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At least 919 records · Page 51Linked to original sources
PubMed1986

Visual evoked response in head trauma: pattern-shift stimulus.

Studies of visual evoked potentials in head injuries have all utilized the flash stimulus. We studied the efficacy of monocular pattern-shift visual evoked potentials (PSVEPs) in eliciting residual dysfunction of the visual pathways in 33 patients 6 to 24 months after head injury. Those with ocular trauma or ocular pathology were not included. Abnormal PSVEPs were seen in one-third of 33 head-injured patients. Only 1 (11%) of 9 patients with mild cognitive impairment had abnormal PSVEPs compared with 7 (39%) of 18 with moderate and 3 (50%) of 6 with severe cognitive impairment.

Adolescent↗
PubMed1997

Striate cortical generators of the N75, P100 and N145 components localized by pattern reversal visual evoked magnetic fields.

Magnetic fields evoked by checkerboard pattern reversal visual stimulation to the monocular left or right half-field were recorded over the whole head using a helmet-shaped 64 channel magnetoencephalography system in fourteen normal subjects. The sources of the triphasic N75m-P100m-N145m responses were located using a single current dipole model. Relative locations and orientations of the N75m and N145m dipoles to the P100m dipole were calculated for each subject to reduce errors due to 'anatomical variability and then averaged for all subjects under the same stimulus conditions. These averaged parameters showed that N75m and N145m originated from the same location in the striate cortex as P100m and reversed their orientations successively by 180 degrees during the time course.

Adult↗
PubMed1996

Spatial frequency-dependent asymmetry of visual evoked potential amplitudes.

The extent to which pattern reversal evoked potential amplitudes are distributed symmetrically over the scalp was investigated as a function of stimulus spatial frequency. Nine right-handed male subjects viewed sinusoidal grating stimuli of 4.0 and 0.5 c/deg phase reversed every 900 msec. A visual half-field configuration enabled selective stimulation of the right- or left-hemisphere visual cortex. Evoked responses were recorded from the 2 cm above the inion (Oz) and at 7 and 13 cm lateral to Oz. Analyses of normalized evoked response amplitudes showed a significant asymmetry for the 4.0 c/deg stimulus; right-hemisphere amplitudes declined as a function of distance from the midline, while left-hemisphere amplitudes were greatest at the 7 cm recording site. No hemispheric differences were observed for the 0.5 c/deg stimulus; amplitudes for both hemispheres declined as a function of distance from the midline. The data are discussed in terms of hemispheric differences in morphology and functional asymmetries at early levels of sensory processing.

Adolescent↗
PubMed1988

The pattern flash elicited P300-complex (PF-P300): a new method for studying cognitive processes of the brain.

For neurological purposes we developed a new method for eliciting P300-waves: Using two different kinds of checkerboard stimuli that were randomly flashed on a TV screen we obtained, besides the well-known usable primary complex, prominent PF-P300-complexes consisting of a marked negative potential (= N250), the PFP300a and the N400 peaks. These components could be related to different cognitive processes such as floating versus selective sustained attention and stimulus evaluation. N250 especially was shown to be closely related to different degrees of difficulty in visual discrimination. Further, the PFP300 components are test-retest reliable and sex-independent. Since they have relative small interindividual variabilities, we consider the N250- and PFP300a-latencies especially as well as the ascending PFP300a-amplitudes to be appropriate parameters for investigating diseases with cognitive disorders objectively.

Brain↗
PubMed2000

An electrophysiological index of stimulus unfamiliarity.

This study investigated the functional significance of the N2 response to novel stimuli. In one condition, background, target, and deviant stimuli were simple geometric figures. In a second condition, all stimulus types were unfamiliar/unusual figures. In a third condition, background and target stimuli were unusual figures and deviant stimuli were simple shapes. Unusual figures, whether they were deviant, target, or background stimuli, evoked larger N2 responses than their simple, familiar counterparts. N2 elicited by an unusual background stimulus was larger than that evoked by simple, deviant stimuli, a pattern opposite that exhibited by the subsequent P3. Deviance from immediate context had limited influence over N2 amplitude. The results suggest that novelty N2 and novelty P3 reflect the processing of different aspects of "novel" visual stimuli. The novelty P3 is particularly sensitive to deviation from immediate context. In contrast, the novelty N2 is sensitive to deviation from long-term context that renders a stimulus unfamiliar and difficult to encode.

Adult↗
PubMed2001

Electroencephalogram-based scaling of multifocal visual evoked potentials: effect on intersubject amplitude variability.

PURPOSE: The interindividual variability of the visual evoked potential (VEP) has been recognized as a problem for interpretation of clinical results. This study examines whether VEP variability can be reduced by scaling responses according to underlying electroencephalogram (EEG) activity. METHODS: A multifocal objective perimeter provided different random check patterns to each of 58 points extending out to 32 degrees nasally. A multichannel VEP was recorded (bipolar occipital cross electrodes, 7 min/eye). One hundred normal subjects (age 58.9 +/- 10.7 years) were tested. The amplitude and inter-eye asymmetry coefficient for each point of the field was calculated. VEP signals were then normalized according to underlying EEG activity recorded using Fourier transform to quantify EEG levels. High alpha-rhythm and electrocardiogram contamination were removed before scaling. RESULTS: High intersubject variability was present in the multifocal VEP, with amplitude in women on average 33% larger than in men. The variability for all left eyes was 42.2% +/- 3.9%, for right eyes 41.7% +/- 4.4% (coefficient of variability [CV]). There was a strong correlation between EEG activity and the amplitude of the VEP (left eye, r = 0.83; P < 0.001; right eye, r = 0.82; P < 0.001). When this was used to normalize VEP results, the CVs dropped to 24.6% +/- 3.1% (P < 0.0001) and 24.0% +/- 3.2% (P < 0.0001), respectively. The gender difference was effectively removed. CONCLUSIONS: Using underlying EEG amplitudes to normalize an individual's VEP substantially reduces intersubject variability, including differences between men and women. This renders the use of a normal database more reliable when applying the multifocal VEP in the clinical detection of visual field changes.

Adult↗
PubMed2002

[Visual perception of Kanji characters and complicated figures. II. Visual P300 event-related potentials in patients with mental retardation].

In order to objectively evaluate visual perception of patients with mental retardation (MR), the P300 event-related potentials (ERPs) for visual oddball tasks were recorded in 26 patients and 13 age-matched healthy volunteers. The latency and amplitude of visual P300 in response to the Japanese ideogram stimuli (a pair of familiar Kanji characters or unfamiliar Kanji characters) and a pair of meaningless complicated figures were measured. In almost all MR patients visual P300 was observed, however, the peak latency was significantly prolonged compared to control subjects. There was no significant difference of P300 latency among the three tasks. The distribution pattern of P300 in MR patients was different from that in the controls and the amplitudes in the frontal region was larger in MR patients. The latency decreased with age even in both groups. The developmental change of P300 latency corresponded to developmental age rather than the chronological age. These findings suggest that MR patients have impairment in processing of visual perception. Assessment of P300 latencies to the visual stimuli may be useful as an objective indicator of mental deficit.

Adolescent↗
PubMed1998

[The significance of combination of electrophysiology and automated perimetry tests on the early diagnosis of primary open angle glaucoma].

OBJECTIVE: The study was designed to analyze the relationship among the three electrophysiological tests and visual fields in primary open angle glaucoma (POAG) in order to find some more sensitive and specific parameters in earlier and early diagnosis of patients with POAG. METHODS: Thirty-six(70 eyes) patients with POAG, 8(12 eyes) glaucoma suspects and 30 (60 eyes) normal subjects underwent pattern electroretinogram (PERG), oscillatory potentials (OPs), pattern visual evoked potentials (PVEP) and Humphery automated perimetry tests respectively. RESULTS: The abnormal rate of PERG was the highest among the three electrophysiological tests in the glaucoma suspects and those of PERG and automated perimetry results were higher than others after early stage. In the correlation analysis of all objects, the amplitude of PERG had negative correlated with IOP and visual indices, but no correlation with C/D and VA. OPs had negative correlated with C/D, and no correlation with visual fields indices, intraocular pressure (IOP) and visual acuity (VA). The latency of PVEP had positive correlation with visual fields indices and C/D, but no correlation with IOP. CONCLUSION: Statistical result showed that different parameters could be selected according to different appearance of POAG. In the earlier stage before visual field defects could be found, PERG would be a more sensitive indicator if IOP were high; once C/D was abnormal, OPs and PVEP would be the better signs even though IOP was normal. PERG and Humphery automated perimetry were very useful indicators after early stage. It was significant in combination of many visual function tests on earlier or early diagnosis of POAG.

Electrophysiology↗
PubMed1992

Effect of attention on the VEP in binocular and monocular conditions.

To study the effect of voluntary concentration on the visual evoked potential (VEP) with monocular and binocular rivalry stimulation, pattern reversal VEPs were recorded using 5.5 min arc and 50 min arc check sizes. Subjects viewed the VEP stimulus with the left eye and a light emitting diode (LED) with the right eye. They were asked to concentrate on either the VEP stimulus or the LED. The two targets were arranged so that the left eye remained accurately focused on, and directed to, the centre of the VEP stimulus throughout the recordings. The binocular VEP wave became attenuated when the subject concentrated on the LED. The wave was reduced to around two-thirds of the amplitude present when concentrating on the VEP stimulus. This reduction in the VEP amplitude is considered to be due to a binocular interaction because there was a lack of amplitude attenuation when the experiment was repeated with monocular conditions. The results also suggest that the wave is smaller when the non-dominant eye receives the VEP stimulus compared with that when the dominant eye is stimulated by the VEP target.

Adolescent↗
PubMedDate not supplied

Reliability and upper normal variability limits of pattern reversal visual evoked potential parameters.

Twenty healthy volunteers aged 21-48 years (10 males, 10 females) were submitted to pattern reversal visual evoked potentials with 15' and 30' checks. The recordings were repeated after 7 days to assess reliability and upper normal variability limits of the following parameters: latencies of N70, P100, N140 and peak-to peak amplitudes of N70-P100, P100-N140. Reliability was tested with intraclass correlation coefficient, which was excellent or good for all parameters. Test-retest variability limits were computed with = 0.01 for absolute latency differences and relative amplitude differences.

Adult↗
PubMed2003

[Evaluation of EEG(D2) and CNV correlation dimension in various forms of visual attention in human].

In 16 healthy subjects, the EEG and the CNV (contingent negative variation) correlation dimension was studied during preparing to pay attention to one of three attention tasks: the situations "What", "Where" and "What and where". Two easily discernible symbols (squares and circles) were used as stimuli. The findings show that, irrespective of the attention form, the correlation dimension of the EEG, the CNV amplitude, and the evoked potential's N1-P3 component amplitude had maximal values in the temporal leads. The temporal visual system seems to play a domineering part in the tasks of spatial and non-spatial attention to stimuli in humans.

Adolescent↗
PubMed2005

Visual evoked potentials and event related potentials in congenitally deaf subjects.

The purpose was to test parameters of visual evoked potentials (VEPs) and of event-related potentials (ERPs) in deaf subjects to verify visual and cognitive CNS functions in a handicapped group of the population. Three types of visual stimuli (with dominating parvocellular or magnocellular system activation or with cognitive tasks) were used in the study. Six deaf persons (4 women, 2 men, mean age 17 years) and 6 persons with normal hearing (sex- and age-matched) were included in this pilot study. In all types of stimulation, latencies and amplitudes of main VEPs and ERPs components were evaluated. No significant latency differences were found. However, significantly reduced amplitudes were found in the occipital area for responses to motion and cognitive stimuli which might be interpreted as a part of functional reorganization of the extrastriate and cognitive cortical areas of deaf subjects.

Adolescent↗
PubMed2004

[An event-related potential study the on information processing of binocular disparity in random-dot stereogram].

OBJECTIVE: To study the effects of discontinuous-continuous disparity gradient, uncrossed-crossed disparity and small-large disparity in random-dot stereogram (RDS) on the event-related potentials (ERPs). METHOD: Behavioral data and ERP were recorded when 16 healthy participants (8 males and 8 females) with normal depth perception were performing the task, in which the stereopsis were generated by red-blue glasses. RESULT: 1) The accuracy in discontinuous disparity gradient was higher than that in continuous disparity gradient, and the accuracy in large disparity was higher than that in small one. 2) Discontinuous disparity gradient elicited shorter N160 latency and larger N350 amplitude than continuous disparity gradient did. Compared with uncrossed disparity, crossed disparity elicited shorter N350 latency. In addition, large disparity elicited shorter N160 latency and larger P280 amplitude than small disparity did. CONCLUSION: The effect of disparity gradient on disparity information processing is significant, and the discontinuous disparity gradient has its processing advantage. Latency of N160 and amplitude of P280 is correlated with the information processing of the size of disparity. N350 component is correlated with the information processing of the uncrossed-crossed information of disparity.

Adult↗
PubMed1992

Apparent accommodation in pseudophakic eyes as measured with visually evoked potentials.

We measured apparent accommodation with pattern reversal visually evoked cortical potentials in 27 pseudophakic eyes after the implantation of posterior chamber intraocular lenses. The patients ranged in age from 47-83 years. The amplitude of accommodation was not significantly different between pseudophakic eyes and normal phakic eyes. Apparent accommodation was inversely proportional to the pupillary diameter and was significantly correlated with corneal astigmatism. No significant relationship was noted between apparent accommodation and age of patients, corrected visual acuity, or refractive error.

Accommodation, Ocular↗