PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Pattern Recognition, Visual”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,027 records · Page 57Linked to original sources
PubMed1994

Visual evoked potentials to flash and pattern reversal stimulation after administration of systemic or topical scopolamine.

It has previously been shown that 0.6 mg of scopolamine produces a delay in the flash visual evoked potential of young normal volunteers, while the pattern-reversal response does not change in latency. Recent work has shown that this drug differentially affects parvocellular and magnocellular systems. To investigate this effect, two studies were performed. In the first study, 0.4 mg of scopolamine was injected intramuscularly into 11 young, healthy male volunteers who had fasted overnight. The visual evoked potential was recorded to both binocular flash stimulation and monocular pattern-reversal stimulation by means of a checker-board consisting of 56' checks in a 28 degrees field. Responses were recorded before administration of the drug and then 1, 2, 4 and 6 hours after administration. The scopolamine produced a slowing of the flash P2 latency of approximately 6 ms (p < 0.05) two hours after drug administration. There was no effect on the latency of the flash N2 or pattern-reversal N75 or P100. There was an increase in amplitude of the flash N2-P2 component 6 hours after drug administration and an increase in the amplitude of the N75 and P100 2, 4 and 6 hours after the drug. Further subjects were investigated with the use of topical administration of 0.125% scopolamine applied monocularly. In all studies the other eye acted as a control. The subjects were again young healthy volunteers. The visual evoked potential was recorded to both flash and pattern-reversal stimulation with a checkerboard consisting of 60' checks counterphasing at 2 Hz within a 5 degrees field. Results suggest that systemic scopolamine affects the tectal pathway but has no peripheral effect.

Administration, Topical↗
PubMed1993

Refraction changes during elevation of intraocular pressure by suction cup, their reflection in the pattern visual evoked cortical potential and their compensation.

Visual evoked cortical potential studies using pattern stimuli with the intraocular pressure raised artificially by the suction cup method have been reported. Possible changes in the refraction of the eye due to the method employed and their influence on the pattern visual evoked cortical potential have not been considered. Changes in the refraction of the eye during artificial intraocular pressure elevation and the influence of such changes on pattern visual evoked cortical potentials were studied. The refraction changes were found to depend on the shape of the suction cup. They could be compensated for by employing properly shaped suction cups and contact lenses. The behavior of amplitude and latency of the pattern visual evoked cortical potential at artificially elevated intraocular pressure with compensation for refraction changes has been studied and found to depend in a characteristic manner on ocular perfusion pressure.

Adult↗
PubMed1984

Pattern electroretinogram and visually evoked cortical potentials in glaucoma.

Electroretinograms (P-ERG) and cortical potentials (P-VECP) evoked by checkerboard patterns were examined in patients with defects of the ganglion cell and nerve fiber layers due to glaucoma. Only a few patients exhibited a prolonged latency in the P-VECP, whereas in the P-ERG all patients with papillary and visual field defects revealed a significantly attenuated amplitude. Since there is a substantial fluctuation in the assessment of papillary excavation and visual field, the P-ERG offers a further means of evaluating and follow-up of retinal function in glaucoma patients.

Aged↗
PubMed1987

Retinal receptive fields under different adaptation levels studied with pattern-evoked ERG.

The pattern-evoked electroretinogram (PERG) was studied in three normal subjects under different levels of adaptation using pattern onset-offset stimulation. The occurrence of a response maximum (spatial selectivity) in the onset response at a certain spatial frequency can be interpreted as reflecting the activity of neurons having antagonistic center-surround receptive fields and allows an estimation of receptive-field center sizes. The present data suggest that in the light-adapted state, the majority of receptive fields, dominating the response can be estimated to have center diameters of 6-13 min of arc. With increasing dark adaptation, the spatial selectivity shifts from high to low spatial frequencies over 1.3-2.4 octaves, indicating that large receptive fields are active in the dark and small fields in the light. The physiological mechanisms of these changes are discussed on the basis of findings obtained from single-unit studies.

Adaptation, Ocular↗
PubMed1989

Effect of levodopa on the human pattern electroretinogram and pattern visual evoked potentials.

Pattern electroretinograms (P-ERGs) and pattern visual evoked potentials (P-VEPs) were recorded at three luminance levels and five different check sizes in a group of 16 control subjects before and after the oral administration of levodopa. At the lower luminance levels, significant decrease in P-ERG and P-VEP latencies were found. For P-VEPs the latency changes occurred only at small check sizes. No changes were observed in control experiments without levodopa administration. Our results show that levodopa-induced changes even occur at the retinal level and support a dopaminergic involvement in light and dark adaptation. Our observations are in agreement with a VEP delay found in Parkinson's disease and with a VEP latency increase in rats after dopamine depletion.

Administration, Oral↗
PubMed1991

Visual dysfunction in treated schizophrenia suggested by visual evoked potentials from pattern-reversal stimulation.

Steady-state visual evoked potentials (steady-state VEPs) from pattern-reversal stimulations were compared in treated schizophrenic patients and normal subjects matched for sex and age. The VEP amplitudes were more variable in the patients than in the controls. Furthermore, the VEP amplitudes of the patients mostly showed little or no change when the check size was varied, in contrast to the controls who showed a marked check size effect. These results suggest that schizophrenics receiving drugs have dysfunction of the visual system, especially an inability to respond adequately to changes of visual information.

Adult↗
PubMed1996

Heterogeneity of information-processing alterations according to dimensions of depression: an event-related potentials study.

To identify alterations in elementary cognitive operations according to dimensions of depression, two stages of information processing, namely the response choice and the motor preparation stages, were explored using an event-related potential paradigm in two subgroups of depressed patients (retarded and blunted affect versus anxious-agitated and impulsive) compared to controls. Two results are common to all depressed patients: a slow encoding of stimuli (P1 wave) and a prolonged processing of stimulus-response compatibility (after P3b). This is compensated by a global velocity increase in stimulus evaluation or decision making (P3b) in anxious-agitated patients or, on the contrary, cumulated with its velocity decrease in retarded-blunted-affect patients. Such results could provide an explanation for the massive retardation observed in blunted-affect patients, contrary to anxious-agitated patients, whose normal reaction times may come from a very high energetical involvement at the P3b level. Results as a whole suggest that impairments in blunted-affect patients concern effort mechanisms, whereas those in anxious-agitated patients concern perceptual processes.

Adult↗
PubMed1983

Developmental changes in the human visual system as reflected by the latency of the pattern reversal VEP.

Pattern reversal visually evoked potentials (VEPs) were recorded from 439 infants and young children ranging in age from 1 month to 5 years in response to large and small checks. Qualitative analysis of the VEP wave form showed that the first major positive component, P1, is consistently present at all ages, while the frequency of occurrence of later positive components is more variable. The proportion of infants showing late positive components increases with age; by 1 year, the frequency of occurrence of late components for large checks is more adult-like than for small checks. The latency of P1 was analyzed quantitatively. Results showed that P1 latency decreases rapidly during the first year of life for both large and small checks and that the time course of the latency change differs as a function of check size. VEPs to large checks attain adult-like P1 latency values by about 1 year of age, while the P1 latency of VEPs to small checks has still not reached adult levels by 5 years of age. Data from 12 infants tested longitudinally between 1 and 7 months of age using both checkerboards and square wave gratings show no difference in P1 latency between checkerboards and gratings comprised of large (30-240 min) pattern elements, but for patterns with small (7.5 and 15 min) elements, P1 latency to checks is significantly longer than P1 latency to stripes. These results are explained on the basis of the difference in the fundamental spatial frequency between checks and stripes.

Attention↗
PubMed1983

Perimetry, visual evoked potentials and visual evoked spectrum array in homonymous hemianopsia.

Confrontation field examination, perimetry, visual evoked potentials (VEPs) to pattern hemi-field stimulation and visual evoked spectrum array to flash stimulation were compared in 50 patients with homonymous hemianopsia. Visual field could be examined by confrontation in all patients and demonstrated the field defect in 96% of cases. Goldmann perimetry could only be performed in 60% of patients, but always quantitatively defined the margins of the defect. VEPs could only be tested in 77% of patients and demonstrated an abnormality in 79% of cases. VEPs were absent to stimulation of the affected hemifield in every case of homonymous field defects with macular splitting. Visual evoked spectrum array could be tested in 95% of patients and revealed abnormalities in 67% of cases. The relative value of each test is discussed.

Adult↗
PubMed1983

The effect of background illumination on pattern onset visual evoked potentials.

The early part (first 200 msec) of pattern onset VEPs elicited by a dartboard pattern was studied in conditions of varying level of background illumination. The effect of pattern adaptation and pattern blurr was also studied. The observed complex behaviour of the main negativity within this part of the VEP can be best described in terms of a composite of two independent negative peaks labelled N100 and N130. In high luminance conditions peak N100 was dominant and the presence of N130 was indicated only by a 'notch' on the rising slope of the negativity. As luminance decreased the situation was reversed and N130 became a dominant feature of the negative wave. This finding did not depend on the particular choice of reference site. For checkerboard stimulation the same features were present, but variability of the VEP wave form was greater than in the case of dartboard stimulation. Present results relate the well-known pattern specific properties of the negativity in onset VEPs to N100 only, whereas N130 is not pattern specific. Lower and upper half-field stimulation produced peaks of opposite polarity at 100 msec but no change was observed in polarity of N130. These findings support the suggestion that these two parts of the negativity in pattern onset VEPs may have different cortical sources.

Adaptation, Physiological↗
PubMed1983

Pattern-reversal visual evoked potentials in patients with chronic renal insufficiency.

Visual evoked potentials (VEPs) were recorded from 88 patients with chronic renal insufficiency twice at a 6 month interval. In dialysed patients statistically significant decreases in amplitudes and prolongations of VEP peak latencies were found. Azotaemic non-dialysed patients showed related, but smaller, changes in their VEPs. In patients after kidney transplantation the VEP amplitudes were normal but peak latencies were prolonged. No systematic significant relationship between the VEPs and creatinine and urea levels in the blood could be shown.

Brain↗
PubMed1994

Do patients with Down's syndrome recognize Mickey Mouse?

In 47 patients with Down's syndrome who were too retarded to understand a conventional oddball paradigm, we studied event-related potentials (ERPs) by using task-irrelevant visual stimuli. As the patients had expressed interest in Disney cartoons and books, five pictures of Disney characters such as Mickey Mouse or Peter Pan were employed as the rare stimuli, and nine ordinary scenes such as mountains as the frequent stimuli. Five sets were constructed by intermingling each rare picture with nine frequent pictures, and each picture was presented on a TV screen. ERPs to the rare stimuli (N270-P380), which were different from the averaged waveforms to frequent stimuli and electrooculograms (EOGs), were clearly recorded in 35 out of 47 patients. Only 24 of these patients had ERPs using a conventional auditory oddball paradigm. The peak latencies in patients were significantly prolonged relative to age-matched normal controls, probably due to a slowed neural processing. The amplitude in patients was slightly larger than normal controls, probably due to the patients' greater interest or surprise when confronted with the Disney characters.

Adolescent↗
PubMed1988

Systemic 1-methyl,4-phenyl,1-2-3-6-tetrahydropyridine (MPTP) administration decreases retinal dopamine content in primates.

Following MPTP administration, 4 Cynomolgus monkeys developed a parkinsonian syndrome, accompanied by specific changes of both pattern visual evoked potential and electroretinogram. Retinal dopamine and dihydroxyphenylacetic acid contents were measured in the 4 MPTP-treated monkeys and in 3 normal monkeys. Dopamine and dihydroxyphenylacetic acid levels were significantly lower in the retinas of the MPTP-treated animals (p less than 0.001), suggesting that dopamine has a specific function in the visual system of primates.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗
PubMed1988

Hemispheric differences for visual evoked potentials from checkerboard stimuli.

Visual evoked potentials (VEPs) were elicited in right-handed male subjects with an alternating checkerboard pattern stimulus presented to either the left or right visual half-field. The sizes of the individual checks in different conditions were 0.25, 0.5, 2.0, or 4.0 cycles/degree of visual angle. The amplitude of the P100 VEP decreased while peak latency increased as check size decreased across both visual field conditions. Left hemisphere responses demonstrated significantly larger P100 amplitudes compared to the right hemisphere responses, although the interaction between hemisphere and stimulus size was not significant. No hemispheric effects of P100 latency were observed. The results suggest that the left hemisphere is engaged more than the right hemisphere for the sensory analysis of visual stimuli composed of straight edges over a wide range of spatial frequencies.

Adult↗
PubMed1982

Steady state visual evoked potentials in the alert primate.

Macaque monkeys were trained to fixate a small spot while we recorded epidural steady state visual evoked potentials (SSVEP) in response to counterphase modulated sinusoidal gratings. This led to the following results: (1) the SSVEP can show either broad or narrow spatial frequency tuning, depending on electrode location, temporal frequency, contrast and method of analysis. (2) The SSVEP can also show narrow temporal frequency tuning, as narrow as 0.5 octave at half height. (3) Contrast functions relating VEP amplitude to log contrast were highly nonlinear. We propose that they are the composite of at least two distinct linear functions, one with a shallow slope for low contrasts and one with a significantly steeper slope for the higher contrasts. (4) Extrapolation of the low contrast function to zero voltage can lead to an excellent match with psychophysical functions. A similar extrapolation of the high contrast function, however, leads to a contrast value much higher than the psychophysical threshold. These findings suggest that the SSVEP can reflect the activity of two distinct neural mechanisms responsive to pattern stimulation. The degree to which either mechanism is evident determines the spatial and temporal frequency tuning of the VEP.

Animals↗
PubMed1985

Selectivity of the evoked potential for vernier offset.

Hyperacuity thresholds of a few arc seconds can be achieved psychophysically for a variety of spatial localization tasks. The present experiments show that evoked potentials can be elicited in response to the introduction of vernier offsets, but not by the introduction of other cues to hyperacuity such as bisection or relative pattern motion, although each of these cues is equally salient psychophysically. Moreover, vernier acuity measurements and the evoked potentials elicited in response to vernier offsets are strongly degraded by the introduction of flanking stimuli 2-4 min from the vernier target. This suggests that the hyperacuity VEP is a cortical correlate of a very specific type of hyperacuity, that produced by vernier offsets (colinearity failure).

Adult↗
PubMed1985

Spatial frequency sweep VEP: visual acuity during the first year of life.

The grating acuity of 197 infants from 1 week to 53 weeks of age was measured using the visual evoked potential (VEP) in response to counterphase grating stimulation. The gratings were presented as a 10 sec spatial frequency sweep which spanned the acuity limit. The amplitude and phase of the second harmonic response were extracted by discrete Fourier analysis. The VEP amplitude versus spatial frequency function showed narrow spatial frequency tuning with amplitude peaks at one or more spatial frequencies. The phase of the response at medium to high spatial frequencies was generally constant at a spatial frequency peak, followed by a progressive phase lag with increasing spatial frequency. Grating acuity was estimated by linear extrapolation to zero microvolts of the highest spatial frequency peak in the VEP amplitude versus spatial frequency function. This visual acuity estimate increased from a mean of 4.5 c/deg during the first month to about 20 c/deg at 8-13 months of age. The VEP acuities at 1 month are a factor of three to five higher than previously reported for pattern reversal or pattern appearance stimuli. By 8 months VEP grating resolution was not reliably different from adult levels in the same apparatus.

Adult↗