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Results for “Evoked Potentials, Visual”

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PubMed2003

Visual evoked potentials to line- and luminance-defined triangles.

Processing of line- and luminance-defined triangles was investigated by studying visual potentials (VEPs) evoked by triangles. Twenty-six subjects were randomly presented with line, grey, and illusory triangles. Relative to VEPs elicited by grey and illusory triangles, VEPs to line triangles included P220s that were smaller at frontal sites but larger at occipital sites, and N260s that were smaller over both temporal and occipital sites. It is proposed that, in contrast to triangle defined by a line, illusory and luminance-defined triangles include information involved in the processing of surface.

Adult↗

PubMed1979

["Emitted" cerebral activity and attention processes in a group of schizophrenics. 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 sommation 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↗

PubMed1995

Auditory and visual evoked potentials in individuals with organic and cultural-familial mental retardation.

Brainstem, middle-latency, and long-latency auditory evoked potentials (BAEPs, MAEPs, and LAEPs) and visual evoked potentials (VEPs) were recorded from subjects without mental retardation (control subjects) and from subjects with organic mental retardation or cultural-familial mental retardation. Both mentally retarded groups had smaller mean VEP amplitudes and longer mean LAEP latencies in response to target stimuli than did the control subjects, showing that the target stimuli were evaluated more slowly by the subjects with than by those without mental retardation. We found no significant differences between the mentally retarded and control groups with regard to BAEPs or MAEPs, and the two mentally retarded groups did not differ significantly in any EP parameter. The implications of these results for the defect and developmental theories of mental retardation were discussed.

Adolescent↗

PubMed1993

Pattern visual evoked potentials in cases of ambiguous acuity loss.

Thirty patients were referred to our visual evoked potential laboratory with complaints of profound acuity loss in one or both eyes. However, the objective ophthalmologic findings were normal, including pupillary reaction, and anterior segment and fundus examinations. Transient visual evoked potentials to a 2.3-c/deg sinusoidal grating pattern were found to be present in 26 of these 30 patients. Visual evoked potentials may be used as a measure of afferent pathway integrity.

Adolescent↗

PubMed1999

Can interocular pattern reversal visual evoked potential and motor reaction time differences distinguish anisometropic from strabismic amblyopia?

PURPOSE: With the use of the pattern reversal visual evoked potential and the motor reaction time, we sought to differentiate anisometropic amblyopia from strabismic amblyopia on the basis of the visual transmission time. METHODS: Pattern reversal visual evoked potentials and motor reaction times were obtained in nine normal subjects, eight anisometropic and seven strabismic amblyopes. RESULTS: Our results show that while the peak time of the pattern visual evoked potential in anisometropic amblyopia and strabismic amblyopia was significantly delayed, it could not distinguish the two types of amblyopia. In contrast, a significantly longer interocular increment in strabismics compared to anisometropes was found with the reaction time, but not with the pattern visual evoked potential. CONCLUSION: Our findings thus show that it is possible to distinguish strabismic from anisometropic amblyopes using interocular differences in reaction time measurements. Our results bring support to the contention that the two types of amblyopia represent different neural abnormalities.

Adult↗

PubMed1999

Abnormal visual evoked potentials in children with "Alice in Wonderland" syndrome due to infectious mononucleosis.

Visual illusions characterized by distortion of form, size, reciprocal position of objects, movement, or color, labeled as "Alice in Wonderland" syndrome, were discussed in children with infectious mononucleosis, as well as in other clinical conditions, such as migraine, epilepsy, use of certain hallucinogenic drugs, etc. The purpose of our study was to investigate for the first time visual evoked potential results in children with "Alice in Wonderland" syndrome associated with infectious mononucleosis. Five children with "Alice in Wonderland" syndrome associated with infectious mononucleosis underwent visual evoked potential studies during and after their clinical symptoms. Visual evoked potential results during the disease demonstrated statistically significant high amplitudes of P100-N145 in all children compared to the control group. A few weeks later, repeated studies after the resolution of the complaints were normal. Since the same findings can be observed in patients with migraine, we postulate that a common pathophysiologic underlying abnormality, which can cause transient focal decreased cerebral perfusion, could be involved in the disease process of these two conditions.

Adolescent↗

PubMed2003

Effect of haemodialysis on visual-evoked potential parameters.

Different papers have emphasized the presence of visual-evoked potential (VEP) abnormalities in metabolic disorders. The aim of this study was to perform pattern VEP (PVEP) recordings in patients with chronic renal failure just before and 24 h after dialysis to test the effect of this procedure on visual pathway generated parameters. Twenty-four haemodialysis patients (M/F:14/10; mean age: 48.8 +/- 14.1 years) were examined. None of them were complaining from visual difficulties or from visual loss. The recording sessions were performed just before and 24 h after dialysis. The control group consisted from 27 healthy subjects matched for age and sex. Eight (33%) patients demonstrated abnormal P100 latency prolongation in at least one tested eye (six patients in one tested eye, two in both eyes) in the recording session just prior to dialytic treatment. In the post-treatment session, it was found that the abnormal P100 latencies that were present in six patients (75%) before dialysis had returned to normal, while in the remaining two (25%), the latency abnormality persisted. No correlation was found between VEP parameters and dialysis duration, serum blood urea nitrogen (BUN), creatinine, parathyroid hormone and haematocrit levels. However, a positive correlation in the intradialytic percentage variation of bodyweight with P100 latencies was found. Visual evoked potential is a reliable, simple and non-invasive technique that can be used for the investigation and follow up of subclinical involvement of visual pathways in patients with chronic renal failure. Detected abnormalities in some uraemic patients are reversible by using dialysis.

Adult↗

PubMedDate not supplied

Motion-onset visual evoked potentials improve the diagnosis of glaucoma.

Chronic glaucoma has been shown preferentially to damage larger retinal cells and optic nerve fibres that provide the input to the magnocellular visual pathway. We compared the motion-onset visual evoked potentials (primarily the magnocellular system) with those to standard pattern reversal in 20 patients with bilateral chronic glaucoma. For motion-onset visual evoked potentials, the pattern (isolated 40' checks of 10% contrast) moved in four cardinal directions (varied randomly from trial to trial) at a velocity of 10 deg/s for 20 ms, with an interstimulus interval of 1 s. In pattern-reversal stimulation, the checkerboard reversed at a rate of 2 reversals per second. In 60% of the eyes investigated, the results of both types of visual evoked potentials correlated, showing either normal (27.5%) or increased (32.5%) latencies. In the remaining 40% of the eyes, the normal pattern-reversal visual evoked potential latencies were accompanied by prolonged motion-onset visual evoked potentials. The high occurrence of delayed motion-onset visual evoked potentials in our patients confirms the primary magnocellular loss in chronic glaucoma and suggests that the motion-onset VEPs are suitable for detection of glaucomatous changes.

Adolescent↗

PubMedDate not supplied

Relationship between visual evoked potentials and subjective differences between emotional expressions in "face diagrams".

The relationship between visual evoked potentials resulting from substitution of one image of a human "face diagram" for another and assessment of perceived differences between the emotional expressions of these faces were studied. Emotions were altered by changing the curvature of the mouth and/or the slope of the brows. Unlike the traditional approach, in which visual evoked potentials are recorded in response to presentation of a single stimulus bearing a face image, visual evoked potentials in the present study were recorded as the response to instantaneous substitution of a reference stimulus with a test stimulus, and thus represented the direct response to the difference between the stimuli. A characteristic of this approach was the use of a series of functionally associated test stimuli, in which there was a monotonic increase in the difference between the test and references images in terms of the variable characteristics of the stimuli. Analysis revealed differences in the amplitudes of the P120, N180, and P230 peaks in leads O1, O2, P3, P4, T5, and T6, which demonstrated high levels of correlation both with a points-scale assessment of perceived differences between the emotional expressions of faces and with the physical (configurative) differences between images of the same faces as defined by the differences in the orientation angles of lines determining mouth curvature and brow angle. Responses were seen to differences between stimuli for both types of change in pairs of images, both going from reference image to test image and from test image to reference image. Changes in the interpeak amplitude of the P120-N180 potential in the temporal areas of both hemispheres provided the earliest electrophysiological measure of perceived differences between the emotional expressions of human faces. This suggests application of the spherical model for the perception of emotions to specify emotional facial expressions in terms of the activity of line orientation detectors.

Electroencephalography↗

PubMed1989

[The prognosis of the visual results of treating children with congenital cataracts based on visual evoked potentials].

Examination of visual induced potentials on reversible chess-pattern in 46 children with bilateral congenital zonular cataracts before and after surgical intervention has revealed correlation between these potentials and degree of lens opacification. After cataract extraction, positive dynamics of the potentials was observed in case of slightly opacified lenses and was absent in intensive lens opacification. The authors consider it reasonable to use visual induced potentials for prognosticating visual results after surgical treatment of bilateral congenital zonular cataracts, this being of particular importance for early surgical interventions.

Cataract↗

PubMed2004

A sequential study of visual evoked potential in patients with vitamin B12 deficiency neurological syndrome.

OBJECTIVE: Visual pathways are vulnerable to vitamin B(12) deficiency but there is paucity of studies evaluating visual evoked potential (VEP) changes following vitamin B(12) supplementation. Our aim was to evaluate the visual evoked potential changes in patients with vitamin B(12) deficiency neurological syndrome and their changes after vitamin B(12) therapy. METHODS: Seventeen patients with vitamin B(12) deficiency neurological syndromes diagnosed on the basis of megaloblastic bone marrow or low serum vitamin B(12) level or both were subjected to testing of visual acuity, field of vision, colour vision and neurological examination. Cranial magnetic resonance imaging was done in 9 patients and pattern reversal VEP was carried out on admission. P(100) latency and amplitude were measured. Visual function and VEP studies were repeated at 3 and 6 months after vitamin B(12) therapy. RESULTS: The patients' age ranged between 17 and 69 years; 7 were females and 16 were lactovegetarians. The duration of symptoms ranged between 10 days and 10 years. Visual acuity, colour vision, field of vision and fundus oculi were normal. VEP revealed prolongation of P(100) latency in 10 patients (17 eyes) which was mild in 2, moderate in 10 and marked in 5 eyes. Six months after treatment, P(100) latency improved to normal in all except 4 eyes. VEP abnormality was related to duration of illness and antiparietal cell antibodies. CONCLUSIONS: VEP is frequently prolonged in patients with vitamin B(12) deficiency neurological syndrome although asymptomatic. It usually returns to normal after treatment.

Adolescent↗

PubMed1988

Retinocortical conduction time in diabetics with abnormal pattern reversal electroretinograms and visual evoked potentials.

Clinically evident retinal vascular disease in patients with diabetes mellitus may be preceded by an increase in visual evoked potential latency in electrophysiologic testing. This increase may indicate either retinal or optic nerve dysfunction. To determine the origin of the latency increase we initiated a cross-sectional study of simultaneous pattern-reversal electroretinograms and visual evoked potentials. We recorded transient (3.8 reversals/second) pattern electroretinograms and visual evoked potentials using both 15' and 60' high-contrast black-white checks. Fifty-five diabetic patients (34 with no retinopathy and 21 with background retinopathy) and 34 age-matched visual normals (controls) were tested. Group data in diabetics showed significant latency increases in both tests, but not significant differences in retinocortical conduction time were noted. These results suggest that the increases in visual evoked potential latency exhibited by diabetic patients with little or no retinopathy usually reflect altered retinal function rather than optic neuropathy. Two patients with background retinopathy exhibited retinocortical conduction times that exceeded the normal mean by more than two standard deviations, suggesting that optic neuropathy may occasionally occur in diabetic patients with background retinopathy.

Adult↗

PubMed1981

Visual evoked potentials in chiasmal gliomas in four adults.

Visual evoked potentials (VEPs) were recorded from four patients with surgically verified chiasmal gliomas. Despite good visual acuity, 6/12(20/40) or better in each eye, these patients showed substantially reduced VEP amplitudes to a diffuse flash stimulus and hardly detectable responses to a highly textured checkerboard-pattern stimulus. The dissociation between evoked electrical activity and visual acuity is noteworthy; this differs from previously reported findings in patients with extrinsic compressing lesions of the chiasm or with lesions of demyelinating disease, which usually reduce VEP amplitude and increase conduction time in rough proportion to a loss of visual acuity.

Adult↗

PubMed1988

[Comparative study of visual evoked potentials and magnetic resonance imaging in multiple sclerosis].

19 patients with clinically definite, probable or possible multiple sclerosis were examined by means of visual evoked potentials and magnetic resonance imaging. The patients were classified in three groups according to the criteria of Mac Alpine. 11 patients had definite multiple sclerosis: 8 of these patients, who had visual disorders evoking an optic neuropathy, had abnormal visual evoked potentials and 7 of these 8 patients had a pathological magnetic resonance imaging. In the other 3 patients of this group without optic neuropathy. 2 of them had abnormal visual evoked potentials and the 3 had a pathological magnetic resonance imaging. Two patients had probable multiple sclerosis, one of them had abnormal visual evoked potentials and a pathological magnetic resonance imaging. Finally, 6 patients had possible multiple sclerosis, one had a optical neuropathy, with abnormal visual evoked potentials but with a normal magnetic resonance imaging. Among the 5 other patients, 2 had abnormal visual evoked potentials and a pathological magnetic resonance imaging. The results obtained in comparison with the other reported in the literature show that magnetic resonance imaging brings a certain number of criteria which when associated with visual evoked potentials seem to be a further development in the diagnosis of the affection. However, despite of the existence of correlations, the lack of specificity of the lesions found with magnetic resonance imaging should lead the clinicians to a cautions optimism.

Adolescent↗

PubMed1994

Influence of simultaneous pattern-reversal electroretinogram recording on visual evoked potentials.

Little is known about the influence of the presence of a gold-foil electrode on pattern-reversal visual evoked potential recording, although simultaneous pattern-reversal electroretinography has been applied in several clinical investigations. We compared the results of pattern-reversal visual evoked potentials simultaneously recorded with pattern-reversal electroretinograms with those obtained during separate pattern-reversal visual evoked potential recording in 10 normal subjects. Transient response (reversal rate, 1 Hz; check size, 30') and steady-state response (reversal rate, 5 Hz; check size, 120', 60', 30', 15' and 7.5') were analyzed under the stimulus contrast condition of 90%. Neither P100 latency in transient responses nor amplitudes in steady-state responses exhibited significant change at any check size when they were recorded separately or simultaneously with pattern-reversal electroretinograms. The results suggest that the gold-foil electrode exerts no significant influence on pattern-reversal visual evoked potentials. Simultaneous pattern-reversal electroretinogram and visual evoked potential recording is therefore confirmed to be a clinically useful method. This procedure makes the synchronous recording of both responses possible under the identical stimulus conditions.

Adult↗

PubMedDate not supplied

Visual evoked potentials in humans during recognition of emotional facial expressions.

Visual evoked potentials were recorded from the occipital, parietal, central, frontal, and posterior temporal areas of the cortex during recognition of emotionally positive, negative and neutral facial expressions and during passive observation in 22 right-handed healthy subjects. These studies showed that in the posterior temporal areas, the latencies of the N90, P150, and N180 waves of potentials evoked by faces with emotionally negative expressions were significantly shorter than those evoked by other types of facial stimuli. Differences were seen both on recognition and during passive observation. Correct recognition involved both hemispheres and was characterized by high levels of interhemisphere temporal correlation of the processes occurring during the development of the P150 wave in the posterior temporal and the N180 wave in the frontal parts of the cortex. The possible relationship of these data to primary subthreshold recognition of facial expressions in the posterior temporal fields of the cortex is discussed, as is the role of the frontal cortex in completing this process and in taking the correct decision about the nature of the image.

Adult↗

PubMed1984

Hemispheric asymmetry of visual evoked potentials in patients with well-defined occipital lesions.

Visual evoked potentials were examined in 3 patients who had well defined unilateral occipital lobectomy. In an attempt to resolve discrepancies in the interpretation of hemispheric asymmetries in evoked potentials, recordings were obtained from a wide array of electrodes with multiple montages during full-field and hemi-field stimulation with checkerboard pattern reversal and during full-field flash stimulation. The discrepancies appear to be due primarily to differences in electrode montages used in recording. The use of a midfrontal reference electrode reliably produces a paradoxical EP lateralization: abnormal EPs are recorded over the intact occipital lobe and normal EPs are recorded over the ablated occipital lobe. These findings are fully consistent with the interpretation of Barrett et al. (1976) that the generator of the P100 has an equivalent dipole located in the calcarine cortex on the posteromedial surface of the contralateral hemisphere. Our findings support the use of the Queen Square montage (Halliday et al. 1977). The use of electrodes at O1 and O2 referred to the ipsilateral earlobe yields inconsistent lateralization and should be discouraged. The lateralization of EP abnormalities did not differ for flash and pattern reversal, although the asymmetries were sometimes more prominent with pattern reversal.

Brain↗

PubMed1987

Delayed visual evoked potentials are independent of pattern orientation in macular disease.

Visual evoked potentials (VEPs) and contrast sensitivity (CS) were studied in patients affected by maculopathy. VEP delays and CS reduction were demonstrated in each affected eye. In distinction to patients affected by multiple sclerosis (MS), in maculopathy patients VEP latency is independent of the orientation of the grating stimulus. It is proposed that stimulating with more than one pattern orientation is useful in the differential diagnostic use of VEPs.

Adult↗