techniques such as output averaging and decision thresholding were also investigated.

Acceleration↗
PubMed1989

The visual evoked potentials and the spatial vision in old people.

The latency of the visual evoked potentials elicited by pattern-reversal and onset-offset stimulation was measured in 75 healthy subjects aged 21 to 80 years. In 24 of these subjects the contrast sensitivity threshold was recorded by electrofunctional method. There is a close correlation between increasing latency of visual evoked potentials and age increase. This finding is of greater importance after 60 years. The delayed latencies are obtained with both pattern-reversal and onset-offset stimulation, and are more striking using stimuli of small size. In the old people the contrast sensitivity shows a raised threshold, especially for small stimuli. These age-related changes of the visual evoked potentials and contrast sensitivity are due to optical factors--the most important is the reduction of the retinal illuminance caused by senile miosis--and to neural factors as degeneration and demyelination of the optic nerve axons and abnormalities of the neurotransmitters.

Adult↗
PubMed1994

The pattern visual evoked potential. A multicenter study using standardized techniques.

The peak latency of the pattern-reversal visual evoked potential is a sensitive measure of conduction delay in the optic nerve caused by demyelination. Despite its clinical utility, the pattern-reversal visual evoked potential has not previously been used in multicenter clinical trials, presumably because of difficulty in standardizing conditions between centers. To establish whether the pattern-reversal visual evoked potential could be adequately standardized for use as a measure in multicenter therapeutic trials for optic neuropathy or multiple sclerosis, stimulus and recording variables were equated at four centers and pattern-reversal visual evoked potentials were recorded from 64 normal subjects and 15 patients with resolved optic neuritis. Results showed equivalent latency and amplitude data from all centers, suggesting that stimulus and recording variables can be satisfactorily standardized for multicenter clinical trials. N70 and P100 peak latencies and N70-P100 interocular amplitude difference were sensitive measures of resolved optic neuritis.

Adolescent↗
PubMed1985

Rapid contrast sweeping of steady-state visual evoked potentials: a new method for investigation of the visual system.

Rapid sweeping of contrast modulates the steady-state visual evoked potentials (VEP) obtained by sinusoidal gratings reversing at 16 Hz. The modulation results in a null interval of which the width measures the contrast threshold and of which the delay measures the apparent latency of the steady-state VEP, provided that the dynamic contrast sensitivity is symmetric. Data from 25 normal subjects and 27 patients with head injury show that this requirement is met in normal subjects but is often not verified in pathologic conditions. By measuring three aspects of the response to contrast changes (latency and static and dynamic contrast sensitivity) at five different spatial frequencies, one obtains a very sensitive method for investigation of the visual system.

Adolescent↗
PubMed1999

Effect of sleep state on the flash visual evoked potential. A case study.

Controversy exists regarding the influence of sleep state on the flash visual evoked potential. This study recorded the visual evoked potential in a new-born infant in four different sleep states; wakefulness. drowsiness, active sleep and quiet sleep over a five hour period. The infant's heart rate, breathing rate and breathing regularity were also recorded. It was clear that when this subject was awake the VEPs recorded differed substantially from those recorded when sleeping. Two of the four main components had shorter peak latencies, one component was prolonged and one of the peak to trough amplitudes was consistently smaller when alert. This study highlights an important and often overlooked aspect of developmental research that the state of the infant may affect developmental measures.

Evoked Potentials, Visual↗
PubMed1984

[Influence of low concentrations of halogenated anesthetics on the electroretinogram and visual evoked potentials in children].

During anaesthesia for neurophysiological investigations, halogen anaesthetics delivered at high concentrations altered visually evoked potentials. Low concentrations of volatile anaesthetics were proposed to avoid these alterations. Thirty young children, with visual or neurological abnormalities, were divided in two groups: the first group (n = 16), mean age of 20 months, was anaesthetized with halothane 0.5%, and the second (n = 14), mean age of 14 months, with enflurane 1.5%. Retinal action potentials (RAP) and visually evoked potentials (VEP) were obtained by computerized methods. The morphology of graphs before anaesthesia and after increasing concentrations of anaesthetics were compared. Height and latencies of the principal waves were measured. Low concentrations of halothane as well as enflurane avoided RAP and VEP disturbances. Nevertheless, no statistically significant data was obtained because of individual variations due to age, pathology and technical conditions.

Anesthetics↗