A first comparison of the human multifocal visual evoked magnetic field and visual evoked potential (original) (raw)
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Vision Research, 2009
MfVEPs were recorded with a 22 deg radius, 60-sector pattern reversal dartboard stimulus (VERIS) at 6 contrast levels (10, 25, 35, 50, 75, 95%). Contrast response functions (CRFs) based on response amplitudes were adequately described by a simple hyperbolic function. The effect of reducing contrast on the amplitude was most apparent in the central 1 deg radius, which had a C 50 (contrast at 50% of the maximum response) in excess of 50%, compared to values for C 50 in more eccentric regions that were 30% or lower. Mean latency increased 6 (± 0.7 SE) ms from the highest to the lowest contrast tested, and did not vary sgnificantly with eccentricity.
The multifocal visual evoked potential: An objective measure of visual fields?
Vision Research, 2005
We examined the effects of inter-modal attention and mental arithmetic on Humphrey visual field sensitivity and multifocal visual evoked potential (mfVEP) amplitude. Four normally sighted subjects (ages ranging from 24 to 58 years) participated in this study. Monocular visual field sensitiv ity was measured under two conditions: (1) standard testing condition and (2) while the subject performed a Paced Auditory Serial Addition Task (PASAT). Monocular mfVEPs were recorded in response to a 60-sector stimulus. The checkerboard pattern in each sector was contrast reversed according to a binary m-sequence. mfVEPs were recorded under two conditions: (1) standard testing conditions and (2) while the subject performed a PASAT. We found that, when compared to the notask condition, all subjects had locations of significantly reduced Humphrey visual field sensitivities when performing the PASAT. In contrast, there were no significant decreases in mfVEP amplitude in any sector for any of the subjects while performing the PASAT. Our findings indicate that divided attention and ongoing mental processes did not affect the mfVEP. Therefore, the mfVEP provides an objective measure of visual field function that may be useful for some patients with unreliable automated static perimetry results.
The topography of visual evoked response properties across the visual field
Electroencephalography and Clinical Neurophysiology, 1994
Visual evoked potentials (VEPs) to luminance and pattern reversal stimulation were derived for a large number of small areas throughout the central visual field. In one study, the field was tested with a stimulus array consisting of 64 equal-area patches. Local response components were extracted by independent m-sequence modulation of the patches. Field topographies were compared between and within subjects using different electrode placements. The subject-dependent local variability observed in response characteristics is attributed to contributions from two or more cortical representations of the visual field and to inter-subject variations in gross cortical anatomy. The second study used luminance modulation of 56 patches across a 15 ° field, scaled to activate approximately equal cortical areas in area V1. This produced many robust signals at all eccentricities. Bipolar and double differential ("l-dimensional Laplacian") signals were compared. The double differencing reduced contributions from distant or distributed sources, enhancing nearby current source activity, and greatly improved S/N for many stimulus locations. The high-resolution visual field maps demonstrated that clinical field testing using the VEP is not feasible because of effects of cortical convolutions on responses. However, the vast improvement in data quality and quantity make it a useful tool for VEP source localization and identification.
International Journal of Psychophysiology, 1994
Visual evoked magnetic responses to pattern onset/offset stimuli were recorded in 5 normal subjects. The outgoing and ingoing magnetic currents were seen maximally over the contralatcral visual cortex to the half field stimulated in the majority of subjects. The distribution of magnetic currents with half field stimulation would be consistent with a dipole on the midline with the positive end pointing laterally. Quadrantic stimuli produced dipoles which would be consistent with a vector sum of dipoles situated, in the case of upper quarter field stimulation, in the lingual gyri on the floor of the calcarine fissure. Lower quadrantic stimulation produced a vector consistent with dipoles on the cuneal gyrus and on the ceiling of the calcarine fissure producing a resultant vector. The use of paired o&ant stimuli to improve localisation was demonstrated on both right left and upper and lower half fields.
Japanese Journal of Ophthalmology, 2011
Purpose To introduce a method for improvement of multifocal VEP (mfVEP) recordings by prediction of waveforms at multiple positions on the surface of the skull. Methods Fifteen healthy participants (mean age 24 ± 3.8 years) underwent mfVEP recordings from 3 surface positions. Two methods of a best-of-mfVEP approach were used and compared. In the first, a standard procedure, further data from 3 calculated channels were used. In the second approach, mfVEPs were obtained by using data derived from 40 virtual electrode positions on the basis of predictions from dipole source calculations. Results The mean signal-to-noise ratios (SNRs) of the best-of-mfVEPs of both methods were compared. The SNR was significantly higher for mfVEP data using additional virtual recordings revealed by dipole source determination (2.87 vs. 3.36; P \ 0.035). Conclusion We conclude that multichannel prediction of mfVEP responses based on dipole source calculation significantly improves the quality of the examination results compared with the currently prevalent standard method.
The Pattern-Pulse Multifocal Visual Evoked Potential
To define the pattern-pulse multifocal visual evoked potential (PPMVEP) and determine its characteristics in a sample of normal subjects in terms of amplitude of response attainable, the variation in waveform across visual field, and distribution of potential over the scalp and to compare patternpulse with contrast-reversal multifocal stimuli. METHODS. VEPs were obtained by concurrently stimulating 60 regions of a cortically scaled dartboard with pulses of pattern contrast. Responses were recorded from normal subjects, by using a 32-channel electroencephalogram recording system, and elementary responses to each region were estimated by multiple regression of each of the response channel signals on stimulus signals. Left-eye, right-eye, and binocular viewing conditions were concurrently tested by dichoptic stimulation. A direct comparison was then made with contrast-reversal stimulation. RESULTS. Response waveform sets for 12 subjects varied in maximum amplitude from 1.8 to 6.8 V. A stereotypical distribution of waveforms held in most subjects, depending primarily on the polar angle location of the stimulus within the visual field. In a direct comparison with a contrast-reversal multifocal analysis, the pattern-pulse responses had similar waveforms and scalp topography, but were 15 times larger in amplitude. Root mean square (RMS) signal-to-noise ratio (SNR) was 1.9 times higher with pattern-pulse stimulation, corresponding to a reduction of 73% in recording time to achieve the same SNR. CONCLUSIONS. The PPMVEP can simultaneously characterize 60 regions of the visual field for both eyes in less than 7 minutes. A general methodology is illustrated that allows multifocal analysis with flexible choice of stimulus conditions. (Invest Ophthalmol Vis Sci. 2003;44:879 -890)
Effect of different stimulus configurations on the visual evoked potential (VEP)
Documenta Ophthalmologica, 2012
The purpose of this study was to assess changes in the response profile of the pattern visual evoked potential (VEP) using three stimulus configurations simulating visual-field scotomas: central circular and central blank fields increasing incrementally in diameter from 1°to 15°, hemi-field, and quadrant patterns. Five visually normal adult subjects (ages 22-68 years) were tested binocularly at 1 m for each stimulus configuration on 5 separate days. A checkerboard test pattern (64 9 64 black-and-white checks, 85 % contrast, 64 cd/m 2 luminance, 20 s of stimulus duration, 2-Hz temporal frequency) was used. The group mean VEP amplitude increased in a linear manner with increase in the central circular diameter (y = 0.805x ? 2.00; r = 0.986) and decrease in central blank field diameter (y =-0.769x ? 16.22; r = 0.987). There was no significant change in latency in nearly all cases. The group mean coefficient of variability results indicated that the VEP amplitude was repeatable for the different stimulus configurations. The finding of VEP response linearity for the circular stimulus fields, and repeatability for all stimulus configurations, suggests that the clinician may be able to use the VEP technique with the suggested test patterns as a rapid and simple tool for objective assessment for several types of visual-field defects for a range of abnormal visual conditions and special populations.