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PubMed1987

Usefulness of different stimuli in visual evoked potentials.

The goal of this study was to determine the relative usefulness of the flash (FL), pattern reversal (PR) of 56', and PR of 28' in 62 patients (pts) with either MS (34) or non-MS (28) compared with normals (19). An abnormal visual evoked potential was found in 58%, 69%, and 81% of the eyes tested in possible, probable, and definite MS and in 88% of the non-MS group. The 28' PR produced the most abnormal responses, the greatest number with either greater than 3 standard deviations (SD) from the mean or greater than 2 SD in both MS and non-MS groups. The FL was second best at producing the most abnormal responses, but more often produced the only abnormality (29), compared with 28' PR (11). The 56' PR produced the only abnormality in none of the MS pts and in only one of the non-MS pts. In all categories (most abnormal, greater than 3 SD, greater than 2 SD, the only abnormality of greater than 3 SD or greater than 2 SD, and other peaks abnormal), the 28' PR was usually by far the best stimulus for definite (and probable) MS, but equally as effective was the FL in the possible MS pts Our data suggest the usefulness of 28' and not 56' PR, but the FL is especially useful in pts with possible MS.

Adolescent↗
PubMed1987

Amplitude difference between pattern-evoked potentials after left and right hemifield stimulation in normal subjects.

The amplitude of visual evoked potentials (VEPs) to pattern hemifield stimulation was measured in 14 normal right-handed subjects. The paired t test was used to determine if the values differed between right and left hemifield stimulation. The amplitude of transient VEPs from a midoccipital electrode and a lateral occipital electrode ipsilateral to the hemifield stimulated was significantly greater with right hemifield stimulation. This result is compatible with neuroanatomic asymmetries of human striate cortex. Amplitude distribution over the scalp was markedly different between transient and steady-state VEPs that probably reflect activities of different populations of cortical neurons.

Adult↗
PubMed1999

The effect of check size on VEPs in healthy humans: a parabolic relationship between check size and N145 wave.

The effect of check size on pattern reversal VEPs was examined in healthy adult volunteers. The subjects were exposed to full-field binocular stimulation. Five checkerboard patterns with check sizes 13', 25', 50', 75' and 100' were used as the visual stimuli. The patterns reversed at a rate of 1 reversal/sec. Well-defined pattern reversal VEPs were obtained for all check sizes in all subjects. As the check size increased a transition from a triphasic to an almost monophasic wave form was observed. N75 and P100 amplitudes, together with N75 latency, revealed linear relationships with check size; the N145 amplitude displayed a parabolic relationship with check size. No significant relationships were found for P100 and N145 latencies. It is concluded that the N75 wave originated mainly from the activity of the foveola, whereas the more eccentric regions contribute more to the formation of P100, and the interaction of both regions elicited the N145 wave.

Adult↗
PubMed1993

Complex spike responses of cerebellar Purkinje cells to constant velocity optokinetic stimuli in the cat flocculus.

In the cat cerebellar flocculus without cerebrum but with intact accessory optic tract, complex spike (CS) responses to horizontal optokinetic stimuli (velocity-step at 2 degrees/s) were investigated. The directionally selective CS responses were present only during the short-duration stimuli but not during the continuous unidirectional stimuli. Following the end of the stimuli during the stationary surround phase, the CS activity was modulated in a manner opposite to the preceding CS response during the stimulation. These CS responses cannot simply be interpreted as sensory responses to the retinal slip input; they may in fact be deeply associated with the motor control command of the eye movement which would be elicited by the retinal slip.

Animals↗
PubMed1988

Colour-black pattern reversal visual evoked potentials (colour-black-PVEPs): neurobiological aspects and clinical applicability of a new method.

The new method of Colour-Black-PVEPs was applied to 67 healthy subjects with normal colour vision who were subdivided into age groups (= AG) I (N = 40: 18-30 years) and AG II (N = 27: 31-60 years): 1. For the N80-, P100- latencies and the N80P100-amplitudes of all Colour-Black-PVEPs we obtained age-, sex- and eye-matched normative data. 2. The female subjects of AG I showed shorter (p less than or equal to 0.05 resp. 0.002) P100-latencies and higher (p less than or equal to 0.02 resp. 0.0001) N80P100-amplitudes in the Colour-Black-PVEPs than the male subjects. In AG II, however, the Colour-Black-PVEPs did not show any more sex-differences for the P100-latencies, whereas the N80P100-amplitudes remained significantly higher for the females. 3. In the Colour-Black-PVEPs the N80- and P100-latencies did not reveal age-dependent changes. The N80P100-amplitudes, however, decreased with increasing age, but this was significant for the females only. 4. The head sizes, although decreasing with age, were in both age groups significant smaller for the females only. 4. The head sizes, although decreasing with age, were in both age groups significant smaller for the females. Therefore, head size alone could not fully explain the sex-differences in the Colour-Black-PVEPs and their age-dependent changes. 5. In both age groups, the N80--and P100-latencies increased significantly for both sexes from the Green-Black- and Red-Black-PVEPs to the Blue-Black-PVEPs. The N80P100-amplitudes decreased in the same sequence. This method may become a valuable tool in the investigation of neurophysiological and ophthalmoneurological aspects of human colour vision.

Adolescent↗
PubMed1989

The visual evoked potentials to the light emitting diode compared to the flash and pattern reversal stimulus.

Light-emitting diode (LED), flash (FL) and pattern reversal (PR) stimuli were used to elicit visual evoked potentials (VEPs) in 16 normal subjects (32 eyes) and 39 patients (78 eyes) with signs of visual system abnormality. Latencies and amplitudes (plus standard deviations) of 5 components of each response, correlation coefficients of the normal and abnormal responses and false negatives and positives are presented for the 3 kinds of stimuli. The data show that responses to LED stimuli are very similar to those of FL stimuli and should be useful in the operating room to monitor the visual pathways, if various endogenous factors known to affect late responses can be stabilized.

Adolescent↗
PubMed2001

[Assessment of visual function before and after macular surgery by pattern visual evoked cortical potentials].

PURPOSE: To investigate pre- and postoperative visual function in patients with macular hole and those with epiretinal macular membrane (ERM) by means of visual evoked cortical potential (VECP). MATERIAL AND METHODS: VECP was recorded from 15 eyes with macular hole and 9 eyes with ERM prior to and 3 months after surgical treatment. Check sizes of 30' for transient stimulation, and 7.5', 15', 30', 60' and 120' for steady-state stimulation were applied. RESULTS: In transient VECPs, the P 100 component was prolonged and attenuated in both diseases before surgery, and it remained unchanged after surgery. In the eyes with macular hole, the amplitudes of steady-state VECPs showed significant reduction in 15' and 30' check sizes before surgery, and recovered only in 15' check size after surgery. The preoperative spatial frequency curve of ERM was lowered in the whole frequency range measured. CONCLUSIONS: VECP reflected the area of macular hole and ERM. VECP changes after surgery were considered to depend on the degree of surgical invasion.

Evoked Potentials, Visual↗
PubMed2001

Normalization models applied to orientation masking in the human infant.

Human infants can discriminate the orientation of lines within the first week after birth (Atkinson et al., 1988; Slater et al., 1988) but have immature orientation-selective pattern masking until after 6 months of age (Morrone and Burr, 1986). Here the development of orientation processing is further examined using a visual-evoked potential paradigm and normalization models of pattern masking. Contrast response functions were measured for 1 cycle per degree (cpd) gratings, counterphase-reversed in contrast at either 3.3 or 5.5 Hz. A second 1 cpd, 20% contrast, 8.3 Hz grating of either the same or orthogonal orientation was added as a mask. Evoked responses associated with the test grating, the mask, and intermodulation between the two were individually extracted using spectral analysis of the scalp-recorded EEG. Adults exhibited orientation selectivity in the masking of their test component responses and in nonlinear intermodulation between the test and mask stimuli. Infants <5 months old, however, demonstrated nonselective masking or a reversed selectivity in their responses to the test component, with adult-like orientation selectivity in their intermodulation responses. Within the context of a normalization model of pattern masking, the results are consistent with the existence of oriented filters early in life the responses of which are normalized immaturely until approximately 5 months of age.

Adult↗
PubMed2002

Study of the visual evoked magnetic field with the m-sequence technique.

PURPOSE: Multifocally stimulated visual evoked magnetic field (VEF) examination with an m-sequence technique (multifocal VEF; mVEF) was studied, and the neural generators at peaks of mVEF were estimated in the visual cortex. METHODS: Visual field stimulation was generated by a multifocal testing system with use of the m-sequence technique. The stimulation pattern covered a central area extending from 0.6 degrees to 10 degrees in radius outward from the center of four visual-field quadrants. The stimulation pattern was projected onto a screen by a liquid crystal projector. VEFs of 14 healthy adults were recorded with a 160-channel, whole-head-type magnetoencephalography (MEG) system. The output signals of 16 selected MEG sensors covering the occipital region were recorded for each subject with the multifocal testing system, and the second-order responses were calculated. The analyzed response data files were transferred to the MEG system, a single equivalent current dipole (ECD) was estimated to locate the neural generator, and the localization was superimposed onto the corresponding brain magnetic resonance image of the subject. RESULTS: mVEFs showed three peak waves (N75m, P100m, N145m) in 75% of the subjects and two peak waves (N75m, N145m) in 25%. (N, P and m denote negative, positive, and magnetic fields, respectively.) Latencies of the first and the last peak were similar between the two kinds of peak waves. ECD examination showed more than 97% of goodness of fit at all peaks, and the relation between EDCs and the stimulated visual field coincided with a retinotopic organization that fit a cruciform model in all subjects. ECD depths from the occipital pole were similar to the depth expected from the human linear cortical magnification factor model in all subjects. Main neural generators of all mVEF components (N75m, P100m, N145m) were shown in the striate cortex (V1). CONCLUSIONS: Testing the VEF with an m-sequence technique showed stable responses to simultaneous stimulation of four visual-field quadrants. Consistency of correlation of the estimated ECD with the known cortical organization of the primary visual cortex confirmed the reliability of this examination. The three mVEF peaks were thought to derive mainly from V1 activity.

Adult↗
PubMed2003

Development of the spatial organization and dynamics of lateral interactions in the human visual system.

Psychophysical thresholds and neuronal responses for isolated stimuli are strongly modified by nearby stimuli in the visual field. We studied the orientation and position specificity of these contextual interactions using a dual-frequency visual-evoked potential technique in developing human infants and adults. One set of small, oriented stimulus elements (targets) was tagged with a temporal frequency f1 of 4.52 Hz. The addition of an abutting second set of similar patches (flankers) tagged at f2 = 2.58 Hz had three effects: (1) The flankers reduced the second and fourth harmonic responses to the targets. This reduction was independent of flanker orientation or position and age. (2) The response to the combination of targets and flankers also contained nonlinear interaction terms (1f1 +/- 1f2) that were tuned for flanker orientation and position in adults, but only for flanker orientation in infants 8-31 weeks of age. (3) Nonlinear interaction terms recorded at 2f1 +/- 2f2 were large and untuned for flanker orientation and position in adults but were nearly absent in the youngest infants. The three forms of nonlinear interaction, thus, have differences in sensitivity to flanker orientation and position and differential growth trends, indicating that they are generated by different mechanisms. These three forms of interaction could serve different functional roles. The first process provides a nonselective gain control that is fully functional in early infancy. The second process, which develops slowly, is selective for the specific form of the stimuli. The third process, which is also immature, pools across orientation.

Adolescent↗
PubMed2006

[Comparison of objective assessment using the sweep pattern visual evoked response acuity (SPVERA) and illiterate E visual acuity].

OBJECTIVE: To compare the vision objectively assessed by SPVERA with the illiterate E Acuity in normal subjects. METHODS: The effect of artificially induced image defocusing on visual acuities (Vas) measured by SPVEP and illiterate E chart measurement was studied in 14 normal subjects. SPVEP was recorded using vertical gratings of 8 different spatial frequencies ranging from 0.235 9 to 30.203 2 c/deg. The responses were averaged and displayed through the discrete Fourier transform on the monitor display. SPVERA was determined by extrapolating the PVER amplitude -spatial frequency function to baseline. SPVERA was compared with illiterate E visual acuity measured under the same conditions of optical defocus. RESULTS: With moderate defocusing (<+1.0 diopter (D),VA > 0.42), the SPVERA were equal to or poorer than the illiterate E visual acuity. With more defocus (> +2.0 diopter (D), VA < 0.3),the SPVERA became better than the illiterate E chart Visual Acuity. The correlation between the two acuities was r2 = 0.919. CONCLUSION: SPVERA and the illiterate E visual acuity correlated to a certain degree. We conclude that the SPVERA is effective in estimating vision objectively.

Adult↗
PubMed1991

[Primary color P-VEP in diabetic retinopathy].

148 normal eyes and 123 eyes of diabetic retinopathy patients were examined the red, green, blue primary color and black/white P-VEPs, with the conclusion that the latencies of P100 were significantly delayed in the diabetic group, particularly that of the blue color, which was also in positive correlation with the level of blood sugar and the duration of diabetes. The consistency of blue P-VEP with fluorescein angiographic examination in diabetic retinopathy was good, and the abnormality ratio of the former (73.0%) was higher than that of the latter (60.2%). The results indicated that S-wave cones were damaged more readily than were L-wave cones, and the blue P-VEP was sensitive in monitoring the injury to visual function in diabetes.

Adult↗
PubMedDate not supplied

The evaluation of sellar region tumours with pattern visual evoked potentials.

Pattern visual evoked potentials (PVEPs) were performed on 20 patients with sellar tumours. The aim was to assess the validity of full-field PVEPs combined with a topographic recording in chiasmatic compression. They were abnormal in 95% of the patients, with variable patterns (absent or distorted responses). Our results show that PVEPs are very sensitive in revealing compression on visual pathways and that they correlate with the progression of the tumour. However, they are not reliable in detecting the chiasmatic or retrochiasmatic site of the lesion and relative visual field defect, because of the multidirectional extension of the tumour.

Adult↗
PubMed1989

Retinocortical time exhibits spatial selectivity.

We recorded simultaneous electroretinograms and visual evoked potentials to pattern-reversal stimulus in ten normal subjects employing check sizes subtending 7.5, 15, 30, 60, 120, 240 and 480 min of visual arc. The mean peak latency of the pattern electroretinogram (PERG) b wave decreased logarithmically with increasing check size. The mean peak latency of the pattern visual evoked potential (PVEP) P100 component was shortest for 30 min check size and was longer at both smaller and larger check sizes, a phenomenon termed spatial selectivity. Retinocortical time (RCT) was calculated as the latency difference between the PVEP P100 peak and the PERG b wave. The RCT also exhibited spatial selectivity similar to that of the PVEP P100 component; mean RCT was shortest for 30 min check size and was longer at both smaller and larger check sizes. Implications are discussed in light of our current knowledge of the origins of the PERG and PVEP and visual processing of pattern-reversal stimuli. Simultaneous recording of PERGs and PVEPs in patients with disease of the afferent visual pathways employing a large range of check sizes may increase the diagnostic sensitivity of visual electrophysiologic testing.

Adult↗
PubMed1988

Brain potentials associated with pattern displacement and saccadic eye movements in humans and rhesus monkeys.

Visual evoked potentials (VEPs) to the onset of motion of visual patterns and brain responses associated with saccadic eye movements (SRPs) were compared in human subjects and in rhesus monkeys. Three different velocities of pattern motion were employed. In humans, brain responses were recorded from six scalp areas. In monkeys, transcortical recordings were obtained from chronically implanted electrodes in the occipital, temporo-parietal, and frontal areas. In humans there was a clear difference in VEPs to the pattern motion between the anterior (Fz, Cz) and posterior (Pz, Oz) scalp regions. The earliest component was a positive peak at 85 ms at Oz followed by a negativity around 110 ms. In the fronto-central leads the VEP was characterized by a negativity at 145 ms and a subsequent broad positive component around 250 ms. SRP responses differed in the early components from the VEPs to pattern motion but a good correspondence was found in the morphology of the late components of the two types of brain potentials. Furthermore, flashed-on VEPs and SRPs elicited a late positivity of more pronounced amplitude than VEPs to pattern displacement. In monkeys similar findings were found: an early negative component of the pattern-displacement VEP could not be observed in the SRP responses over the visual cortex while the late portion of the SRP waveform was greater than the late positivity of the VEP to motion-onset.

Adult↗
PubMed1986

A new method to measure the pattern reversal visual evoked response in infants and young children.

A modification was made of the conventional method of recording the pattern reversal visual evoked response (VER) to study the VER in infants and young children. Application of this modified method to 36 patients, the majority of them with retinopathy of prematurity, showed that this method is useful in the evaluation of the visual function in infants and young children, and also in a 12-year-old mentally retarded girl.

Child↗