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Results for “Evoked Potentials, Visual”

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PubMed1980

The effect of adaptation to the stimulating pattern on the latency and wave form of visual evoked potentials.

Visual evoked potentials (VEPs) elicited with a checkerboard stimulus after adaptation to an unpatterned grey field were compared to those obtained after adaptation to the stimulating pattern for an equal interval of time. When 3--4 sec elapsed between the adapting interval and recording of the VEP, the latency of the principal positive peak increased by 4 msec with pattern-reversal, but not with pattern-onset stimulation, while the amplitude was unchanged. However, when the pattern-onset VEP was recorded immediately after adaptation, the principal negative peak of the response was lost and the latency of its principal positive peak increased by 14 msec, causing it to mimic the conventional pattern-reversal VEP in both wave form and latency, and suggesting that adaptation may cause the wave form differences in the VEPs obtained by these two methods.

Adult↗

PubMedDate not supplied

Hierarchical decomposition of dichoptic multifocal visual evoked potentials.

Visual evoked responses to dichoptically presented multifocal stimuli were recorded for 92 eyes. Two stimulus variants were explored: temporally sparse and rapidly contrast reversing. We used hierarchical decomposition (HD) to represent the multifocal responses in terms of a small number of potentially unique component waveforms that are interrelated in a multivariate linear autoregressive (MLAR) relationship. The HD method exploits temporal correlations over a range of delays in the responses to estimate parallel, feedforward and feedback relationships between the HD components. Three HD components having temporal interrelationships constrained (at P < 0.05) to a moving approximately 20 ms window could describe the multifocal responses well (median r2-values up to 90%). HD components were similar for both stimulus types and the component waveforms were temporally correlated, especially the first and third components. The data set was large enough to estimate separate HD components for each multifocal stimulus region. The component waveforms differed somewhat by region but the MLAR relationships were similar. At short delays parallel processing dominated. At longer delays the proportion of response drives that were attributed to feedback and feedforward relationships grew. Overall HD analysis seems to provide an informed summary of multifocal responses and insights into their sources.

Adult↗

PubMedDate not supplied

Age-related changes in the relationship between visual evoked potentials and visually evoked cerebral blood flow velocity response.

We evaluated neurovascular coupling during normal aging using visual evoked potentials (VEPs) and visually evoked cerebral blood flow velocity responses (VEFRs). The recordings were made from a group of healthy younger and older subjects. The stimulus was a black and white checkerboard with visual contrasts of 1%, 10% and 100%. The VEFRs were measured in the posterior cerebral artery using transcranial Doppler simultaneously with VEPs from occipital leads. A significant increase in the VEFRs and VEPs in response to graded visual contrasts (p<0.01) was found in both groups. Linear regression analysis showed a significant positive association between the VEPs and the VEFRs in the younger (r=0.66, p<0.01) and older subjects (r=0.74, p<0.01). We also found significant differences in neurovascular coupling index (VEFR/VEP) between both groups at each visual contrast (p<0.01). We conclude that simultaneous recording of VEFRs and VEPs at graded visual contrasts indicated attenuated neurovascular coupling in older subjects.

Adult↗

PubMed1989

[Visually evoked potentials and visual acuity of the young child].

Interest in the development of visual acuity in young infants is increasing. At this age a reliable estimation of visual function is hazardous. This paper highlights the role of flash- and pattern evoked visual potentials. Flash evoked potentials are valuable in following development and/or recovery of visual acuity intra-individually as well as in providing an estimation of sensitiveness to light. Pattern evoked potentials may give an estimation of maturation of the visual system: these potentials also give an objective measurement of visual acuity.

Child, Preschool↗

PubMed1999

Normalization of auditory evoked potential and visual evoked potential in patients with idiot savant.

OBJECTIVE: To investigate the variations of auditory evoked potentials (AEP) and visual evoked potentials (VEP) of patients with idiot savant (IS) syndrome. METHODS: Both AEP and VEP were recorded from 7 patients with IS syndrome, 21 mentally retarded (MR) children without the syndrome and 21 normally age-matched controls, using a Dantec concerto SEEG-16 BEAM instrument. RESULTS: Both AEP and VEP of MR group showed significantly longer latencies (P1 and P2 latencies of AEP, P < 0.01; N1 and N2 latencies of VEP, P < 0.01/0.05), lower P2 amplitudes (P < 0.01) and higher P3 amplitudes (P < 0.01), as compared with normal controls. But none of above-mentioned changes was found with IS group. Almost all MR patients (90.1%) presented P4 component in both AEP and VEP, which was also in sharp contrast with its incidence in other 2 groups (IS: 14.3%; normal controls: 9.5%). CONCLUSION: Patients with idiot savant syndrome presented normalized AEP and VEP.

Adolescent↗

PubMed2000

[Pattern visual evoked potentials visual acuity--the evaluation of visual acuity of less than 0.1].

PURPOSE: We previously developed a new method for estimating objective visual acuity by means of pattern visual evoked potentials (PVEP). In this study, this method was applied to the evaluation of visual acuity of 0.05 and 0.01. METHODS: Ten subjects with visual acuity of 0.05 and ten normal subjects with visual acuity of 0.01 were examined. The visual acuity of the subjects was decreased step by step by means of plus spherical lenses of increasing power. In the PVEP study, the stimulus consisted of black and white checkerboards with a visual angle of 8 degrees (central stimulus) and a global field with a 5 degrees central circular scotoma (peripheral stimulus), contrast level of 15%, and a frequency of 0.7 Hz. One hundred PVEP responses were averaged per session. We reported that there was a linear relation between log subjective visual acuity of 0.1-1.0 and log check size of the patterns with PVEP. In reference to that, the check sizes of the patterns were estimated at 66' with visual acuity of 0.05, and 107' with visual acuity of 0.01. Each visual acuity was then used with other check sizes of three patterns. RESULTS: With central stimulus the P100 components of O1, O2, and Oz were recorded with 66' and 82' patterns at visual acuity of 0.05(central stimulus). The P100 components of O1, O2, and Oz were 107', 137' and 161' at visual acuity of 0.01(central stimulus). There was no P100 component at visual acuity of 0.05 and 0.01(peripheral stimulus). CONCLUSION: This method of PVEP is a useful tool as an objective estimation of visual acuity less than 0.1 and is presumed to stimulate preferentially the X retinal ganglion cell to parvocellular pathway.

Adult↗

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↗

PubMed1999

Effects of low alcohol consumption on visual evoked potential, visual field and visual contrast sensitivity.

PURPOSE: We studied changes in the vision of 16 people after consumption of a small quantity of alcohol, at a blood alcohol level (BAL) of 0.57 g/kg. METHODS: We studied visual contrast sensitivity (VCS) using Vistech VCTS 6500, visual evoked potential (VEP) by checked pattern stimulations and the peripheral visual field (PVF) with a perimetric automatic Humphrey. We first carried out the tests on sober people and then on individuals with a BAL of 0.57 g/kg. RESULTS: Alcohol consumption caused no significant difference in performance for these 3 tests. However, at a BAL of 0.57 g/kg there was a decrease in cerebral function, as shown by an increase in the number of mistakes made in the Wisconsin Card Sorting Test. CONCLUSION: These results suggest that for a low blood alcohol level, visual performance is less affected by the visual changes than by alteration in brain functions.

Adult↗

PubMedDate not supplied

[Electrophysiologic follow-up (brainstem acoustic evoked potentials and visual evoked potentials) in chronic uremic patients treated with various therapeutic protocols].

The aim of our study was to evaluate the possibility of recording also sub-clinical alterations of the Central Nervous System during chronic uremia by means of the study of Pattern-Reversal Visual Evoked Potentials (P-R V.E.Ps) and Brainstem Acoustic Evoked Potentials (B.A.E.Ps), to study their behaviour in answer to different kinds of treatment and follow their possible modifications during the time. With this purpose the uremic patients were divided into therapeutic groups: only dietetic and pharmacological treatment, conventional hemodialysis, hemodiafiltration, peritoneal dialysis and well functioning kidney transplant. A first record of Evoked Potentials was made in 1985 and the values were compared with those obtained by an homogeneous control group. The same patients were evaluated 3 years later and the two records results were compared. In both cases the most important percentage of altered values were found in the group under only dietetic and pharmacological treatment, the less important in the transplanted patients and these data were stable at the follow-up. So that Evoked Potentials are a good test in chronic uremia and the best therapy able to hinder the alterations of Central Nervous System arising during chronic renal failure would seen to be kidney transplant.

Adult↗

PubMed1996

Brainstem auditory evoked potentials and visually evoked potentials in young patients with IDDM.

OBJECTIVE: To investigate whether young IDDM patients develop central nervous dysfunction and to establish a possible relationship with various disease parameters. RESEARCH DESIGN AND METHODS: Thirty-two patients, aged 13.5 +/- 2 years, with disease duration of 6 +/- 2.6 years and age of onset of 7.7 +/- 3.2 years (group 1), and 21 patients with short-term disease, age 9.7 +/- 3.5 years, duration of disease < 2 years and age of onset of 9.4 +/- 3.3 years (group 2) were compared with age- and sex-matched control subjects. Exclusion criteria were clinical signs of neuropathy, retinopathy, nephropathy, or hearing impairment. Neurophysiological studies included auditory and visually evoked potentials (EPs). RESULTS: Patients in group 1 revealed increased P100 latencies of visually EPs (103.4 +/- 4.5 vs. 96.8 +/- 3.7 ms) and interpeak latencies I-V of auditory EPs (4.16 +/- 0.10 vs. 3.99 +/- 0.09 ms) and had abnormal latencies (values outside 2.5 SD) in 37%. However, short-term patients (group 2) had results within normal limits compared with control subjects. In group 1, longer disease duration and younger age at onset correlated with an increase of P100 latency (P < 0.001) and IPL I-V (P < 0.001). Patients with a history of severe hypoglycemic episodes had increased latencies compared with patients without hypoglycemia (P < 0.05). Furthermore, metabolic control during the last 2 years was related to P100 latencies (P < 0.05). CONCLUSIONS: EPs noninvasively detect subclinical central nervous system involvement in children and adolescents with IDDM. Most important risk factors are duration of disease and frequency of severe hypoglycemia.

Acoustic Stimulation↗

PubMed1997

Brain stem evoked potentials and visual evoked potentials in relation to the length of occupational exposure to low levels of toluene.

In 49 printing-press workers occupationally exposed to toluene for approximately 21.6 years, the values of BEAP and VEP parameters were examined in relation to the length of exposure. With the exception of P2 wave, there was a significant increase in the latencies of all the BEAP waves examined as well as in the interpeak latency (IPL) P3-P4, whereas IPL P4-P5 decreased significantly with the length of exposure. The amplitude of all the VEP examined decreased significantly with the length of exposure. Toluene exposure was evaluated by measuring the concentration of toluene in peripheral blood and of hippuric acid in urine on Wednesday morning prior to the workshift, and of hippuric acid in urine after the workshift on the same day. According to the average concentration of hippuric acid in urine after the workshift, the levels of toluene exposure were estimated to range from 40-60 ppm. Evoked potentials were determined on Mondays 10-12 hours after a nonworking weekend.

Adult↗

PubMed1999

Menstrual cycle synchronized changes in brain stem auditory evoked potentials and visual evoked potentials.

BACKGROUND: Several studies have reported changes in the spontaneous electroencephalogram of women across the menstrual cycle (MC), raising questions on whether sensory or cognitive evoked potentials would change with MC as well. Some of these studies have found changes synchronized with MC in visual event-related brain potentials (ERPs) and brain stem auditory evoked potentials (BAEPs), whereas others have reported none. METHODS: In the present study, we attempted to study the changes in P300 component of visual ERPs, and in BAEPs across the MC in healthy women. RESULTS: The latency of P300 was longer during the ovulatory phase. Decrease across the MC phases was found for the amplitude of BAEP waves I and III, and for the wave V latency and the III-V interpeak latency. CONCLUSIONS: The results indicate that there may be a small relationship between visual ERP or BAEP and MC phase.

Adult↗

PubMedDate not supplied

[Effect of diazepam on visual potentials evoked by reversible checkerboard pattern].

Visual potentials evoked by means of reversible checkerboard pattern were studied in 12 healthy subjects, 5 patients with probable multiple sclerosis and 3 patients with photosensitive epilepsy before and after intravenous injection of 10 mg of Valium. The most characteristic feature was lowering of the amplitude of the evoked visual potentials (in 75%) which appeared as a rule between 30 seconds and 4 minutes after Valium injection. Prolongation of Pmax latency was observed less frequently (in 65%) and this change was of low grade. In nearly half the cases sings of synchronization appeared with development of late multiphasic components of the visual evoked potential. No significant difference was noted in the effect of Valium on the latency and amplitude of the visual evoked potentials between healthy subjects and patients. The possible mechanisms of diazepam action on the conduction in visual pathways are discussed.

Diazepam↗

PubMed1991

Visual evoked potentials and visual prognosis following perinatal asphyxia.

Twenty-five children born at term with perinatal asphyxia were studied at age 2.5 to 4.5 years to evaluate visual function and to determine the prognostic value of postnatal assessments of visual outcome. Postnatal assessments included several visual evoked potentials and electroretinograms in the first week of life. Follow-up assessments included flash and pattern visual evoked potentials, visual evoked potential threshold measurements, and clinical eye examinations. Nineteen children had normal visual function, three were visually impaired, and three remained blind. A strong association was found between normal, abnormal, or absent visual evoked potentials in the early postnatal period and long-term visual outcome (P less than .0001). Other perinatal indicators of asphyxia, including neurologic status, Apgar scores, and arterial pH values, were poor predictors of visual outcome. The risk of visual impairment was limited to those survivors with neurodevelopmental deficits.

Asphyxia Neonatorum↗

PubMedDate not supplied

[The interrelation of the level of the brain DC potential and visual evoked potentials during human aging: the norm and Alzheimer's disease].

Correlation between DC-potential level and visual evoked potentials (VEP) was investigated in normal subjects of the middle and old age and the patients with Alzheimer's disease. Significant correlation between the DC-potential level and the amplitudes and latencies of different components of VEP was found. The correlation was intensified during ageing mostly in patients. More stable positive correlation existed between local DC-potential level recorded in the occipital area of the head and the amplitude of the components N1 and P2 of VEP.

Adult↗

PubMedDate not supplied

[Cortical and spinal evoked potentials in parkinsonism. Part I. Visual potentials evoked with a checkerboard pattern].

In 21 patients with parkinsonism and 20 healthy controls visual potentials evoked with checker pattern used as an alternating stimulus were studied. The left and right eye were examined separately recording visual cortical responses in the central occipital area. The analysed elements included the latency of the first highest positive wave P100 and the amplitude of the P100/N120 complex. Prolongation of the mean latency of P100 was found in patients with parkinsonism, but it was not significant statistically. No differences were found of the P100/N120 amplitude in the group with parkinsonism in relation to healthy controls. In the patients with parkinsonian syndrome (mainly of atherosclerotic origin) the mean latency of the visual potentials was longer and the amplitude was lower than in cases of Parkinson's disease. Attention is called to the high variability of the visual evoked potentials related to the clinical state and origin of the disease (parkinsonian syndrome and Parkinson's disease).

Aged↗

PubMed2006

Brainstem auditory evoked potentials and flash visual evoked potentials in Vietnamese miniature pot-bellied pigs.

Brainstem auditory evoked potentials (BAEP) and flash visual evoked potentials (VEP) were recorded from juvenile (5-7 weeks of age) and adult Vietnamese miniature pot-bellied pigs to provide normative data for clinical applications. BAEP responses were collected in response to stimulus intensities of 85, 95, and 105 dB nHL. VEP responses were collected in response to flashes of white light in a darkened room. Left-right ear and left-right eye responses did not differ significantly, and were combined for analysis, with each animal providing two data points for each response. BAEP responses in juvenile subjects were mature, and in all subjects showed the typical pattern of decreasing peak latencies and increasing peak amplitudes with increasing stimulus intensity. VEP responses in juvenile subjects were near to mature values, but the latencies still exceeded those of adults. Differences in response maturation between precocial and altricial species are discussed.

Aging↗

PubMed1987

Visual resolution and sensitivity in a nocturnal primate (galago) measured with visual evoked potentials.

Visual resolution and contrast sensitivity were examined in anesthetized, paralyzed galagos using visual evoked potentials (VEPs) resulting from stimulation with phase-reversed sinewave gratings. Spatial frequency vs contrast response functions were band-pass with peak sensitivity at 0.2-0.4 c/deg and a high frequency cut-off between 1.6 and 3 c/deg. Peak contrast sensitivities (estimated from extrapolation of contrast response functions) varied across animals from 10 to 170. Variation of the stimulus modulation rate showed that best responses occurred at 1 Hz with an upper limit of 6-16 Hz. As in other primates, an oblique effect was seen in 6 of 8 animals. The contrast sensitivity function (CSF) determined from cortical VEPs agrees well with the CSFs of cells in the lateral geniculate nucleus, but peak sensitivity and spatial frequency are slightly lower than found for the behavioral CSF. Overall visual performance resembled closely that of another nocturnal species, the cat.

Animals↗