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PubMed1987

Involvement of somatosensory and visual pathways in late onset ataxia.

Nerve conduction studies, median nerve somatosensory (SEPs) and pattern-reversal visual evoked potentials (VEPs) were recorded in 10 patients with late onset ataxia. Nine patients had dysfunction of somatosensory pathways, eight of them axonal polyneuropathy in nerve conduction measurements, and four had also impaired impulse conduction along the visual pathways. Abnormalities in records of evoked potentials occurred as prolonged latencies rather than reduced amplitudes. The observed dysfunction of peripheral and central pathways was not related to the duration or the severity of the clinical involvement by the disease. It is emphasized, however, that there seemed to be a relationship between the prolonged SEP latencies and the impaired peripheral nerve conduction values and between the diminished VEP amplitudes and the most delayed VEP latencies.

Adult↗

PubMed1987

Variability on serial testing of pattern reversal visual evoked potential latencies from full-field, half-field and foveal stimulation in control subjects.

The change in pattern reversal visual evoked potential (PRVEP) latency over time (test-retest variability, TRV) was assessed in 30 (16 males, 14 females) adult control subjects using full-field (FF), half-field (HF) and foveal (central-field, CF) stimulation. The mean test-retest interval (TRI) was 20.5 months with a range of 18-21.5 months. There were no significant test-retest latency differences in either sex and furthermore there were no significant inter-sex differences in any of the test-retest parameters. Because of the latter finding the test-retest upper limit of normal for each parameter as defined by the mean value + 2.5 S.D. was taken as the largest value obtained in either sex. Thus the test-retest upper limits of normal for absolute latency from FF, right HF, left HF and CF stimulation were 6, 7, 9 and 7 msec, respectively; for interocular latency differences (ILD) from FF and CF stimulation were 4 and 5 msec respectively; and for right HF to left HF intraocular latency difference (IOLD) was 7 msec. It is concluded that the TRV was sufficiently small in our control group with each of the stimulus techniques to make all of them potentially useful in serial PRVEP studies. Furthermore the extra information provided by CF and HF stimulation may increase the sensitivity and accuracy with which change can be monitored.

Adult↗

PubMed1989

Event-related potentials and the semantic matching of faces.

Event-related brain potentials (ERPs) were recorded while subjects determined whether two sequentially presented famous faces depicted individuals belonging to the same or to different occupational categories. During the 1.56 sec interval between the onset of the faces, ERPs recorded from right hemisphere electrodes were more negative-going than those from electrodes over the left hemisphere. The ERPs evoked by the second face on each trial differed as a consequence of whether or not the person depicted belonged to the occupational category specified by the first face. This difference took the form of a bilaterally-distributed negative-going shift in the ERPs evoked by non-matching as opposed to matching faces. This negativity was maximal around 450 msec post-stimulus. The ERP asymmetries during the inter-stimulus interval are interpreted as evidence for the engagement of cognitive processes lateralized to the right hemisphere. The match/non-match differences are considered to reflect the modulation of an "N400" component similar to that evoked by words, and thus suggest that such components can be modulated by associative priming between non-linguistic stimuli.

Adult↗

PubMed1992

Parallel and serial visual search after closed head injury: electrophysiological evidence for perceptual dysfunctions.

Event-related potentials (ERPs) were recorded from closed head injury (CHI) patients at least 2 years postinjury and from controls in order to assess their parallel and serial processing abilities during visual search. In Experiment 1, stimuli consisted of arrays of eight triangles; half of the arrays contained a target item. In the "feature-present" condition, the target item was a triangle with an additional horizontal line that could be detected automatically and in parallel, while in the "feature-absent" condition all items except for the target triangle had an additional horizontal line, thus requiring a serial search. In Experiment 2, stimuli consisted of eight solid bars (50%), seven solid bars and a vertical open bar (25%), and seven solid bars and a horizontal open bar (25%): the array containing the horizontal bar served as a target. By recording ERPs to the arrays containing vertical open bars, which were similar to the target items, parallel processing of "pop-out" stimuli could be studied in the absence of any overt response. ERP data were compared with the results of neuropsychological and neuroimaging (MRI, CAT) examination. Patient exhibited a decreased behavioral performance both in the parallel and in the serial processing mode. Furthermore, abnormalities of early and intermediate ERP components (P1, N1, P2, N2) were found, whereas the late component (P3) was less affected by CHI. The results were interpreted as an index of CHI-induced dysfunctions in perceptual processes such as simple feature registration and early target discrimination. It was suggested that these dysfunctions contribute to impairments of parallel as well as serial processes in visual search.

Adult↗

PubMed1984

The efficiency of the central and peripheral retina in driving human optokinetic nystagmus.

Previous experiments to decide whether the gain of optokinetic nystagmus (OKN) is increased or decreased by occlusion of the central retina involved the use of stationary edges on the occluder and unmatched contrasts. With these factors controlled, it was confirmed that OKN gain is severely reduced by occlusion of the central retina but only at stimulus velocities above about 30 degrees/sec. The gain of horizontal OKN was found not to increase with increasing width of the display if the lateral edges are blurred. The high gain of centrally driven OKN may be related to the ability of higher mammals to stabilize the images of objects at a given distance in a complex parallactic visual field.

Humans↗

PubMed1986

Temporal frequency-dependent VEP changes in Parkinson's disease.

We recorded steady-state (4.19 and 8.41 Hz) VEPs in 17 Parkinson's Disease (PD) patients and 18 control observers using on-off temporal modulation of a 2.3 c/deg sinusoidal grating. With 4.19 Hz, 20 out of 33 PD patient eyes had abnormal VEPs. However, only 8 of 33 eyes were abnormal with 8.41 Hz. "Routine" (counterphase) transient VEPs revealed delayed VEPs for only 7 out of 24 eyes of the patients. These findings suggest an "input" temporal frequency-dependent abnormality in the foveal pathway.

Adult↗

PubMed1986

The use of a system analysis approach to electrodiagnostic (ERG and VEP) assessment.

To evaluate the integrity of a biological system and its constituent functional units, a systematic study of input-output relations adopted from engineering has proven appropriate. With such an approach, sequential analysis can be implemented to probe the various parameter extractions along, for example, the visual system. The a priori assumption in this approach is that the visual world is processed along functionally separate pathways yielding distinct percepts such as contrast and motion. This so-called channel approach has proven useful not only to basic vision research but also for clinical application. The present overview shows that on the basis of the ERG or VEP, a type of functional anatomy can be performed with the biological system of interest remaining intact. Finally, it will be demonstrated that electrophysiological output parameters of the visual system can also serve as a non-invasive entry to investigate general systemic disorders.

Adult↗

PubMed1996

The role of high-order phase correlations in texture processing.

Isodipole textures are pairs of texture ensembles whose autocorrelations, and hence power spectra, are equal. Examples of readily discriminable isodipole textures are well known. Such discriminations appear to require feature extraction, since the isodipole condition eliminates ensemble differences in spatial frequency content. We studied the effects of phase decorrelation on VEP indices of discrimination of isodipole texture pairs. Phase decorrelation, which ranged from 0.125 pi radians (slight randomization) to pi radians (complete randomization), was introduced in two ways: by independent jittering of each spatial Fourier component, and by a product method, which preserved correlations among certain quadruples of spatial Fourier components, despite pairwise decorrelation. For the even/random isodipole texture pair, independent phase decorrelation greater than 0.5 pi radians markedly reduced VEP indices of texture discrimination for all check sizes, and eliminated them entirely for check sizes of 8 min or greater. However, the product method preserved texture discrimination signals even with complete pairwise randomization of spatial phases. For the triangle/random isodipole texture pair, both kinds of phase decorrelation eliminated VEP indices of texture discrimination. These results imply that isodipole texture discrimination is based on fundamentally local processing, and not on global Fourier amplitudes-since the phase manipulations which eliminate texture discrimination preserve the Fourier amplitudes. The dependence of the antisymmetric response component (the odd harmonics) on phase decorrelation and texture type is consistent with a previously proposed model for feature extraction, and leads to constraints on how texture processing is modulated by contrast. The limited contribution of global spectral characteristics for small checks is consistent with a previously identified breakdown in scale-invariant processing.

Adult↗

PubMed1989

Event-related potentials during word-reading and figure-matching in left-handed and right-handed males and females.

In two experiments, event-related potentials at left and right occipital, parietal, and temporal sites were studied in 16 left-handers (8 male, 8 female) and 16 right-handers (8 male, 8 female). Subjects displayed extreme handedness, had a normal writing hand position, reported no left-handed relatives, and reported no perinatal traumata. In Experiment 1, centrally presented words had to be read, and nonverbal stimuli had to be matched. Condition-dependent asymmetries were found for P340 and SW components. Word-reading elicited a N500 component, whereas figure-matching did not. In Experiment 2, words presented to either the left or right visual field had to be read. It was found that N160 measures were larger, and P240, P400, and SW measures were smaller to words presented in the contralateral visual field compared to words in the ipsilateral field. Sex affected these pathway effects. In both experiments, hand preference did not significantly influence the ERP results.

Adult↗

PubMedDate not supplied

The pattern electroretinogram: N95 amplitudes in normal subjects and optic neuritis patients.

Recent work has suggested that the N95 peak of the transient pattern electroretinogram (PERG) may be a more sensitive indicator of the late stages of retinal function prior to optic nerve activation than the P50 peak. In this report, we show that a new measure of N95 amplitude, based on digital filtering methods to identify a non-linear baseline before measurement, greatly reduced the amplitude variation in a population of 50 normal subjects when compared with two other plausible measures. We then used that new measure to follow the time course of N95 amplitudes in 12 optic neuritis patients. It was found that maintenance of a normal N95 amplitude at 6 months after onset of optic neuritis was always associated with excellent clinical recovery as measured by visual fields, acuity, presence or absence of an afferent pupil and optic atrophy, and contrast sensitivity (CS). Loss of N95 amplitude to below laboratory limits of normal was associated with abnormalities in these indicators of visual function. This study supports the idea that the N95 peak represents retinal ganglion cell function.

Adolescent↗

PubMed1994

Use of pattern electroretinography to differentiate acute optic neuritis from acute anterior ischemic optic neuropathy.

The transient pattern electroretinogram (PERG) was recorded from 16 patients with acute optic neuritis and from 13 patients with acute non-arteritic anterior ischemic optic neuropathy (AION). All patients were tested within 35 days from the the onset of visual symptoms and all had significant central visual field abnormalities in their affected eyes as quantified by automated perimetry. Analysis of the PERGs showed that the amplitude of the N95 peak was abnormally reduced for each eye affected with AION while it remained normal in optic neuritis. No significant alteration in P50 amplitude was observed in either condition. The loss of N95 amplitude in AION was highly correlated with the average depth of visual field loss (in decibels) within a radius of 10 degrees of fixation. These results suggest that PERG could be used early in the course of optic neuropathy to distinguish optic neuritis from AION in those cases for which the diagnosis is still uncertain after the clinical examination.

Adult↗

PubMed1989

Mental rotation: an event-related potential study with a validated mental rotation task.

Event-related potentials (ERPs) were recorded while subjects performed a validated mental rotation task, taken from the cognitive psychology literature. These ERPs show a late posterior negativity relative to a baseline condition requiring all of the same perceptual and cognitive processes except for the mental rotation itself. Our tentative identification of this posterior negativity with mental rotation is further supported by the finding that it varies systematically with the amount of mental rotation required on a trial by trial basis in the experimental task. We conclude that this late negativity is an ERP marker of the mental rotation process, and that this process engages primarily posterior brain regions.

Arousal↗

PubMed1990

Handedness and hemispheric asymmetry of pattern reversal visual-evoked potentials.

Pattern reversal visual-evoked potentials (EP) from temporal leads in the two hemispheres of 26 right-handed (14 right-eye-dominant and 12 left-eye-dominant) and 10 left-handed (left-eye-dominant) adults were recorded. Checkerboard patterns (check sizes: 5.7 and 17 min of arc) at 1 and 8 Hz were reversed. Stimuli (a) subtended 6 degrees of visual field, (b) subtended 1 degree of visual field (foveal condition), and (c) were restricted to the annular portion of the visual field around the fovea (peripheral condition). Larger EP amplitudes in right or left hemisphere in relation to handedness, temporal frequency, and visual field condition were recorded. Eye dominance of dextrals appeared to play a role in determining the hemispheric asymmetry. Previous literature data and present results in relation to the hypothesis of different hemispheric specialization for basic visual information are discussed.

Adult↗

PubMed1993

Flash and pattern reversal visual evoked potentials in C57BL/6J and B6CBAF1/J mice.

Visual system responses (visual evoked potentials) to flash (FVEP) and pattern reversal (PRVEP) stimuli were recorded in mice. Two strains were used: black C57BL/6J mice and agouti B6CBAF1/J mice (first generation offspring of C57BL/6J females and CBA/J males.) Subjects were sedated with ketamine and xylazine. Flash rate (FVEP) and stimulus spatial frequency and pattern reversal rate (PRVEP) were varied to determine optimum stimulus parameters. Normative FVEP and PRVEP data were collected from mice of both strains after determination of optimum parameters. Five positive and four negative alternating peaks were routinely observed in the FVEP, while three positive and three negative alternating peaks were seen with the PRVEP. Varying the flash rate, the pattern reversal rate, and spatial frequency significantly affected nearly all amplitude and latency measures in the responses. Significant differences between strains were seen on some, but not all, latency and amplitude measures when the stimulus parameters were varied.

Animals↗

PubMed1996

Pattern shift visual evoked potentials in abstinent cocaine-dependent, alcohol-dependent, and cross-dependent patients.

The present study evaluated pattern shift visual evoked potential (VEP) amplitudes and latencies in four groups of adult subjects, characterized by the presence/absence of a recent history of alcohol dependence factorially crossed with the presence/absence of a recent history of cocaine dependence. All of the subjects were healthy and uncomplicated by histories of serious head injury, seizures (including drug-related seizures), and major medical, neurological, or psychiatric disorders. The subjects comprising the three patient groups were evaluated after 1 - 5 months of verified abstinence. Analyses of VEPs evoked by checkerboard reversal indicated a main effect of previous cocaine dependence on P100 latency. No main effect of previous alcohol dependence and no alcohol by cocaine dependence interaction were detected. The increased P100 latencies detected in abstinent, cocaine-dependent subjects are most likely related to cerebrovascular and neurological effects of chronic cocaine use.

Adult↗

PubMed2006

Neural correlates of shape-from-shading.

Visual evoked potentials were recorded during presentation of a single stimulus that generated bi-stable perceptual alternation between two different three-dimensional percepts. One interpretation (asymmetric) changed depth structure from flat to corrugated in depth and the other (symmetric) had the appearance of a flat surface translating laterally behind a set of apertures. Responses during perception of the asymmetric three-dimensional structure contained larger negative components than did responses during perception of the symmetric three-dimensional structure. Control experiments suggest that the interpretation of depth structure is selected after junction information caused by the interplay between shading and object shape is extracted.

Adult↗

PubMed2000

Effects of check size on pattern reversal visual evoked magnetic field and potential.

The effects of different check sizes on the 100m component of pattern reversal visual evoked magnetic fields (VEF) and the P100 component of visual evoked potentials (VEP) in terms of latency, amplitude and source localization were analyzed. Half field stimuli with or without central occlusion with check sizes of 15', 30', 60', 90' and 180' of visual arc were given to 7 healthy subjects. VEF and VEP were recorded simultaneously. The effect of the check size on the peak latency of both 100m and P100 was significant (P<0.01, ANOVA). The latencies for the smaller checks were significantly longer than those for the larger checks. The effect of the check size on the amplitude of the 100m to the stimulation with central occlusion was significant (P<0.05, ANOVA), but was not to the stimulation without central occlusion. That is, the amplitudes for the smaller checks were significantly smaller than those for the larger checks when using the stimulation with central occlusion, but not the stimulation without central occlusion. The effect of the check size on the P100 amplitude was not significant to the stimulation with and without central occlusion. The equivalent current dipoles were located around the calcarine fissure and did not differ significantly in location with check size. In conclusion, check size significantly affects the latency and amplitude of the 100m and/or P100, but not the receptive areas for the stimulation.

Adult↗

PubMed2003

Subjective contours and binocular rivalry suppression.

Binocular rivalry probably involves distributed neural processes, some responsible for dominance, others for suppression and still others for fluctuations in perception. Focusing on the suppression process, the present study asks whether neural events underlying rivalry suppression take place prior to, or subsequent to those underlying the synthesis of subjective contours. Specifically, we examined whether (i) a subjective contour could prematurely return a suppressed target to dominance and (ii) whether suppression of a Kanizsa-type inducer precludes the formation of a subjective contour. Suppression durations were not abbreviated by the subjective contour, but suppression did prevent the formation of a subjective contour. Evidently suppression precedes the synthesis of subjective contours in the visual processing hierarchy.

Adult↗