Pattern visual evoked potentials in treatment trials for optic neuropathy.
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Acute Disease↗
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Voluntary alteration of evoked potentials?
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Attention↗
Neuroelectric concepts: form-color classification.
Visual event-related potentials (VEPs) were recorded from the scalp of human observers who viewed an orthogonal stimulus set, consisting of four stimuli, each of which had two attributes: a form (circle or triangle) and a color (green or red). The stimulus set was represented by an a priori stimulus classification model, defined by positions (i.e., degrees of arc) on a unit circle that specified the relationships among the form and color features. An analysis of VEP deviation waveshapes (delta VEP: deviations around average VEP for each electrode) showed that the a priori unit circle model predicted morphologies of the delta VEP waveshapes, as well as the overall relationships between waveshapes obtained for the form and the color attributes. Further analyses demonstrated that individual delta VEP waveshapes for color and for form were located on the circumference of a unit circle at the positions (angle) specified by the a priori model. The studies show that formal modeling of the way humans classify stimulus attributes provides a quantitative and predictive model of the way VEPs become classified and organized according to psychological principles.
Adult↗
The human motion VEP as a function of size and eccentricity of the stimulation field.
A 'motion onset VEP' was elicited by the onset of a pattern drift. The amplitude of the most distinct wave (AN200) was determined on the following stimulation conditions: eccentricity, 0 to 23 deg; velocity. 1.5 to 16 deg/s; spatial frequency, 0.19 to 2.1 c/deg; and stimulation field size, 0.2 to 160 deg2, AN200 remained constant at any degree of eccentricity if stimulation field size, velocity, and spatial frequency were M-scaled according to Rovamo-Virsu's M-equations. AN200 decreased as a function of eccentricity if field size and velocity were kept constant (spatial frequency had minimal effect). The size of the cortical representation field (Sc) in this case varied with change in eccentricity (stimulation field size constant). In another experiment, it varied by change in stimulation field size (eccentricity constant). For both conditions, AN200 was proportional to log Sc.
Electrodes↗
Retinal and retinocortical times to pattern stimulation in amblyopic children.
In order to determine whether in amblyopes retinal conduction delays contribute to the cortical measureable delays in the visual evoked cortical potential (VECP), peak latencies of the pattern electroretinogram (ERG) are measured in amblyopic children. The results are compared with those of the normal fellow eyes and those of a healthy control group. Simultaneously the latencies in the VECP are recorded and the determination of the retinocortical times is performed. Statistically retinal b-wave (Q) and a-wave (P) of the pattern ERG of amblyopic eyes do not show significant delays of peak latency. In retincortical times, however, there are significant prolongations. During occlusion therapy retinocortical values of normal fellow eyes are also delayed in comparison with the control group. A pathological conduction delay of visual information on the retinal level up to the generators of the pattern ERG can thus be excluded in amblyopia. The total latency delay in the VECP of amblyopes consists solely in a prolongation of retinocortical times.
Adolescent↗
Detection duration thresholds and evoked potential measures of stereosensitivity.
Visual evoked potentials have been proposed by some researchers to be more useful than behavioral techniques to evaluate stereo performance in children and certain clinical populations. Stimulus duration detection thresholds, visual evoked potentials, and scalp electrical potential distribution maps to dynamic random dot stereograms were studied. A high degree of correspondence was found between visual evoked potential amplitudes and behaviorally determined detection thresholds. Upper field stimuli had higher detection thresholds and generated lower-amplitude visual evoked potential responses than did centrally presented stimuli. For the most eccentrically presented stimuli, lower detection thresholds were found for stimuli presented in the right visual field than the left visual field. This finding was consistent with the pattern of VEP responses to be lateralized, with higher-amplitude responses recorded over left-hemisphere sites. The study examined a proposal that the major negative component of the stereoscopic visual evoked potential originates in cortical area V1. The results failed to support the proposal and were consistent with the main negative component of the VEP being generated in V2, rather than V1.
Adult↗
The effect of spatial frequency and contrast on the latency in the visual evoked potential.
The latency in the visual evoked potential was measured at spatial frequencies of 2-12 c/deg in 10 subjects. The contrast levels of the sinuosoidal grating patterns were set at 1.5, 1.75, 2.0, 2.25, 2.5, 2.75 and 3.0 log units above each subject's contrast sensitivity threshold. Two factors were shown to influence the latency: suprathreshold contrast and, to a lesser extent, spatial frequency. The visual evoked potential latencies at contrast sensitivity threshold were extrapolated. These threshold latencies showed considerable variation with spatial frequency and between subjects. Therefore, the visual evoked potential latency cannot be considered a useful tool for estimating the contrast sensitivity function.
Adult↗
Visual evoked cortical potentials from transient dark and bright stimuli. Selective 'on' and 'off-pathway' testing?
The superior hemifields of five normal left eyes were stimulated by novel equal and opposite contrast pattern onset stimuli which were generated on a cathode ray tube. Patterns consisted of 144 discs, each subtending 60 min arc at the viewing distance of 40 cm and were separated by a distance equal to their diameter. Equal and opposite light changes were created by presenting the disc patterns with different luminance values on a uniform constant background (20 cd/m2). Transient visual evoked cortical potentials to the appearance and disappearance of the patterns were recorded separately and analysed. Significant amplitude differences between the responses to bright and dark stimuli were observed with light increment responses being 36-53% larger than the light decrement responses for pattern on-set and 54-80% larger for pattern off-set respectively. This finding is attributed to the difference in the input to the ON and OFF Parallel Pathways which are known to carry light increment and decrement information respectively, as well as differences in the metabolic and discharge rates of these pathways.
Adult↗
Topographical study of stereo-related potentials.
In order to estimate objectively binocular vision and especially stereopsis, random dot stereograms generated by a personal computer were used. Brain activity during stereopsis was topographically studied by visually evoked potentials (VEPs). The potentials evoked by binocular viewing of patterns without disparity, e.g. correlogram, were very similar to the potentials evoked from patterns with disparity, i.e. stereogram, as many authors have already indicated. To derive the stereo-related potentials from the VEP elicited by stereograms, the potentials evoked by correlograms were subtracted from the potentials evoked by stereograms, and the differences of topographical distribution between normal and stereoblind subjects were investigated.
Adult↗
Visual evoked potential evidence for parallel processing of depth- and form-related information in human visual cortex.
This paper describes the first of two complementary studies designed to identify and to investigate the properties and likely functional significance of independently generated components of scalp-recorded responses evoked by stationary patterns. These experiments compared the influence of various stimulus parameters, including site of stimulation, pattern form, nature of background field and several binocular and monocular depth cues on a single subject's visual evoked potentials. The results revealed the presence, inter alia, of two topographically distinct components with the following properties. The earlier component (C2), whose polarity depends on the stimulus location in the visual field, is: contour-specific; best evoked by discrete pattern elements, but not gratings, in the central few degrees of the visual field; insensitive to any depth cues. By contrast, the later (consistently) negative potential (LNP) is not dependent on the form of the stimulus and is larger for paracentrally (beyond 1.5 degrees) than centrally located stimuli. It is also selectively enhanced by both monocular and binocular depth-cue stimuli, including the simulated forward movement of a pattern relative to a steady textured background; a stimulus which evokes no C2. The respective response properties of these scalp potentials suggest that there is parallel processing of depth- and contour-related features of stationary stimuli in anatomically separate regions of the human visual cortex.
Cues↗
An "oblique effect" in the visual evoked potential of the cat.
An oblique effect was observed in the amplitude of the VEP recorded from area 17 of the cat. The ratio of the responses to oblique gratings compared with responses to horizontal and vertical gratings averaged 0.77. Orientation dependence was strongest at low spatial frequencies, unlike the effect found in primates.
Animals↗
Visual evoked potentials in ataxia telangiectasia.
Pattern reversal visual evoked potentials (VEPs) elicited in four patients with ataxia telangiectasia revealed normal results in two and absent responses in two. The pathogenesis of the VEP abnormalities is discussed. It is surmised that the VEP changes reflect progressive degeneration of the nerve fibres in the anterior visual pathway, as in Friedreich's ataxia.
Ataxia Telangiectasia↗
Simultaneously recorded retinal and cerebral potentials to windmill stimulation.
Visual evoked retinal and cerebral potentials were recorded to onset rotation of an isoluminant sectored disc. While the retinal potentials recorded to onset rotation closely resembled the electroretinogram to a checkerboard or stripe pattern of fixed element size, the visual evoked potential changed interindividually and intraindividually from a fast positive wave at high contrasts, velocities and number of windmill segments to a later negative component at low contrasts, velocities and windmill segments. With change in luminance, contrast, speed and extent of rotation field size and number of disc segments, the visual evoked potential was generally less affected than the electroretinogram.
Adolescent↗
Effect of experimental scotoma size and shape on the binocular and monocular pattern visual evoked potential.
A small experimental, central scotoma significantly attenuates the human pattern visual evoked potential. The steady-state pattern visual evoked potential was recorded from seven visually normal adults who viewed a reversing checkerboard with 24' checks and a central scotoma that varied in size and shape. We found that square scotomas had to be at least 3 x 3 degrees to significantly (p < 0.05) attenuate the pattern visual evoked potential. Receptor density has been shown to be greater along the horizontal meridian than the vertical meridian. We hypothesized that this results in greater cortical representation of the horizontal meridian than the vertical meridian and, therefore, the pattern visual evoked potential might be significantly attenuated by a smaller rectangular scotoma oriented along the horizontal meridian than along the vertical meridian. One dimension of the rectangular scotoma was fixed at either 1 degree or 3 degrees, while the other dimension was varied from 1 degree to 8 degrees. The threshold scotoma size that significantly (p < 0.05) attenuated the pattern visual evoked potential was a horizontal scotoma subtending 1 x 4 degrees and a vertical scotoma subtending 5 x 1 degree (vertical x horizontal). Meridional differences in cortical representation were not apparent to the larger scotoma series in which the fixed dimension subtended 3 degrees (3 x 2 degrees and 2 x 3 degrees). Further analysis of the data revealed that the apparent meridional difference for the 1 degree scotoma series was a function of data variability. The determinant of the PVEP amplitude was scotoma area, not orientation. Monocular and binocular threshold scotoma sizes were the same, which could be due to the level of binocular summation demonstrated by our subjects.
Adult↗
Monocular contribution to the peak time of the binocular pattern visual evoked potential.
The contribution of each monocular pathway to the timing of the binocular pattern visual evoked potential was assessed in situations where a significant interocular timing discrepancy was observed. Monocular and binocular pattern visual evoked potentials to 0.5 degree checks were recorded from normal subjects, normal subjects in whom one eye was blurred, patients with monocular amblyopia, and patients with resolved unilateral optic neuritis. Normal subjects showed facilitation, while suppression was evidenced in subjects with monocular blurring. In patients with amblyopia, the affected pathway had no effect on binocular pattern visual evoked potential latency, suggesting that the amblyopic eye was suppressed. In contrast, all patients with optic neuritis showed binocular averaging. Our results show that different forms of binocular interaction are evidenced in normal subjects, in amblyopia and in optic neuritis, and suggest that a comparative analysis of monocular and binocular pattern visual evoked potential peak times brings valuable information to the clinical evaluation that could be used to distinguish disease processes further.
Adolescent↗
Pattern electroretinogram and visual evoked potential amplitudes are influenced by different stimulus field sizes and scotomata.
The pattern electroretinogram and the visual evoked potential were recorded simultaneously with various stimulus fields and artificial scotomata of increasing sizes. In contrast to an earlier study, a smaller check size (20') and two stimulus field sizes (20 degrees x 20 degrees and 10 degrees x 10 degrees) for the scotomata were used. With a concentric decreasing stimulus field, a reduction of both the pattern electroretinogram and visual evoked potential was found. Both showed a simultaneous reduction of amplitudes, but, compared with the amplitude in the full field, the reduction was more extensive for the pattern electroretinogram at each test field size. This implies a greater contribution to the pattern electroretinogram from more eccentric retinal parts. An artificial central scotoma of increasing size in the 20 degrees x 20 degrees field had less influence on the pattern electroretinogram than on the visual evoked potential. The percentage amplitude loss of the visual evoked potential was more pronounced. The visual evoked potential was eventually abolished by a scotoma size from 10 degrees x 10 degrees upward, while the pattern electroretinogram was still registrable. When scotomata of similar size were introduced in a smaller (10 degrees x 10 degrees) field, percentage pattern electroretinogram and visual evoked potential amplitude losses were less separated than in a larger (20 degrees x 20 degrees) test field.
Adult↗
Measurement of contrast sensitivity function using pattern-reversal visual evoked responses.
In order to determine whether pattern-reversal visual evoked response (VER) can be used to measure contrast sensitivity function (CSF), we investigated the effect of change of contrast upon pattern-reversal VER. Contrast thresholds for VER were extrapolated in five spatial frequencies. The CSF curve obtained from the VER showed the inverted U-shape as the psychophysical CSF curve. However, the low frequency fall-off that is usually seen in psychophysical CSF was less evident in the electrophysiological CSF. The difference between the electrophysiological CSF and the psychophysical CSF increased along with the spatial frequency. Proper stimulus conditions would make this method of evaluation of CSF by pattern reversal VER useful in relatively young children in whom psychophysical tests cannot be performed.
Adult↗
An automated system for visual studies.
An interactive computer-controlled system is described that is used for visual studies including Visual Evoked Potentials in humans and animals and Visual Receptive Field recordings in animals. Visual stimuli are generated by a display system and the brain activity is monitored by microelectrodes (for animal recordings) and scalp electrodes (for human recordings). The signals are amplified, digitized, and stored. The software uses a response feedback algorithm for mapping the receptive fields. Initially random patterns are presented on a TV monitor and the neural response is recorded. Depending on the response to the pattern and the light distribution in it, the algorithm calculates a new pattern, always trying to maximize the response. As the process goes on, the stimuli patterns become near optimal and thus the receptive field of the neuron is mapped automatically, as a result that for many years has been formed by trial and error. The same system is used for analysis of the recorded results and recordings of the Visual Evoked Potentials in animals and humans. For the human evoked potentials different patterns are generated on the display monitor with a variety of choices, ranging from the simplest (checkerboard and gratings) to the most complicated ones (faces and scenes).
Animals↗