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PubMed2001

A first comparison of the human multifocal visual evoked magnetic field and visual evoked potential.

Our objectives were to determine the feasibility of recording reliable multifocal visual evoked magnetic fields (mfVEFs), to investigate the maximum stimulus eccentricity for which the mfVEF responses can be obtained, and to study how this changes with checksize (spatial frequency tuning). Using a checksize of 30', we recorded 8-channel pattern-onset mfVEFs three times to obtain responses from 19 channels located around the inion. Multifocal visual evoked potentials (mfVEPs) were recorded under the same conditions. Eccentricity changes with spatial frequency were studied using checksizes from 7.5' to 60'. We obtained, for the first time, reliable mfVEFs, and found they could be elicited from more peripheral stimulus elements than could mfVEPs. The larger the checksize, the greater the eccentricity reached.

Adult↗
PubMed2003

Visual backward-masking deficits in schizophrenia: relationship to visual pathway function and symptomatology.

Patients with schizophrenia have information processing deficits which can be measured using visual backward-masking (VBM) tasks. There are two types of visual pathways: transient and sustained. The former is more sensitive to low spatial frequency (LSF) and the latter to high spatial frequency (HSF) stimuli. It has been hypothesized that the VBM deficit in schizophrenia is due to an overactive transient channel response to the mask. To examine this hypothesis, patients with schizophrenia and comparison volunteers were tested on a traditional backward-masking task as well as on tasks that altered the mask to bias stimulation toward transient (LSF) or sustained (HSF) channels. Medication effects and relationship to symptomatology were also examined. Patients with schizophrenia showed a significant deficit on the traditional backward-masking task and were also significantly impaired on the LSF- and HSF-masking tasks, though a differential deficit was not found on the latter two tasks. A U-shaped function, indicative of masking by interruption, was found on the LSF- and HSF-masking tasks. Masking performance was not altered when the same patients were tested on and off medication, and performance was related to positive and negative symptoms. In conclusion, the finding of a deficit in patients with schizophrenia on tasks producing a U-shaped function suggests that an aberrant transient response to the mask is producing increased interruption of the sustained response to the target.

Adult↗
PubMed2000

Visual contrast response functions in Parkinson's disease: evidence from electroretinograms, visually evoked potentials and psychophysics.

OBJECTIVES: Visual contrast detection thresholds and suprathreshold contrast discrimination thresholds were compared to luminance and flash/pattern electroretinograms (ERG) and visually evoked potentials (VEP) in patients with Parkinson's disease (n = 31), patients with multiple system atrophy (n = 6), patients with progressive supranuclear palsy (n = 6) and control patients without central nervous disease (n = 33). METHODS: The stimuli were luminance modulated full-field (flash) or horizontally oriented sinewave gratings (pattern), the latter having either a low (0.5 cycles/deg) or medium (4.0 cycles/deg) spatial frequency. Stimulus contrast ranged from 10 to 80% so that contrast response functions could be derived. RESULTS: Contrast thresholds were higher in the patients with Parkinson's disease than in the control patients. Contrast discrimination thresholds were also somewhat elevated in patients with Parkinson's disease. Pattern ERG amplitudes were significantly reduced in patients with Parkinson's disease for the medium spatial frequency stimulus, but less for the low spatial frequency and flash stimuli. CONCLUSIONS: Our results suggest that Parkinson's disease impairs contrast processing in the retina. VEP amplitudes did not significantly differ between the groups for the conditions tested. Patients with progressive supranuclear palsy also showed impaired contrast perception and reduced ERG amplitudes, whereas patients with multiple system atrophy were less impaired.

Aged↗
PubMed2002

Pattern-reversal visual evoked potentials in infants: gender differences during early visual maturation.

This paper investigates gender differences in the peak latency and amplitude of the P1 component of the pattern-reversal visual evoked potential (pattern-reversal VEP) recorded in healthy term infants. Pattern-reversal VEPs in response to a series of high contrast black and white checks (check widths 120', 60', 30', 24', 12', 6') were recorded in 50 infants (20 males, 30 females) at 50 weeks post-conceptional age (PCA) and in 49 infants (22 males, 27 females) at 66 weeks PCA. Peak latency of the major component, P1, was considerably shorter in female compared with male infants. Differences in head circumference do not entirely account for the gender differences in peak latency reported here. A gender difference in P1 amplitude was not detected. These findings stress the importance of considering gender norms as well as age-matched norms when utilizing the pattern-reversal VEP in clinical investigations. Studies including a wider range of ages are clearly necessary in order to establish whether the earlier peak latencies in female infants represents a difference in the onset or rate of visual maturation.

Age Factors↗
PubMed1990

Spatial and temporal analysis by neurons in the representation of the central visual field in the cat's lateral suprasylvian visual cortex.

We studied quantitatively the receptive-field properties of 74 units recorded from the representation of the central visual fields in the cat's lateral suprasylvian (LS) visual cortex. In agreement with previous workers, we found that LS receptive fields tended to be large and to lack discernible spatial structure. They resembled the complex receptive fields of areas 17 and 18 in their general organization. We examined the responses of these neurons to moving optimally oriented sinusoidal gratings that varied in spatial and temporal frequency of drift. Most LS neurons were selective for the spatial frequency of sinusoidal gratings; 7% responded to all spatial frequencies below a cutoff value. In agreement with previous reports, the optimal spatial frequencies for LS neurons covered a wider range than is seen in either area 17 or 18 alone (0.05-1 cycle/deg), but are certainly included in the range covered by both these afferent areas. Individual neurons in LS responded to a range of spatial frequencies broader than is typical for neurons in areas 17 and 18. The effect of varying the drift rate of otherwise optimal gratings was similar in LS to that reported for areas 17 and 18. Most neurons were optimally responsive to drift rates between 0.5 and 4 Hz, and resolved frequencies as high as 10-30 Hz. A few neurons had optima higher than 6 Hz and resolved frequencies in excess of 30 Hz. We conclude that the receptive fields of LS neurons reflect rather closely the properties of their afferents from areas 17 and 18.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1998

Cytidine-5'-diphosphocholine improves visual acuity, contrast sensitivity and visually-evoked potentials of amblyopic subjects.

PURPOSE: Cytidine-5'-diphosphocholine (CDP-choline) therapy is currently used to improve the consciousness level in patients with brain lesions and as a complement to levodopa therapy in Parkinson's disease. Recently, the substance has been shown to improve the visual acuity (VA) of both eyes of adults with amblyopia. This study aims at establishing whether Contrast Sensitivity (CS) and visually-evoked potentials (VEPs) also change after CDP-choline treatment. METHODS: VA, CS, and VEPs were measured in a group of amblyopic volunteers (n = 10, mean age 24.8 years) before treatment with Neuroton (CDP-choline, 1 g/day intramuscularly [IM] for 15 days) and the day after termination of the same. CS was evaluated, using a forced-choice, automatic procedure (QUEST: Watson and Pelli, 1983). Steady-state VEPs were recorded in response to counterphased (8 Hz) sinusoidal gratings (2 c/deg) of different contrasts. RESULTS: On average, after treatment, VA improved 1.4-1.5 lines in the amblyopic eyes and 0.4 lines in the normal eyes. CSs improved in both dominant and amblyopic eyes by about 3 dB. VEPs increased in amplitude (about 30%) and advanced in phase (about 0.2 pi rad). Amplitude and phase changes were not correlated. CONCLUSIONS: Treating adult amblyopes with CDP-choline has the effect of improving their VA, CS and VEPs. Changes occur in both eyes, although to different extents, and resemble those previously reported for levodopa treatment.

Adolescent↗
PubMed1994

Learning disability subtypes and the effects of auditory and visual priming on visual event-related potentials to words.

Three learning-disability (LD) subtype groups and a normal control group of children were compared in their visual event-related potentials (ERPs) to primed and unprimed words. The LD subtypes were defined by deficient performance on tests of arithmetic (Group A), reading and spelling (Group RS), or both (Group RSA). The primed words were preceded by pictures or spoken words having a related meaning, while unprimed words were preceded by non-associated pictures or spoken words. For normal controls, N450 amplitude was greater to unprimed words than to words primed by pictures and spoken words. For Group A, N450 amplitude was reduced by spoken-word primes, but not by picture primes, an effect that demonstrates a deficit in processing visual-spatial information. For Group RS and Group RSA, neither picture nor spoken-word primes reduced N450 amplitude. These effects can be understood in terms of deficiencies in processing auditory-verbal information. Normal controls displayed a greater left- than right-hemispheric asymmetry in frontal N450 amplitude to unprimed words, an effect that is consistent with the association of skilled reading with hemispheric specialization. This asymmetry was absent in the ERPs of all the LD subtypes. The distinct ERP effects for the groups endorses the value of defining LD subtypes on the basis of patterns of deficits in arithmetic and reading and spelling.

Adolescent↗
PubMed1981

Inherent characteristics of visual stimulus systems and their effect on the visual evoked potential.

The inherent stimulus characteristics of three common types of visual stimulus systems, based upon a slide projector, a television and a photic stimulator, were measured. The effect of these characteristics upon pattern visual evoked potentials (VEPS) elicited by the systems was also investigated. Considerable differences in both spatial and temporal luminance characteristics were found between the systems. The differences in spatial luminance properties produced no significant changes in the VEP waveform, but the temporal luminance properties of the television system, in particular, produced maleficent effects on the VEP. Methods of dealing with these problems and of overcoming some of the traditional disadvantages of a strobe stimulus are discussed.

Brain↗
PubMed1980

Central visual field contributions to the visual-evoked response.

Visual evoked responses (VER) were recorded from bipolar electrodes placed transversely across the occipital region. A series of apertures were used to block the stimulation of the foveal area. The transverse distribution of the C2 component of the VER corresponds to a radial dipole source, and this is consistent with a foveal origin in the visual cortex. A clinical test for the presence of intact foveal projection, when opaque media preclude more conventional tests, could employ the VER.

Computers↗
PubMed2006

Normal age-related sensitivity loss for a variety of visual functions throughout the visual field.

PURPOSE: The purpose of this study is to compare the rate of age-related decline, the magnitude of practice effects, and test-retest variability among normal subjects using six different tests of visual function. METHODS: One hundred normal subjects aged between 20 and 85 were enrolled in the study. Six visual field test procedures were used consisting of standard automated perimetry (SAP), short wavelength automated perimetry (SWAP), temporal modulation perimetry (TMP), frequency-doubling technology perimetry (FDT), detection acuity perimetry (DAP),and resolution acuity perimetry (RAP). To facilitate direct comparison, the results for each test were divided by that test's estimated dynamic range. RESULTS: Of the three tests used clinically most commonly, SWAP exhibited the greatest aging and practice effects and test-retest variability followed by FDT with SAP exhibiting the least. RAP was the most variable test followed by TMP. CONCLUSIONS: These results should be taken into account when evaluating glaucomatous loss using different functional tests and when comparing the performance, predictive power, and speed of detection of the different tests.

Adult↗
PubMed2004

Transfer of adaptation from visually guided saccades to averaging saccades elicited by double visual targets.

The adaptive mechanisms that control the amplitude of visually guided saccades (VGS) are only partially elucidated. In this study, we investigated, in six human subjects, the transfer of VGS adaptation to averaging saccades elicited by the simultaneous presentation of two visual targets. The generation of averaging saccades requires the transformation of two representations encoding the desired eye displacement toward each of the two targets into a single representation encoding the averaging saccade (averaging programming site). We aimed to evaluate whether VGS adaptation acts upstream (hypothesis 1) or at/below (hypothesis 2) the level of averaging saccades programming. Using the double-step target paradigm, we simultaneously induced a backward adaptation of 17.5 degrees horizontal VGS and a forward adaptation of 17.5 degrees oblique VGS performed along the +/- 40 degrees directions relative to the azimuth. We measured the effects of this dual adaptation protocol on averaging saccades triggered by two simultaneous targets located at 17.5 degrees along the +/- 40 degrees directions. To increase the yield of averaging saccades, we instructed the subjects to move their eyes as fast as possible to an intermediate position between the two targets. We found that the amplitude of averaging saccades was smaller after VGS adaptation than before and differed significantly from that predicted by hypothesis 1, but not by hypothesis 2, with an adaptation transfer of 50%. These findings indicate that VGS adaptation largely occurs at/below the averaging saccade programming site. Based on current knowledge of the neural substrate of averaging saccades, we suggest that VGS adaptation mainly acts at the level of the superior colliculus or downstream.

Adaptation, Physiological↗
PubMed1987

Subnormal visual acuity in children: prognosis and visual evoked cortical potential findings.

Seventy-one children, age 4-12 years, with subnormal visual acuity (VA) in at least one eye (0.7 or less) were examined using visual evoked cortical potentials (VECPs) to pattern-reversal stimulation. Twenty-eight children with squint had mean VA 0.3 in squinting and 0.7 in non-squinting eyes. Thirty-one children had unexplained subnormal VA, mean 0.6. Twelve children with mild unclassifiable fundus abnormalities had mean VA 0.5. In the squinting eyes and the eyes with fundus abnormalities the mean latency of the VECP was significantly prolonged. In squinters the mean amplitude to stimulation of the squinting eyes and to binocular stimulation was significantly reduced. Statistically significant increase in the mean VA was observed in all groups except in the cases with visible fundus abnormalities. There was no statistically significant correlation between VECP parameters and final VA. In conclusion, VA prognosis could not be predicted from VECP data in individual cases.

Child↗
PubMed1976

Visually evoked cortical potentials in the evaluation of homonymous and bitemporal visual field defects.

Visually evoked cortical potentials were studied in six patients with a homonymous and six with a bitemporal hemianopia by presenting a pattern-reversal stimulus separately to a temporal or nasal retinal area and by recording the responses from leads over the hemispheres. Homonymous visual field defects are characterized by a reduction of VECPs from the affected hemisphere. The disturbance of VECPs in bitemporal hemianopia is more serious, since the fibres from both retinal halves may be damaged by a chiasm tumour.

Evoked Potentials↗
PubMed1984

Evaluation of the Friedmann Visual Field Analyser Mark II. Part 2. Results from a population with induced visual field defects.

The Friedmann Visual Field Analyser Mark II is evaluated with a group of 301 normal eyes, 155 of which had an induced visual field defect. Measures of sensitivity and specificity are calculated from these data by criteria similar to those used by other researchers. The inadequacies of using pass/fail criteria in the clinical situation are discussed, and a solution is proposed in which each field response is scored and the score compared with those from normal and defective populations. An example is given of how this form of analysis could be incorporated into the clinical situation.

Evaluation Studies as Topic↗
PubMed2000

Epilepsy surgery, visual fields, and driving: a study of the visual field criteria for driving in patients after temporal lobe epilepsy surgery with a comparison of Goldmann and Esterman perimetry.

Twenty four patients who had undergone temporal lobe surgery for epilepsy were assessed to determine (a) whether or not they had developed a visual field defect and (b) if a field defect was present, were the visual field criteria, as required by the DVLA, fulfilled using the monocular Goldmann perimeter test and the automated binocular Esterman method performed on a Humphrey perimeter. A field deficit was found in 13 of 24 (54%) using the Goldmann perimeter and 11 of 24 (46%) by the Esterman method. The second was a more lenient assessment with six of 24 (25%) failing the driving criteria compared with 10 of 24 (42%) by the monocular Goldmann method. Three patients were seizure free but failed the driving criteria. This complication of surgery for temporal lobe epilepsy needs to be discussed with patients before surgery.

Adult↗
PubMed1981

Visual response properties of neurons in four extrastriate visual areas of the owl monkey (Aotus trivirgatus): a quantitative comparison of medial, dorsomedial, dorsolateral, and middle temporal areas.

1. The response properties of 354 single neurons in the medial (M), dorsomedial (DM), dorsolateral (DL), and middle temporal (MT) visual areas were studied quantitatively with bar, spot, and random-dot stimuli in chronically implanted owl monkeys with fixed gaze. 2. A directionality index was computed to compare the responses to stimuli in the optimal direction with the responses to the opposing direction of movement. The greater the difference between opposing directions, the higher the index. MT cells had much higher direction indices to moving bars than cells in DL, DM, and M. 3. A tuning index was computed for each cell to compare the responses to bars moving in the optimal direction, or flashed in the optimal orientation, with the responses in other directions or orientations within +/- 90 degrees. Cells in all four areas were more sharply tuned to the orientation of stationary flashed bars than to moving bars, although a few cells (9/92( were unresponsive in the absence of movement. DM cells tended to be more sharply tuned to moving bars than cells in the other areas. 4. Directionality in DM, DL, and MT was relatively unaffected by the use of single-spot stimuli instead of bars; tuning in all four areas was broader to spots than bars. 5. Moving arrays of randomly spaced spots were more strongly excitatory than bar stimuli for many neurons in MT (16/31 cells). These random-dot stimuli were also effective in M, but evoked no response or weak responses from most cells in DM and DL. 6. The best velocities of movement were usually in the range of 10-100 degrees/s, although a few cells (22/227), primarily in MT (14/69 cells), preferred higher velocities. 7. Receptive fields of neurons in all four areas were much larger than striate receptive fields. Eccentricity was positively correlated with receptive-field size (r = 0.62), but was not correlated with directionality index, tuning index, or best velocity. 8. The results support the hypothesis that there are specializations of function among the cortical visual areas.

Animals↗
PubMed1994

Wide-field nondirectional visual units in the pretectum: do they suppress ocular following of saccade-induced visual stimulation.

1. Direction-selective neurons in the nucleus of the optic tract (NOT) provide motion signals for controlling ocular following responses. When stimulated at low temporal and high spatial frequencies of motion (slow speeds), these retinal-slip neurons produce directional responses. When stimulated by motion at high temporal and low spatial frequencies (the visual conditions during saccades) the spontaneous activities of the neurons are inhibited by motion in all directions. A second class of neurons in, or near, the NOT have large receptive fields, are nondirectional, and are tuned to detect the same spatial and temporal stimuli that induce nondirectional inhibition in the retinal-slip neurons. We suggest that the nondirectional cells provide an inhibitory input for the retinal-slip neurons and therefore prevent ocular following of the visual displacements that accompany saccades.

Animals↗