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PubMed2004

Automatic Discrimination of Abnormal Subjects Using the Visual Evoked Potential Spectral Components.

Study of visual evoked potential (VEP) is one of the utilized methods in clinical diagnosis of ophthalmology and neurological disorders. The automatic detection of VEP spectral components is an important tool in the diagnosis of mental activity. This paper presents a novel computational approach using feedforward neural network to identify abnormal subjects from changes in spectral components. The output vector from the feedforward neural network is based on the VEP spectral components. The software was developed to identify mental state from the VEP spectral components using Matlab software package. Using this approach, it is possible to perform real-time abnormality identification accurately on personal computers.

Journal Article↗
PubMed1988

The influence of grating contrast on the human cortical potential visually evoked by motion.

A cortical potential was evoked by the onset of horizontal drift of a previously stationary vertical square-wave grating (motion-on VEP). The influence of contrast on the principal VEP waves N2 and P2 (peak latencies 180-220 ms and 250-350 ms, respectively) was investigated in five subjects for velocities between 0.3 and 4.1 deg/s, a spatial frequency of 2.6 c/deg and a mean luminance of 17 cd/m2. For low contrasts an ascending linear relation could be found between wave amplitude and logarithm of contrast, and a descending one between wave peak latency and log contrast. The waves remained constant for moderate and high contrasts. The lowest contrast value at which wave constancy occurred (saturation contrast) was determined by a method of least squares. All the data summarized yielded a saturation contrast of 0.058 for N2 and 0.084 for P2. The saturation contrast of the pattern VEP already known from the literature is essentially greater under comparable experimental conditions.

Adult↗
PubMed1983

[Auditory evoked brain stem potentials, visual pattern evoked and somatosensory evoked potentials in transient ischemic attacks (TIA)].

Auditory-evoked brainstem potentials, visual pattern-evoked and somatosensory-evoked potentials in transitory ischemic attacks (TIA). Pathological findings in patients suffering from transitory ischemic attacks by means of using neuroradiological methods (CCT included) are a rare condition. The combination of visual checkerboard-evoked potentials (VEP), auditory brainstem-evoked (AEP) and somatosensory-evoked potentials (SSEP) can detect functional lesions in cerebral regions with different blood supply but without diagnostic risk. A delay of peak III of the AEP is possibly of specific value with regard to brainstem lesion caused by TIA in our patients.

Audiometry↗
PubMed2004

Methods of visual acuity determination with the spatial frequency sweep visual evoked potential.

PURPOSE: The spatial frequency sweep visual evoked potential (sVEP) is used to rapidly determine visual acuity in children or non-responsive patients. Two techniques have been used to separate signal from noise: (1) the 95% confidence interval for the signal amplitude (95% CI) or (2) the amplitude of a Fourier frequency adjacent to 2x the signal frequency (DFT). The purpose of this study is to determine if there is a significant difference in acuity estimates with these techniques. METHODS: Ten normal subjects (approximately 0.00 logMAR acuity) and 11 patients with decreased visual acuity took part in this project. Stimulus production and data analysis were done with an Enfant 4010 (Neuroscientific Corp). Standard VEP recording techniques were employed. The stimulus was a horizontal-oriented, sine wave grating that swept up the spatial frequency spectrum (contrast 80%, temporal reversal rate 7.5 Hz). Sweeps were repeated until the confidence intervals for the data were no longer decreasing. The Bailey Lovie logMAR chart was used to determine visual acuity. A line was fit to the high spatial frequency data using either the 95% CI or the DFT as the noise estimate. By using these linear equations, acuity estimates were obtained at 0, 1, and 2 microV signal amplitudes. RESULTS: The average logMAR acuity for the subjects with normal acuity was -0.06 +/- 0.070 (SD). The sVEP acuity estimates were 0.08 +/- 0.098, 0.18 +/- 0.092, and 0.33 +/- 0.195 (0, 1, and 2 microV extrapolations) with the 95% CI used as noise and 0.07 +/- 0.100, 0.18 +/- 0.103, and 0.33 +/- 0.202 (0, 1, and 2 microV extrapolations) with the DFT used as noise. By using the average noise from the Fourier frequency as the extrapolation level, the acuity was 0.10 +/- 0.098 logMAR. The average logMAR acuity for the subjects with decreased visual acuity was 0.67 +/- 0.306 (SD). The sVEP acuity estimates were 0.53 +/- 0.175, 0.66 +/- 0.171, and 0.88 +/- 0.295 (0, 1, and 2 microV extrapolations) with the 95% CI used as noise and 0.53 +/- 0.179, 0.65 +/- 0.176, and 0.86 +/- 0.268 (0, 1, and 2 microV extrapolations) with the DFT used as noise. By using the average noise from the Fourier frequency as the extrapolation level, the acuity was 0.57 +/- 0.186 logMAR. No significant difference was found between the two acuity estimate techniques for all of the subjects (repeated measures ANOVA, p = 0.16, F20 = 2.131). The sVEP estimates of acuity to the 0 microV and noise levels were not significantly different from the logMAR acuity (paired t-test, all p values > 0.05). CONCLUSIONS: The results indicate that the sVEP acuity does not depend on the noise estimation technique. In agreement with prior studies, the sVEP acuity underestimates the logMAR acuity in normally sighted individuals by about an octave.

Adolescent↗
PubMed2001

Effects of ethanol on human visual evoked potentials.

Studies of the effect of ethanol on human visual evoked potentials are rare and usually involve chronic alcoholic patients. The effect of acute ethanol ingestion has seldom been investigated. We have studied the effect of acute alcoholic poisoning on pattern-reversal visual evoked potentials (PR-VEP) and flash light visual evoked potentials (F-VEP) in 20 normal volunteers. We observed different effects with ethanol: statistically significant prolonged latencies of F-VEP after ingestion, and no significant differences in the latencies of the PR-VEP components. We hypothesize a selective ethanol effect on the afferent transmission of rods, mainly dependent on GABA and glutamatergic neurotransmission, influencing F-VEP latencies, and no effect on cone afferent transmission, as alcohol doesn't influence PR-VEP latencies.

Adult↗
PubMed1994

Binocular enhancement of the visual evoked potential in patients with Duane's syndrome.

Monocular and binocular visual evoked potentials were recorded in eight patients with Duane's syndrome who used an abnormal head posture to maintain binocular single vision. With their abnormal head posture, all patients had stereoscopic vision, although with mildly reduced stereoacuity, and the visual evoked potential showed binocular enhancement (mean binocular to monocular ratio, 1.44). Without their head posture, the patients experienced diplopia or suppressed vision in one eye. Binocular visual evoked potentials recorded under these conditions were of lower amplitude (mean binocular to monocular ratio, 1.05). However, without the abnormal head posture, a manifest strabismus was present and the deviating eye was not fixating the stimulus screen. Monocular visual evoked potentials recorded with the eye fixating just to one side of the screen gave little or no response, and this lack of fixation may account for the loss of binocular enhancement of the visual evoked potential in strabismus.

Adult↗
PubMed1983

Altered visual-evoked potentials in congenitally deaf adults.

Visual-evoked potentials recorded from the scalp of congenitally deaf adults were significantly larger over both auditory and visual cortical areas than in normal hearing adults. Over temporal and frontal areas peripheral stimuli presented at long intervals elicited N150 components which were larger in deaf than in hearing subjects. Over occipital and parietal areas peripheral and foveal stimuli elicited larger P230 components in deaf than in hearing subjects. These results imply that early auditory experience influences the organization of the human brain for visual processing.

Adult↗
PubMed1979

Deficits in the visual evoked potentials of cats as a result of visual deprivation.

Visual evoked potentials in response to contrast reversal of grating patterns were used as a measure of visual function in normal and visually deprived cats. In cats which had been dark reared from birth (BD cats) there was a characteristic change in VEP waveform from normal, for both eyes and for all spatial frequencies of testing stimulus. In cats which had one eye sutured from the age of one week (MD cats), the VEP from the deprived eye was smaller for contrast reversal of coarse patterns. Kittens given only restricted periods of monocular exposure gave VEPs which resembled the pathological responses of the BD cats. However, the amplitudes of response were larger for the more experienced eye at higher spatial frequency. This work reinforces the idea that two factors govern cortical development: competition and experience. Lack of sufficient visual experience leads to severe intracortical pathology.

Aging↗
PubMedDate not supplied

[Visual evoked potential in leprosy patients].

PURPOSE: To verify the possible alterations in visual evoked potential of leprosy patients. METHODS: Visual evoked potential examinations were performed in 13 Hansen disease patients, 5 of them with the multibacillary form and 8 with the paucibacillary. This was done at the moment of the diagnosis. The control group enrolled 15 health individuals, without Hansen disease. RESULTS: The measurement result varied from 102.0 to 120.5 ms, with a mean of 110.1+/-5.7 ms. In the multibacillary form, the values varied from 109.0 to 120.0 ms, mean 111.1+/-5.4. In the paucibacillary, the values varied from 102.0 to 120.5 ms, with a mean of 109.5+/-6.1 ms. The latency values were significantly greater in Hansen disease patients (p<0.0001), even if multibacillary and paucibacillary forms were compared separately. However, there was no significant difference when the pauci- and multibacillary groups were compared. CONCLUSION: The latency values were significantly greater in leprosy patients. A recommendation can be made for these patients, which is to be submitted to early visual evoked potential as a rule in order to investigate ocular complications, as well as to prevent damages.

Adolescent↗
PubMed1994

Covariability of visually evoked potentials and simple motor reaction times.

Visually evoked potentials (VEPs) were recorded during simple motor reaction time (RT) experiments using spatially localized, contrast modulated visual stimuli. VEPs were averaged in groups, called "subensembles," depending on the speed of the subject's motor response. To a specific visual stimulus, the VEP response time of a subensemble covaries with motor response latency according to the same linear relationship found to describe conventionally averaged VEPs and RTs over a wide range of stimuli.

Electroencephalography↗
PubMed1995

Multichannel visual evoked potentials in migraine.

Multichannel recordings of visual evoked potentials (VEPs) have proved to be useful in the evaluation of visual field defects. We studied the topographic distribution of transient VEPs in 15 migraine patients (8 with visual aura and 7 without) and 15 age-matched controls during the migraine-free interval. All the subjects included in the study had normal visual fields. VEPs were recorded from 9 electrodes placed on the posterior scalp. Stimuli were full-field and hemifield reversing square wave grating patterns of medium spatial frequency (4 c/deg). The groups did not show significant differences in latencies and amplitudes of the major components (N70, P100) recorded from the midline. However, migraine patients with visual hemianopic aura showed definite asymmetries in the VEP amplitude distribution. Significantly reduced, absent or polarity-invered VEP responses were recorded ipsilateral to the side of the prodromic visual symptoms. Direct comparison of affected and unaffected hemispheres by partial field stimulation confirmed these findings. According to the VEP cortical generator theory, these abnormalities suggest a functional anomaly consistent with the clinical syndrome and detectable also in the migraine-free interval. None of the migraine patients without aura or the controls showed VEP amplitude asymmetries. We conclude that multichannel VEP recordings may discriminate between different subtypes of migraine and contribute important physiopathological information to the study of this disease.

Adolescent↗
PubMed1989

Predictive value of visual evoked potentials in unilateral optic nerve injury.

Forty-five patients with posttraumatic unilateral blindness were prospectively analyzed. The computed tomography scan was normal in all and an optic canal fracture was recorded in only one patient. Visual evoked potentials were performed within 48 hours of initial evaluation and repeated within 7 to 10 days. Five patients had normal visual evoked potentials and 15 patients had abnormal responses. No visual evoked potentials were recorded in 25 patients. Five patients with normal visual evoked potentials had good visual recovery. Thirteen of the 15 patients with abnormal responses also showed significant visual improvement. This study showed that positive visual evoked potentials were reliable in predicting the visual outcome; 90% of the patients with positive visual evoked potentials had complete or partial visual recovery.

Adult↗
PubMed1997

Pattern-reversal visual evoked potentials in patients with epiretinal membrane.

PURPOSE: To determine the extent of pattern-reversal visual evoked potential parameter alteration by epiretinal membranes and to investigate the use of pattern-reversal visual evoked potential in the estimation of macular function in eyes with epiretinal membrane and in the fellow eyes. METHODS: In both eyes of 162 patients with epiretinal membrane, 92 of primary and 70 of secondary origin, pattern-reversal visual evoked potentials were recorded. Check sizes of 17', 10', and 7' (minutes of arc) were used. Parameters investigated were N80 and P100 latencies and P100 amplitude. RESULTS: No significant difference was detected between eyes with epiretinal membrane of primary and secondary origin regarding visual acuity and the pattern-reversal visual evoked potential parameters for the different check sizes. Compared with the fellow eyes, the eyes with epiretinal membrane had a significantly reduced visual acuity, prolonged N80 and P100 latencies, and a reduced P100 amplitude for the different check sizes. Compared with a separate control group (N = 20) with patients 50 to 59 years old, eyes with epiretinal membrane (N = 9) showed the same features as in the total group, but only for the 17' and 10' check sizes. The fellow eyes (N = 9) showed a significant reduction of the P100 amplitude (P < .05) for the pattern sizes of 17' and 10', but no difference in visual acuity or pattern-reversal visual evoked potential latency was found. CONCLUSIONS: In eyes with epiretinal membrane, pattern-reversal visual evoked potential latencies are prolonged, and amplitude is reduced. Relationships between clinical parameters and pattern-reversal visual evoked potential parameters require further study.

Evoked Potentials, Visual↗
PubMed1995

Discriminative power of visual evoked potential characteristics in multiple sclerosis.

To investigate the discriminative power of pattern-reversal visual evoked potential characteristics (peak latencies and amplitude) and to test whether the addition of visual evoked potential amplitude can increase the power of the visual evoked potential in the diagnosis of multiple sclerosis, we retrospectively studied visual evoked potentials in 59 patients with definite multiple sclerosis and 126 control subjects. Two check sizes (17' and 10') were used. Females had significantly higher amplitudes and shorter latencies than males. N80 latency showed a gradual increase and P100 amplitude a decrease with age. P100 latency was stable between the ages of 20 and 55 years but was increased in childhood and the elderly. The significance of visual evoked potential peak latencies and amplitude in separating the two groups was investigated by means of a (multivariate) discriminant analysis. The visual evoked potential with a pattern of 10' could be measured in 58% of patients with multiple sclerosis. The exclusive use of the P100 amplitude in the discriminant analysis resulted in a percentage of correctly classified cases of 84%, whereas for P100 and N80 latency it was 85% and 90%, respectively. With the 17' pattern, the N80 latency yielded also a higher correct percentage than did the P100 latency. Although N80 latency is, to a greater extent than P100 latency, influenced by age, sex and size of stimulus pattern, when these influences are accounted for, the N80 latency is a more sensitive measure than P100 latency in the classification of multiple sclerosis. Combined use of latency and amplitude for discriminant analysis yielded no significant improvement of the percentage of correctly classified cases.

Adolescent↗
PubMed1998

Muscle-eye-brain disease: clinical features, visual evoked potentials and brain imaging in 20 patients.

Clinical features, magnetic resonance imaging and visual evoked potentials were analysed and correlated in 20 Finnish patients with muscle-eye-brain disease. Significantly enhanced visual evoked potentials were found in 15 patients (giant in 14 of them). Magnetic resonance images were available in 17 cases. The images of 12 patients with giant visual evoked potentials showed typical brain malformation pachygyria with a nodular cortical surface i.e. cobblestone cortex, midline defect and hypoplastic pons but no significant abnormalities in the grey-white matter. One male had typical structural changes but flat visual evoked potentials. His extreme hydrocephalus with optic nerve compression may explain the findings. No structural changes on magnetic resonance images were found in the remaining four patients; however, in two of them marked alterations in the white matter were found. Three of these patients showed normal and one flat visual evoked potentials. Only one patient with giant visual evoked potentials and typical structural findings on magnetic resonance imaging had changes in a large area in the white matter (several attacks of status epilepticus might have caused the alterations in the white matter). Thus, the combination of giant visual evoked potentials and typical structural changes on magnetic resonance imaging with normal intensities of white matter and deep grey matter seems to be a good marker for patients with muscle-eye-brain disease.

Abnormalities, Multiple↗