Identification of the stimulated hemiretinae using a reduced number of PVEP trials (original) (raw)
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Electroencephalography and clinical neurophysiology, 1996
Lateral hemifield pattern-reversal visual evoked potential (PVEP) field data were evaluated using potential distributions, dipole modelling and distributions of Hilbert transformation-based instantaneous frequency in order to determine the stimulated hemisphere. Twenty channel records were collected from 35 normal volunteers in two laboratories using similar stimulus conditions (11-20.5 degrees target, 60-75 min checks, 2/s reversal, 500 ms analysis epoch). P100 latency was determined in each average by the global field power maximum between 90 and 120 ms. Using the data from O1 and O2 at P100 latency, the stimulated hemisphere was identified by maximal potential or minimal instantaneous frequency on the stimulus-contralateral side, or, using the 20-electrodes data at P100 by the ipsilateral lateralization of the dipole model. Correct classification of the stimulated 70 hemiretinae was achieved by potential distribution in 44 cases, by dipole modelling in 54 cases and by instantaneo...
Spectral Analysis of the Visual Evoked Potential (VEP): Effects of Stimulus Luminance
Psychophysiology, 1984
Power spectral analysis was performed on the visual evoked potentials (VEPs) of subjects who had participated in an augmenting-reducing study. Six flash luminances were used (0.31, 0.65,1.25, 2.5, 5.0, and 10.0 fL). EEG recordings were taken from £" O,, Oj, Tj, and T4 scalp locations. Power in six frequency ranges was examined (0-2, 2-6, 6-10,10-14,14-18, and 18-22 Hz). Power in the lowest three frequency ranges increased linearly with stimulus luminance at all electrode sites. Power in the highest three ranges increased linearly with luminance at occipital sites only. Power was greater in the left hemisphere than in the right for 18-22 Hz activity recorded at occipital locations. The reverse asymmetry occurred for 6-14 Hz activity recorded at temporal locations. The results suggest that individual differences in stimulus control in EEG recordings taken from scalp locations overlying nonspecific cortex are due primarily to the contributions of higher frequency components of the VEP spectrum. A thalamo-cortical model of stimulus control is described.
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.
A Comprehensive Review on Methodologies Employed for Visual Evoked Potentials
Scientifica, 2016
Visual information is fundamental to how we appreciate our environment and interact with others. The visual evoked potential (VEP) is among those evoked potentials that are the bioelectric signals generated in the striate and extrastriate cortex when the retina is stimulated with light which can be recorded from the scalp electrodes. In the current paper, we provide an overview of the various modalities, techniques, and methodologies which have been employed for visual evoked potentials over the years. In the first part of the paper, we cast a cursory glance on the historical aspect of evoked potentials. Then the growing clinical significance and advantages of VEPs in clinical disorders have been briefly described, followed by the discussion on the earlier and currently available methods for VEPs based on the studies in the past and recent times. Next, we mention the standards and protocols laid down by the authorized agencies. We then summarize the recently developed techniques for...
Low-contrast Pattern-reversal Visual Evoked Potential in Different Spatial Frequencies
Journal of Ophthalmic and Vision Research, 2020
Purpose: To evaluate the pattern-reversal visual evoked potential (PRVEP) in lowcontrast, spatial frequencies in time, frequency, and time-frequency domains. Methods: PRVEP was performed in 31 normal eyes, according to the International Society of Electrophysiology of Vision (ISCEV) protocol. Test stimuli had checkerboard of 5% contrast with spatial frequencies of 1, 2, and 4 cycles per degree (cpd). For each VEP waveform, the time domain (TD) analysis, Fast Fourier Transform(FFT), and discrete wavelet transform (DWT) were performed using MATLAB software. The VEP component changes as a function of spatial frequency (SF) were compared among time, frequency, and time–frequency dimensions. Results: As a consequence of increased SF, a significant attenuation of the P100 amplitude and prolongation of P100 latency were seen, while there was no significant difference in frequency components. In the wavelet domain, an increase in SF at a contrast level of 5% enhanced DWT coefficients. Howev...