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PubMed2004

Binocular summation in visual evoked cortical potential in patients who have significantly different P100 peak latencies in their two eyes.

PURPOSE: To determine whether binocular summation in visual evoked cortical potential (VEP) is present in patients who have significantly different P100 peak latencies in their two eyes. METHODS: Twelve patients with unilateral optic neuritis (ON) and 11 normal controls were studied. All of them had visual acuity of > or = 20/20 in both two eyes and good stereoacuity. Transient and steady-state VEPs were recorded with monocular and binocular pattern-reversal stimulation. RESULTS: In normal controls, the binocular summation ratio was 1.05 with transient stimulation and 1.21 with steady-state stimulation, and in ON patients it was 1.19 and 1.30, respectively. In ON patients, the peak latency of P100 components was delayed significantly when the affected eye was stimulated, but with binocular stimulation the waveform was very similar to that when the fellow eye was stimulated. CONCLUSION: Binocular summation of VECP is not present in ON cases with large differences in the peak latency between the two eyes even if they have good stereoacuity. Binocular summation may not be correlated with stereopsis in adults whose binocular function has already matured.

Adolescent↗
PubMed2006

Simulation studies of the role of intracortical inhibition in the formation of sensitivity to cross-shaped figures.

The receptive fields of detector neurons for cross-shaped figures in the visual cortex were modeled in conditions of blockade of intracortical inhibition. The tuning of simulated neurons was compared with and without inhibition in the receptive field. In a simulated detector with convergence from two orientation detectors, acute tuning to the cross widened in the absence of inhibition, becoming invariant to the shape and orientation of the cross. A detector based on the disinhibition mechanism lost cross sensitivity when inhibition was blocked and became a detector for the orientation of a single bar. A model of a receptive field in which the inhibitory zones mask the tuning to a cross-shaped figure and in which blockade of inhibition affects only sensitivity is also proposed. We identified which of the properties of receptive field (configuration, location, zone weightings) allow them to simulate the properties of cat visual cortex field 17 neurons, these being sensitive to the shape and orientation of cross-shaped figures.

Animals↗
PubMed1981

Pattern reversal evoked potential amplitudes: life span changes.

Pattern reversal evoked potentials (PREPs) were recorded from people whose ages ranged from 4 to 90 years. Dramatic reductions in PREP amplitudes occurred between childhood and adolescence. These changes were most evident in females. Following adolescence there were no significant changes in amplitudes, even to old age. Latencies, on the other hand, have been shown to change most dramatically between adulthood and old age. PREP amplitudes and latencies, therefore, appear to provide different and unique information regarding development and aging. One cannot ignore PREP amplitudes without sacrificing information regarding early development.

Adolescent↗
PubMed1982

Normal checkerboard pattern reversal evoked potentials in parkinsonism.

The utility of checkerboard pattern reversal visual evoked potentials in the evaluation of Parkinson disease (Pd) was studied in 25 patients and controls without eye pathology. The results did not reveal differences in potential latency but the amplitude appeared slightly larger in PD than controls. Major intraocular differences were observed only in Pd patients with glaucoma, cataracts or retinal degeneration. The commonly employed high contrast and luminance, checkerboard pattern reversal technique did not appear useful in the evaluation of Pd. Selection of proper stimulus parameters may be critical in detecting VEP abnormality in Pd.

Aged↗
PubMed1986

Effect of central scotomata on pattern reversal visual evoked potentials in patients with maculopathy and healthy subjects.

The effect of central scotomata on pattern reversal visual evoked potential (PVEP) was investigated in patients with maculopathy and healthy subjects. PVEP was evoked monocularly by both full-field and half-field stimulations. Since the latency of 'the major positivity at Oz' (P100-Oz) is used as the most reliable parameter in the clinical application of PVEP, special attention was focused on its changes, comparing with 'ipsilateral major positivity of half-field PVEP' (P100-IHF). Although the incidence of modification was lower in the patients, central scotomata modified PVEPs of the healthy subjects and of the affected eye of the patients in a similar manner: full-field PVEP showed prolonged latency and reduced amplitude of P100-Oz. Half-field PVEP disclosed prolonged P100-Oz latency with intact P100-IHF latency. Only difference was that amplitude reduction of both P100-Oz and P100-IHF of half-field PVEP was observed only in the healthy subjects. The prolonged P100-Oz latency of half-field PVEP was accompanied, both in the healthy subjects and in the patients, by a contralateral negative-positive complex (N105-P135) which was augmented and extended to Oz. The prolonged P100-Oz latency, thus, was due to the pronounced P135. These observations suggested that an attenuation of the afferent impulses from the central retina may cause a prolongation of the P100-Oz latency in both healthy subjects and patients, but this is not a reflection of the truly prolonged P100-IHF latency. It was concluded that, in the clinical application of PVEP, recordings of half-field PVEP from the lateral electrodes seem to be essential to distinguish true prolongation of the P100-Oz latency.

Adolescent↗
PubMed1994

Dynamics of cognitive brain dysfunction in patients with cirrhotic liver disease: an event-related P300 potential perspective.

The dynamics of cognitive brain functions of 104 patients with both chronic non-cirrhotic (NC) and cirrhotic liver disease (C: C1, non-encephalopathic; C2, encephalopathic) were investigated by means of visual P300 potentials elicited in both the paradigms of transient (PI) and selective attention (PII). Conventional PVEPs, psychometric tests and quantitative liver function tests were also performed. As compared to both an age-matched control group (N) and the non-cirrhotic patients (NC), the N250 and P300 latencies of the cirrhotics (C) were equally prolonged in both P300 paradigms (P = 0.0001). By contrast, the P300 amplitudes were not different between the patient groups in either P300 paradigm. In the cirrhotics, however, the P300 amplitude differences between PII and PI (+ 3.7 +/- 2.8 muV, mean +/- 1 S.D.) were significantly (P < 0.01) smaller than in the non-cirrhotics (+ 7.5 +/- 5.2 muV) reflecting disturbances in the dynamics of visual attention. Interestingly, these P300 amplitude differences between both paradigms were positively correlated (r = 0.35; P = 0.005) with hepatic metabolic capacity, but not with liver blood flow (r = 0.23; P > 0.05). The diagnostic efficacy of the visual P300 in PI (sensitivity, 48%; specificity, 100%) was lower than that of the visual P300 in PII (79%; 100%) and that of the psychometric tests (63%; 94%), but it remained superior to that of the PVEPs (29%; 97%). It is concluded that in patients with cirrhotic liver disease visual P300 potentials can even reveal the dynamics of minor cognitive brain dysfunction and may also provide interesting pathophysiological information.

Adult↗
PubMed1988

Event-related potentials and the matching of familiar and unfamiliar faces.

Event-related potentials (ERPs) were recorded from one midline and three pairs of lateral sites while subjects made same/different judgements on sequentially presented pairs of familiar or unfamiliar faces. During the interval between the first and second face, a slow wave was more negative-going over the right than the left hemisphere, particularly when the faces were familiar. Following the second face, two regions of the waveforms were more negative-going when this face did not match the identity of its predecessor. In the early region (less than 160 msec), this effect was confined to posterior electrode sites and familiar faces. In the later region (greater than 250 msec), the match/non-match effect was widespread across the scalp and was evident for both familiar and non-familiar faces, although in the latency range 350-450 msec (encompassing the "N400" component), it was greater in magnitude in the case of familiar stimuli. It is suggested that the slow wave asymmetries reflect the engagement of short-term memory mechanisms lateralized to the right hemisphere. The match/non-match differences are thought to reflect multiple processes, including the modulation of the "N400" component. The sensitivity of this component to the familiarity manipulation is consistent with the hypothesis that the amplitude of N400 reflects an item's compatibility with currently activated memory representations.

Adult↗
PubMed1988

Context effects on saccade-related brain potentials to words during reading.

In two experiments saccade-related brain potentials (SRPs) to sentences were investigated under conditions approximating natural reading. Our aim was to look for electrophysiological (SRP) signs of sentence context on the processing of final words that were either congruent or incongruent with the meaning of the sentence. In Experiment 1 subjects indicated by a button-press whether or not the final word was congruent with the context, while in Experiment 2 they read silently without an overt decision. In Experiment 1, SRPs to incongruent words were more negative than SRPs to congruent words between 80-310 msec (from saccade offset). In Experiment 2, however, the inconcruent SRPs became more negative than the congruent SRPs only between 280-460 msec. These results suggest that in Experiment 1, during the processing of incongruent words the early sign of registering mismatch appears simultaneously with the analysis of the visual features of the word.

Adult↗
PubMed1983

Evoked potential contrast sensitivity in the parafovea: spatial organization.

Visual evoked potential contrast sensitivity functions (VEP/CSFs) were determined for counterphase flickered sine-wave gratings in circular fields up to 8 degrees in diameter centered on the fovea. VEP sources responding to 16 c/deg gratings appeared to be concentrated in the central 2 degrees of the visual field while sources responding to lower spatial frequencies appeared to be distributed over progressively wider areas of the visual field as spatial frequency decreased. It was also found that independently determined VEP/CSFs for non-overlapping annular regions of the visual field centered on the fovea summed to equal the VEP/CSF obtained when both regions were stimulated simultaneously.

Evoked Potentials, Visual↗
PubMed1985

Lateral actions at the inner plexiform layer of the carp retina: effects of turning windmill pattern stimulus.

Lateral action from amacrine to ganglion cells was studied in the isolated carp retina by using a truncated windmill pattern (TWP). About 25% of ganglion cells of both "on" and "off" center types were suppressed or enhanced in firing activity in response to TWP turning. The suppressed cells were more sensitive to slow turning velocities of TWP than the enhanced cells. In the "on-off" type amacrine cells, a steady depolarizing or hyperpolarizing component (less than several mV) was maintained by stationary TWP, while the cells were exclusively depolarized by turning TWP at a wide range of velocities. These results suggest that individual responses of ganglion cells induced by both stationary and turning TWP are depending on a balance between two factors: the polarizing direction of steady components of the "on-off" amacrine cells and the polarizing direction of ganglion cells synaptically produced by the amacrine cells.

Action Potentials↗
PubMed1985

Flicker and movement constituents of the pattern reversal response.

A counterphase-modulated (i.e. contrast reversing) pattern will affect hypothetical neural elements sensitive to motion as well as hypothetical elements sensitive to changes in contrast and other elements sensitive to local luminance. Attempts to describe visual evoked potentials (VEPs) to contrast reversal entirely in terms of luminance change or entirely in terms of contrast change have been unsuccessful; strong interactions between responses to contrast decrease and increase had to be postulated ad hoc in order to account for the contrast reversal VEP, and no explanation for these interactions has been proposed. Rather than attempting to separate the reversal VEP into responses to contrast decrease and increase, we attempt here to analyze the reversal VEP into responses to motion onset and offset. We find that VEPs to an abrupt displacement of less than one square's width of a checkerboard pattern are qualitatively similar to the contrast reversal VEP, and that the displacement VEP can be seen as the limiting case of a motion onset response shortly followed by a motion offset response. When displacement occurs during steady motion, the displacement and motion responses interact. We conclude that the contrast reversal VEP is better described in terms of motion onset and offset response than in terms of contrast onset and offset responses.

Adaptation, Ocular↗
PubMed1985

Neural interactions of two moving patterns in the direction and orientation domain in the complex cells of cat's visual cortex.

An examination was made of the responses of complex cells in cat's striate cortex to a textured (nonoriented) stimulus moving in the preferred direction, superimposed upon either a textured or a grating stimulus (oriented) that was moved in different directions. The cell discharges elicited by the textured stimulus moving in the preferred direction were reduced by the textured stimulus moving in nonpreferred directions, and increased when moved in the preferred direction. A grating moving in nonpreferred directions showed similar inhibitory effects on the responses to a textured stimulus moving in the preferred direction. Neural processing for directional movement is, therefore, affected by other neural processing for directional movement, and still more by that for orientation.

Animals↗
PubMed1986

Horizontal cell signal is smaller with texture-like nonuniform patterns than with uniform fields of the same space-average illuminance.

While measurement of the pertinent response as a function of flash intensity has been a standard procedure in vision research, we ask here what happens to horizontal cells in the vertebrate retina if the flash energy is varied through the density of a large number of small light spots rather than through the intensity of uniform illumination. The experiment described here demonstrates that the electrical response of horizontal cells in the turtle retina is consistently smaller with the present dot-density modulation than with the usual intensity modulation, even though the comparison is made when the mean irradiance per photoreceptor is equal in the two methods of modulation. Thus, the spatial summation, an important retinal function often thought to provide a base signal level for contrast detection, is affected significantly by how the visual pattern is structured at a level of microscopic dimension far smaller than the receptive field. The present finding, which seems to be a new form of area-intensity effect, can be explained if the dendritic membrane conductance of horizontal cells at each synaptic site increases at a progressively higher rate with decreases of the corresponding local illuminance. This possibility is discussed in the light of relevant photoreceptor response data, the presumed sigmoidal trend of the postsynaptic chemosensitivity and a simple electrical analog of contiguous horizontal cells.

Animals↗
PubMed1986

The importance of eye movements in the analysis of simple patterns.

How important are eye movements to visual pattern analysis? Previous findings indicate that at least one visual task (counting) is seriously impaired without them. We asked whether a comparable limitation applies to pattern recognition. Subjects were presented with pairs of randomly generated arrays composed of black and white pixels. The subjects indicated whether the arrays were identical or differed by one pixel. In one experiment, they were instructed to use normal eye movements, in another they were required to fixate on a point between the arrays. When eye movements were permitted, subjects' performance showed evidence for a search in which the discrepant pixel was eventually found, given adequate inspection time. When fixation was required, search was less efficient and the discrepant pixel was sometimes not found, despite prolonged inspection time. These results were independent of target size over a wide range. Our findings indicate that eye movements play a crucial role in pattern analysis that is not related to resolution.

Eye Movements↗
PubMed1987

Influence of saccades on manual reactions--a reaction time and VEP study.

Experiments were performed to investigate the retardation of motor reactions, triggered immediately after saccadic eye movements, by comparing VEP latencies and manual reaction times. As visual stimuli grating patterns of different spatial frequencies were used. They were presented during continuous fixation ("resting eye" condition) as well as shortly after a saccade ("saccadic" condition) with different onset delays (25, 50, 100, 150 msec), in order to determine the influence of saccades on VEP latencies and on manual reaction times. Compared with the reaction times in the "resting eye" condition, the postsaccadic reaction times were much prolonged whereas the respective VEP latencies are almost unchanged. Thus an inhibitory interaction of different motor responses (i.e. saccadic eye movements and manual reactions in this study) at higher levels of the afferent system or at the motor control site is postulated. This result has been confirmed for stimuli of different spatial frequencies.

Evoked Potentials, Visual↗
PubMed1988

Evoked potential estimates of the time course of adaptation and recovery to counterphase gratings.

Scalp-recorded evoked potentials (VEP) were sequentially sampled in humans during adaptation to and recovery from prolonged viewing of counterphase sinusoidal grating targets. The sum of the power at the first and second harmonics of the Fourier-transformed VEP components was found to decrease during adaptation and increase during recovery. Time constants (T) for the adaptation and recovery processes as estimated from exponential functions ranged from 2.9 to 19 sec, varying non-monotonically with the spatial frequency and contrast of the stimulus. The observed T values are shorter than those reported in psychophysical studies of adaptation but overlap estimates derived from single cell studies. An unexpected finding was the occurrence of a 3-6 sec delay in the appearance of the maximum VEP response after the onset of the adaptation stimulus. The delay occurred in all subjects and at all spatial frequencies when moderate to high adapting contrasts (e.g. greater than 0.2) were used. The data support a feature-selective, multi-channel lateral inhibitory model of spatial vision and suggest the presence of tonic inhibition between the channels.

Adaptation, Ocular↗