Types Of Visual Evoked Potentials Research Articles

Analysis of Visual-Evoked Potentials of Primary Visual Cortex under Flash Stimulations

Visual-evoked potentials (VEPs) which is made up of electrical signals generated by the nervous system in response to a stimulus can be easily recorded from the visual cortex of the experiment animal. There are several types of VEPs, for example, flash evoked potential (FEP), pattern evoked potential [1-3]. The FEP is produced by a visual stimulation with a brief and diffuse flash light. It is frequently used to evaluate the neural activity and sensory processing in the visual system [ and to identify and characterize the changes occurring in the retina and the occipital cortex [4, 5]. VEPs can also provide a further therapeutic approach through the stimulate of monitoring neurophysiologic changes related to diseases [6, 7]. The pattern evoked potentials have been used to assess parametric characteristics of visual perception, detect neuronal irritability and diagnose neurological diseases [8-1.

Evidence for rapid face recognition from human scalp and intracranial electrodes

It is still generally believed that complex visual analysis is not carried out within the first 100 ms. Here we show that intra- and extracranial visual evoked potentials (VEPs) differentiate previously seen faces from novel faces as early as 50 ms after stimulus onset. EEG was recorded from scalp electrodes in 12 male healthy volunteers (group I) and intracranially from implanted depth electrodes in the temporal and frontal cortex of seven epilepsy patients (group II). Both groups were engaged in a face recognition task. All subjects showed significant differential responses which occurred very early (50-90 ms) and later (190-600 ms). In group II, the early responses were recorded more frequently in the right hemisphere, whereas the late differential VEPs were found in both hemispheres. Both types of VEPs were more frequent in the temporal neocortex, underlining its role as a major contributor to these fast recognition processes.

Visual Evoked Potentials in Early Alzheimer's Dementia: An Exploratory Study

Topographical maps of visual evoked potentials (VEPs) were recorded from 10 possible Alzheimer's disease (AD) patients and 10 control subjects. The purpose of the study was to determine if the two types of VEPs could function as a diagnostic screening for AD. Results of the statistical analysis did not reveal any latency differences between VEPs for the components elicited by either the pattern shift visual evoked potential (PSVEP)--or flash visual evoked potential (FVEP)--elicited components for AD patients compared with the control subjects; however, the information provided insight into results that are frequently lost with conventional evoked potential data. Statistically significant differences in amplitude were found between the P1 and the N2 of the PSVEP at 124, 126, and 130 ms, and at 116 ms for the FVEP.

Electro-physiological investigation of edge-selective mechanisms of human vision

This study investigates the spatial and temporal characteristics of human visual mechanisms that respond selectively to the polarity of edges. The technique was to record steady-state visual evoked-potentials (VEPs) while visually stimulating with a sawtooth waveform (a series of edges of the same polarity) periodically reversing in contrast (and hence edge-polarity) at a suitable frequency. To ensure that phase-locked VEPs resulted from polarity reversal (rather than local luminance modulation) the stimuli were randomly jittered to a new position between each contrast reversal. The jittered stimulus elicited strong and reliable second-harmonic modulation, usually about one-fifth the amplitude of standard VEPs under similar conditions. The amplitude and extrapolated thresholds of polarity-specific VEPs (relative to standard VEPs) did not vary with eccentricity (up to 10°) or with stimulus orientation. The dependency on spatial frequency was similar to that of standard VEPs, but the polarity-specific VEPs tended to peak at lower temporal frequencies. Perhaps the clearest difference in the two types of VEPs was in the estimated response latency, about 140msec for the polarity VEPs, compared with 90msec for standard VEPs.