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At least 145 records · Page 8Linked to original sources
PubMed1983

Abnormal evoked potential latencies in amblyopia.

The latency of the first (P1) and second (P2) major positive waves of the pattern reversal visual evoked potential (VEP) for small checks (15 minutes of arc) was measured in 68 visually normal children and 32 amblyopic children with mild to moderate visual acuity losses. In the normal children there were no P1 and P2 interocular latency differences. The amblyopic children showed longer P1 latencies and shorter P2 latencies in their amblyopic eye than their normal fellow eye. These findings can be accounted for by a selective loss of the contrast-specific evoked potential mechanisms in amblyopia. The 'shorter' P2 latency obtained from amblyopic eyes for small checks is a reflection of the luminance responses that are normally elicited by larger (60 minute) checks.

Amblyopia↗
PubMed1989

Pattern-reversal visual evoked potentials in normal 7- to 15-year-old twins: a correlation analysis.

Pattern-reversal visual evoked potentials (PRVEPs) were tested in 11 sets of monozygotic (MZ) twins and 22 sets of dizygotic (DZ) twins matched on age, sex and educational level. They ranged in age from 7 to 15 years. The PRVEPs of MZ twins exhibited a significantly greater degree of similarity than those of DZ twins. The peak latencies and amplitudes of PRVEP components obtained from MZ twin pairs were significantly correlated. The correlation coefficients for the peak latencies of the P2 (or P100) component were the only ones to differ significantly between the DZ twins of the same sex and DZ twins of opposite sexes. These coefficients, obtained using PRVEPs, were much greater than those obtained with flash visual evoked potentials.

Adolescent↗
PubMed1996

Processing visual evoked potentials based on matched filtering of single trial responses.

Physiological signals recorded after presentation of a stimulus can be considered as the sum of an evoked sensory response and uncorrelated noise corresponding to the spontaneous neural background activity. In case of low signal-to-noise ratio, the sensory signal is estimated by averaging a large number of single trial records sampled under the same experimental conditions. The averaging technique, however, is inappropriate for displaying trial-to-trial variations that may occur during a recording session. A method based on matched filtering was developed for processing single visual evoked potentials (VEPs). To illustrate the performance of this method, a set of VEPs for grating patches of 8 different contrasts (including 0) was evaluated. The VEPs were subjected to signal detection analysis by computing for each contrast similarity indices between the single trial records and the averaged response used as a template. The signals were analysed in terms of probability density distributions, expressing the goodness of fit between template and each single waveform.

Cluster Analysis↗
PubMedDate not supplied

Prognostic value of visual evoked responses in childhood amblyopia.

We assessed the possible clinical utility of pattern reversal visual evoked potentials in predicting the success of pleoptic treatment. Thirty amblyopic children--16 strabismic, 11 anisometropic and three of refractive type (in all cases the amblyopia was monocular)--and ten children without amblyopia (control group) were examined by conventional psychometric methods. Visual evoked potentials (VEP) to pattern reversal stimulation were also recorded. The amblyopic group was treated with occlusion of the preferred eye for three to six months. Psychometric and VEP tests were repeated in 15 amblyopic children after the treatment. The pre-treatment VEP amplitude side-differences (between amblyopic and better fellow eye) were significant, with first positive wave, P1, being invariably lower on the amblyopic side. We correlated the side-differences in visual acuity with the corresponding side-differences in amplitude and latency of the P1 wave. In the former the correlation coefficient was r = 0.47 (p < 0.01), and in the latter r = 0.65 (p < 0.01). Latency was prolonged in the eyes with significantly reduced visual acuity in which the wave form was also typical for amblyopia. We then correlated the difference between pre- and post-treatment visual acuity of the amblyopic eye with the pre- and post-treatment difference in amplitude (correlation coeff. r-0.51 (p = 0.05)) and latency of the P1 wave (correlation coeff. r = 0.40 (p > 0.05)).(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1988

Visual evoked potentials in elderly patients with primary or multi-infarct dementia.

Flash and pattern-reversal visual evoked potentials (VEP) were recorded in 35 elderly patients with dementia, and 19 controls of equivalent age. Dementia produced a slowing of the major positive (P2) component of the flash VEP but did not affect the latency of the flash P1 component or the P100 pattern-reversal component. This unusual type of abnormality was found in both primary and multi-infarct types of dementia, and has previously been found in primary presenile dementia. The results show that the VEP can be used for the diagnosis of multi-infarct, and primary presenile and senile dementias.

Aged↗
PubMed1991

Quantitative analysis of the cross-correlation between pattern ERG and pattern VEP.

The cross-correlation between PVEPs and PERG was investigated. (1) There were high correlations between PVEPs recorded from the inion and those from points Oz, Pz, Cz, and Fz in the range of 75-150 msec following pattern visual stimulation to the eyes although no correlation was found in the range 0-75 msec. (2) PVEPs recorded from the inion highly correlated with PERG in the 75-150 msec range but not in the 0-75 msec range. It suggests that the late negative component included in the PERG reflected the electrotonically spread at the eye level of PVEP. (3) Intra-individual reproducibility was studied. PVEPs showed a high reproducibility in the 75-150 msec range, but not in the 0-75 msec range. The reproducibility of PERG was high in the 0-75 msec range but also in the 75-150 msec range, where PERG reflected PVEPs. These results suggest that the early positive component of PERG was specific to the cell activities in the retina to the pattern visual stimulus, and had an origin different from the brain activity for PVEPs.

Adult↗
PubMed1990

[State and complexity-dependent symmetry identification of 2-dimensional patterns and evoked potentials].

To analyse the influence of structural complexity of visual patterns and of an operationally defined cognitive state on evoked potentials some on--line closed--loop experiments were carried out. Symmetrical checkerboard patterns generated by means of Walsh functions were used as stimuli. The inherent symmetry should be recognized by the subjects. The state was defined on the basis of the spectral power density distribution of the EEG measured in the time interval of one second before the stimulus onset. The two state values were labeled by the state of alpha wave dominance and the state of non alpha wave dominance. According to the definition for the state of alpha wave dominance 70% of the whole spectral power must be contained in the frequency range from 8 Hz until 13 Hz at least. Otherwise the prestimulus EEG are labeled by the concept of non alpha wave state. The influence of the cognitive state and of the structural complexity on the evoked potentials has been verified experimentally. Significantly higher amplitudes of the evoked potentials in the time range of 140 ms until 200 ms after stimulus onset are due to higher complexity of the stimuli. The state of alpha wave dominance led to significantly stronger negativity of the evoked potentials in the range of 280 ms until 400 ms after stimulus onset.

Arousal↗
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↗
PubMed1984

VEPs in humans reveal high and low spatial contrast mechanisms.

The effect of contrast on visual evoked potential (VEP) amplitude was examined in nine observers. A 6.0 cycles/deg (cpd) grating was modulated in an "on-off" mode at 7.5 Hz. The VEP response contains significant first and second harmonic components: their growth with contrast is parallel, each function consisting of two limbs. The data are consistent with the hypothesis that the pattern VEP obtained with "on-off" presentation may reflect the contributions of "low" and "high" contrast neuronal populations demonstrated in physiological studies of the primate.

Evoked Potentials, Visual↗