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Results for “Evoked Potentials, Visual”

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PubMed1989

An adaptive approach to spectral analysis of pattern-reversal visual evoked potentials.

A method for spectral analysis of pattern-reversal visual evoked potentials (PRVEP's) is presented that results in spectral peaks of uniform width in the frequency domain for signals with a wide range of time-domain duration. Uniformity of spectral peak width is necessary for accurate comparison of spectra. The desired frequency domain characteristics can be achieved through the application of "tunable" data windows prior to transformation. The Io-sinh (Kaiser), Gaussian, and cosine-taper (Tukey) windows were evaluated as to their ability to produce power spectra with uniform spectral peak width. Objective comparison of power spectra is based on the "spectral parameter," which is a numerical index of power distribution. Application of the method to PRVEP waveforms of normal subjects (N = 20) and to a population of Alzheimer's Disease patients (N = 15) showed the Io-sinh window to be the most effective method, yielding correct classification of all normal and abnormal subjects. The Gaussian window also performed well, with only two misclassifications. Use of the rectangular window resulted in seven misclassifications. The tapered-cosine window was very limited in its applicability, and was about equal in performance to the rectangular window.

Adult↗

PubMed1995

Latency measurement improvement of P100 complex in visual evoked potentials by FMH filters.

The ensemble average of Pattern Shift Visual Evoked Potentials (PSVEP) signals is seriously affected by random latency variations encountered in each individual sweep which is modeled as a continuous signal with linear segments and well-shaped triangular peaks. This effect is causing the smoothed peaks of the averaged PSVEP waveforms. It is our objective to restore the degraded peaks and provide accurate information about their exact location. The method used is based on nonlinear filtering of the FIR-Median Hybrid (FMH) type and is recommended as a postfiltering process to the well-known averaging methods of recovering PSVEP signals from noise by time-locking to stimuli. The new technique, tested in signals from clinical observations, has proven very promising.

Artifacts↗

PubMed1990

Do visual evoked potentials detect neural damage in children treated for cancer?

Abnormal visual evoked potentials (VEPs) have been reported in children treated for acute lymphoblastic leukaemia (ALL), which suggests that VEPs may be useful in screening for toxicity. The authors investigated this by recording flash and pattern VEPs in a control group of 34 siblings of patients, a group of six children studied longitudinally during the early stages of treatment for ALL, and three other follow-up groups. In only three follow-up patients were VEP results outside the normal range and the six ALL patients did not develop new abnormalities during early treatment. Although differences were detected between the groups, there was no evidence of VEPs being a useful means of monitoring the treatment of individual patients.

Adolescent↗

PubMed1993

Pattern-reversal visual evoked potentials in Down's syndrome.

We examined pattern-reversal visual evoked potentials (PRVEPs) in 36 adult patients with Down's syndrome, and analyzed the effects of the ophthalmological abnormalities on results of PRVEPs. The P100 latency was significantly delayed in 24 eyes of 16 patients. The P100 latency was significantly longer and its amplitude was significantly smaller (P < 0.001) in Down's syndrome patients than in age-matched normal controls. In 9 patients without any ophthalmological abnormalities, P100 latency showed no significant difference from that in normal controls, but three of them showed a significant delay of P100. Their P100 amplitudes were significantly smaller than those in normal controls. Therefore, we considered that the ophthalmological abnormalities are one of the main factors causing PRVEPs abnormalities in Down's syndrome patients, but some unknown factors should be also responsible.

Adult↗

PubMed1985

Alterations in transient visual-evoked potentials induced by clonazepam and sodium valproate.

The transient visual-evoked potentials (VEP), recorded in patients suffering from generalized epilepsy, can be characterized by a duplication of the negative peak with a latency of 70-100 ms, a strong increase in amplitude of the negative peak between 80 and 130 ms and the development of a high amplitude slow negative wave following the primary complex. In this study we have investigated to which degree these changes are influenced by the intravenous administration of clonazepam and sodium valproate. Therefore, VEPs were registered in 30 patients, suffering from generalized epilepsy, just before and immediately after the intravenous injection of 0.4-0.8 mg clonazepam and further at 15, 30 and 16 min thereafter. The same procedure was applied on 10 patients treated with an intravenous injection of 400 mg sodium valproate. In both groups we found more or less a reduction in number and degree of the mentioned VEP changes. The improvement was associated with a strong decrease in amplitude of the VEP components in the group treated with clonazepam but was not seen in the sodium valproate group.

Adolescent↗

PubMed1981

Birth asphyxia. I. Measurement of visual evoked potential (VEP) in the healthy fetus and newborn lamb.

The visual evoked potential (VEP) of five healthy, near-term exteriorized fetal lambs was compared with the VEP obtained from the same animals during the first hour after ventilation. Characteristics of the individual wave components and their relationship to blood pressure, heart rate, and arterial blood gas measurements concomitantly obtained were examined. Results show that the VEP of the healthy fetus is a stable, reproducible signal consisting of four basic components, and that the latencies (msec) and the amplitude (mu V) of the individual components of the VEP are similar to those of the newborn. In two related experiments, fetal asphyxia of unknown duration was encountered during fetal exteriorization an instrumentation. In the first case, neonatal, acidosis persisted despite aggressive resuscitation efforts and was accompanied by an atypical VEP. In the second case, the neonatal VEP obtained after 15 min of resuscitation was markedly depressed despite restoration of acid-base balance but gradually recovered during the remainder of the 1-hr newborn period. In conclusion, the VEP is a reproducible measure of cortical function in the healthy fetus and neonate and may reflect the acute status of cerebral function during fetal asphyxia and neonatal resuscitation.

Animals↗

PubMed1985

Visual evoked potentials by different check sizes in patients with multiple sclerosis.

Visual evoked potentials (VEPs) were obtained using three checks of different size (25', 50', and 100' of arc) in 20 normal controls and 1,006 patients. The test was abnormal in 270 patients regardless of the check size, whereas in 53 patients, a prolongation of P100 latency occurred only with checks of a certain size. The procedure was most sensitive in detecting abnormalities with combined application of 25' and 100' checks and least sensitive with the 50' checks alone. In occasional subjects showing W-shaped responses, the use of another check size often elicited the usual V-shaped pattern, alleviating the problem of selecting the peak for latency determination.

Adolescent↗

PubMed1993

Visual evoked potentials in multiple sclerosis: frequency response shows reduced alpha amplitude.

Visual evoked potentials were measured in a group of 16 multiple sclerosis (MS) patients and in a control group of 20 subjects. With respect to vertex and occipital recordings, latencies of main peaks were prolonged and response amplitudes were reduced in the MS group. As a result of frequency domain analysis we found that the amplitude reduction was not uniform in all frequency ranges: alpha (7-12 (Hz) components of EPs were markedly reduced whereas theta (4-7 Hz) responses were not altered. It is remarkable that the frequency components were altered to a different degree--this may shed some light on the physiological roles of the frequency components: As MS is frequently associated with optic neuritis, our interpretation of this frequency-dependent pattern is based on regarding MS as a model of impaired sensory input to the brain: the fact that in this situation alpha responses are markedly reduced hints at a link between alpha responses and primary sensory processing. Theta responses turned out to be unaltered--i.e., less dependent on sensory inputs--and might thus reflect associative sensory processing. This conclusion for functional roles of EP frequency components has also been drawn from previous investigations of topographic differences of EP frequency components.

Adult↗

PubMed2005

Effect of hypobaric hypoxia on visual evoked potential at high altitude.

The effect of hypobaric hypoxia on visual evoked potential (VEP) was studied in 27 male volunteers at sea level (SL), during the 1st and 3rd weeks of their stay at high altitude (HA) of 3,500 m and in the 1st week of their return to the sea level (RSL). Exposure to high altitude (HA) led to significant changes in VEP. The N1 wave latency of both right and left eye was significantly increased (P<0.05) during 3rd week of stay at the altitude which persisted even after the return to the sea level. The latency of P1 wave of both right and left eye was higher in 3rd week at high altitude but not significant statistically. But the delay in P1 latency persisted in 1st week of their return to sea level which was significant (p<0.05) statistically as compared to sea level. The latency of N2 wave was significantly decreased (P<0.05) during the 1st week of stay at HA and returned back to basal value in the 3rd week of stay at HA in both right and left eye. However, the changes observed in NPN complex in terms of wave latencies were within the physiological limits. The amplitude of wave N1-P1 of both the right and left eye did not show any change. The changes observed reflect the process of acclimatisation to 3500m high altitude.

Adult↗

PubMedDate not supplied

[Visual evoked potentials in chessboard pattern reversion in children with optic neuritis].

Visual evoked potentials (VEP) to chess pattern reversion were studied in 17 children with optic neurites during the acute stage and in the course of convalescence 1-2 months and 1-3 years after the disease onset. Coarse VEP changes were detected in the patients during the acute stage of optic neuritis. A positive time course of VEP was followed up in late periods after the acute attack of the disease. Despite normalization of vision acuity, no complete restoration of VEP to small-cell chess patterns was seen. The findings evidence that studies of VEP to chess pattern reversion should be carried out to detect subclinical involvement of the optic nerve and to timely diagnose optic neuritis in children.

Acute Disease↗

PubMed1991

[Neuro-monitoring using visual evoked potentials in comatose neurologic intensive care patients].

The application of visual evoked potentials (VEP) as a monitoring tool was studied in 40 comatose neurological intensive care patients. With increasing depth of coma, the number of detectable VEP components decreased. In deeply comatose patients, VEP were regularly displayed as a negative wave with a latency of app. 100 ms and an amplitude of app. 8 microV (N100). The administration of promethazine or flunitrazepam used as sedatives produced a decrease of amplitude and an increase of latency of N100 that was reversed within 30 or 60 min respectively. In 10 patients, in which intraventricular pressure (IVP) was measured continuously by means of an intraventricular catheter, it was found that increases of IVP produced a considerable decrease of the amplitude and area of N100; after reduction of the increased IVP, both parameters quickly recovered. These observations indicate that VEP may be a useful tool for neuro-monitoring in neurological intensive care patients.

Adult↗

PubMed1987

Pattern-reversal visual evoked potentials: latency changes with gender and age.

Pattern-reversal visual evoked potentials were studied in 123 volunteers with ages ranging from 20 to 77 years. The major positive component (P100) showed a shorter mean latency but a higher mean amplitude for females than males. The age-dependent increase in mean P100 latency was observed in the female group but not in the male group. The present data suggest that gender is more important than age in affecting the P100 latency.

Adult↗

PubMed1983

[Visual evoked potentials in pattern motion].

Our intention was to obtain a visual evoked potential (VEP) consisting only of a movement-related component for the purpose of further investigations of movement detection. This was attempted by selection of appropriate stimulus conditions. Evoked by initial movement a VEP with five typical waves was observed at the human occipital scalp. The N2-wave with a peak latency of 180-200 ms was most prominent. Following results were yielded in the experiments carried out: 1. Adaptation to a pattern movement: The amplitude of N2 and P1 is significantly reduced (Fig. 4). 2. Relation between amplitude and velocity: The experimental data could be approximated by a power function with an exponent of m = 0.3 for N2 and lower m for later waves (Fig. 5). 3. Pattern variation (grating, checkerboard, zig-zag) had no influence on N2 but on P1 and possibly also on later waves (Fig. 6). These results suggest that the wave N2 is movement-related under our experimental conditions. A pattern-related component may additionally be assumed in wave P2. Components, evoked by further reasons, may be included in the waves following N2. Their specification demands supplementary experiments.

Evoked Potentials, Visual↗

PubMed1993

[Visual evoked potentials and face recognition. Influence of celebrity and emotional expression].

Visual evoked potentials (VEP) were recorded in the right and left parietal and occipital regions of 40 right-handed controls in a facial recognition task. VEP were studied first according to the renown of the faces, then according to their emotional expression. Asymmetry was noted between the hemispheres: P100 was of greater amplitude and longer latency in the left occipital region. Later components (P400 and P600) were of greater amplitude and longer latency in the right parietal region in all situations. P100 latency on the left side was shorter for renowned faces than for non-renowned faces (P = 0.05). P600 latency was shorter on the right (P < 0.03) and left (P < 0.05) sides for smiling than for non-smiling faces. When the subjects were asked to look for emotional expression of the face (smiling or non-smiling) P400 was very ample and P600 of little amplitude. When the subjects were asked to recognize the face (renowned or not renowned) P600 was very ample and P400 of little amplitude. Thus, there seems to be a differential treatment of information: automatic and rapid to detect emotion (P400), controlled, tardy (P600) and involving memory in the search for renown.

Adult↗

PubMed1993

[Visual evoked potentials (VEPs) by leadings on scalp and dura in rabbits].

Visual evoked potentials (VEPs) were obtained from five rabbits. Responses to the photic stimulation were recorded by leading on scalp and dura. Stimulating conditions were changed in order of binocular, monocular (left and right) and screened binocular. The VEP waveforms leading on scalp and dura were composed of five positive and four negative peaks. The amplitude of the VEP leading on dura was about five times larger than that of the VEP leading on scalp. The VEP evoked by the monocular stimulation was characterized by the decreased amplitude in the ipsilateral hemisphere to the stimulated eye. It is furthermore characteristic in the dural recording that the major negative peaks in the early component disappeared in the same side as the stimulated eye. These differences in the VEP evoked by the monocular stimulation might reflect that the most projection of optic nerve cross at the optic chiasm in rabbits.

Animals↗

PubMed1996

Sex differences in visual evoked potential and electroencephalogram of healthy adults.

Sex differences in flash visual evoked potentials (VEPs) and electroencephalograms (EEGs) were studied in 200 healthy adults (100 females and 100 males). Following results were obtained. (1) Waveforms of Group Mean VEPs of each sex had roughly triphasic contour, consisted of components P1 approximately N8, within 500 msec of latency. (2) Latencies of VEP components by t-test, (3) By analysis of covariance, sex differences in peak-to-peak amplitudes were still significant after eliminating effects of body height, body weight or age, but not those in latencies after eliminating the effect of body height. (4) Quantitative analysis of EEGs resulted in significantly smaller absolute amplitudes, and significantly larger theta, larger beta 1 and smaller alpha 2 power % in females. (5) Peak-to-peak amplitudes of later components in VEPs for 5CH (O1-->Cz) were significantly and positively correlated with EEG absolute amplitudes within each sex group. (6) There were few significant differences in VEP components between follicular phase and luteal phase in females. The sex differences in VEPs verified in this study may be attributed to genetically determined sex differences in neuroendocrinological systems.

Adult↗

PubMed1976

[Diagnosis of hydrocephalus. Changes in visual evoked potentials in children with progressive hydrocephalus internus].

Visual evoked potentials (VEP) of 12 children with progressive hydrocephalus internus were studied. Depending on the severity of hydrocephalus internus VEP show remarkable changes. First of deformation of VEP occurs, than a slowing of latencies and finally an extreme increase of latencies combined with a further deformation of VEP. The whole duration of the VEP shows a marked prolongation.

Evoked Potentials↗

PubMed1978

Delayed visual evoked potentials with bilateral disease of the posterior visual pathway.

A man of 51 years presented with sudden onset of a confusional state and marked visual deterioration. The computerised transaxial tomogram showed a mass in the corpus callosum which had spread to involve both cerebral hemispheres. The visual evoked potential to pattern stimulus was delayed by about 20 ms. Necropsy confirmed the presence of an astrocytoma of the corpus callosum involving the optic radiation and occipital cortex on both sides. The anterior visual pathway was normal.

Astrocytoma↗