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 1,423 records · Page 79Linked to original sources
PubMed1981

The effect of stimulus orientation on the visual evoked potential in multiple sclerosis.

Visual evoked potential (VEP) latency was measured in 89 patients with multiple sclerosis (MS) using both a checkerboard stimulus and an alternating vertical grating. Thirty-seven patients had abnormal VEP latencies to the check stimulus, but 63 were classified as abnormal when the grating stimulus was employed. In an additional 22 MS patients, each eye was tested with a checkerboard stimulus, a vertical grating, and a horizontal grating to determine if edge orientation of the stimuli was responsible for the difference between grating and check diagnostic yields. The resulting diagnostic differences could be explained by taking into account the sinusoidal components of these stimuli. After equating gratings and checks for the fundamental Fourier component, each eye of 15 of the MS patients was retested with gratings in three orientations: vertical, horizontal, and oblique. Nine of the 15 patients had an orientation-dependent abnormality of VEP latency. The results suggest that MS causes an orientational imbalance in the human visual system and that VEP testing with stimuli in more than one orientation can increase the diagnostic yield in MS patients.

Adolescent↗
PubMed1990

Retinal origin of VECP delays as revealed by simultaneously recorded ERG to patterned stimuli.

Electroretinal and electrocortical potentials evoked by reversing checkerboards (PERG, PVECP) were simultaneously recorded in diseases of the central retina (10 patients) and in tumor-related optic nerve disorders (11 patients) exhibiting comparable P-100 delays in the PVECP. Retinal diseases showed a peak-time delay both in the PERG and in the PVECP, while optic nerve disorders revealed no delay in the PERG. Thus, simultaneous recording of PERG and PVECP may differentiate retinal from postretinal disorders of the visual system. The method also may provide information about the site of an underlying disorder in cases of visual disturbance without obvious changes of the ocular fundus.

Cranial Nerve Neoplasms↗
PubMed1992

Cortical potentials to pattern reversal and luminance onset under ramp stimulation conditions in glaucoma.

Stimulus quantities with a ramp-like temporal course evoke cortical potentials that are delayed and attenuated in comparison with responses evoked by a step-like course. This delay probably depends on temporal transfer characteristics of the activated precortical visual system. In a pilot study, luminance onset and pattern-reversal stimulation using this technique (light-emitting diode stimulator; transition time, 50 ms) were applied to 18 glaucomatous eyes with early visual field damage. The visual evoked cortical potential latency shifts between ramp and step mode were compared with visual field indices (mean defect, corrected loss variance). The pattern-reversal stimulation in ramp mode yielded a significant difference between the glaucoma group and normal subjects (p less than 0.004). The difference between groups with pattern-reversal stimulation in step mode was not significant (p = 0.15). From the determined visual field indices, only the mean defect showed a significant correlation to the measured visual evoked cortical potential latency shift, with both luminance-onset and pattern-reversal stimulation. In glaucoma with early malfunction, the precortical transmission and processing of lower and middle temporal frequencies, which are predominant in ramp-like temporal stimulus courses, are obviously more affected than the transmission of higher frequencies. The ramp stimulation technique for visual evoked cortical potentials might be of interest as a tool to detect early and specific functional defects in glaucoma.

Chronic Disease↗
PubMed1997

Comparison of preferential looking acuity and pattern reversal visual evoked response acuity in pediatric patients.

BACKGROUND: We compared the visual acuities obtained with preferential looking (PL), the most widely used method of pediatric vision assessment, with those obtained with the spatial frequency sweep pattern-reversal visual evoked response (SPVER). METHODS: Eighty patients (ages 1.5 months to 12 years) with various ocular pathologies participated in this study. The PL acuity was determined using the up-and-down staircase procedure. The PVER was recorded with the spatial frequency sweep method using 10 spatial frequencies; the acuity was determined by placing the best-fit regression line on the descending slope of the PVER amplitude-spatial frequency function toward the higher spatial frequency to the baseline. RESULTS: The PL acuities ranged from 20/25 to < 20/1600 (mean 20/155). The correlation between the two methods was good (r = 0.847). Fifty-six patients (70%) had an acuity agreement within 1.0 octave. When the PL acuity was > 20/128, it was on average better than the PVER acuity. When the PL acuity was lower, the PVER acuity was usually better. This tendency was marked when the visual acuities were very poor (y = 0.552x + 0.362). CONCLUSION: The methods correlate well, although there is a dissociation of acuities in the presence of very low vision. PVER may be a useful addition to PL in assessment of vision in infants and young children.

Child↗
PubMed1989

Miniature fiber-optic pattern-reversal stimulator for determination of the visual evoked potential threshold; comparison with Snellen acuity.

In this report we recommend the estimation of visual acuity by detection of the visual evoked potential (VEP) threshold, defined by the smallest visual angle of a constant check size that evokes potentials. This approach was implemented using a fiber-optic pattern-reversal stimulator placed at measured, increasing distances from the examined eye. Snellen visual acuity as determined in 113 subjects was correlated with the VEP detection threshold. A highly significant correlation was found between visual acuity and the threshold visual angle of check size in subjects whose vision was impaired due to opacity in ocular media. For any given visual acuity a somewhat wide range of threshold check sizes, typically 5-10 min of arc was observed. Technical difficulties that need to be overcome to improve these results are discussed.

Adult↗
PubMed1982

Chronic intraventricular administration of lysergic acid diethylamide (LSD) affects the sensitivity of cortical cells to monocular deprivation.

In kittens, but not in adult cats, depriving one eye of pattern vision by suturing the lids shut (monocular deprivation or MD) for one week reduces the proportion of binocular units in the visual cortex. A sensitivity of cortical units in adult cats to MD can be produced by infusing exogenous monoamines into the visual cortex. Since LSD interacts with monoamines, we have examined the effects of chronic administration of LSD on the sensitivity to MD for cortical cells in adult cats. Cats were assigned randomly to one of four conditions: MD/LSD, MD/No-LSD, No-MD/LSD, No-MD/No-LSD. An osmotic minipump delivered either LSD or the vehicle solution alone during a one-week period of MD. The animals showed no obvious anomalies during the administration of the drug. After one week the response properties of single units in area 17 of the visual cortex were studied without knowledge of the contents of the individual minipumps. With the exception of ocular dominance, the response properties of units recorded in all animals did not differ from normal. In the control animals (MD/No-LSD, No-MD/LSD, No-MD/No-LSD) the average proportion of binocular cells was 78%; similar to that observed for normal adult cats. However, in the experimental animals, which received LSD during the period of MD, only 52% of the cells were binocular. Our results suggest that chronic intraventricular administration of LSD affects either directly or indirectly the sensitivity of cortical neurons to MD.

Animals↗
PubMed1983

Interocular suppression in adults and infants using anaglyphic stimuli: visually evoked potential measures.

Interocular suppression, assessed by monocular VEP amplitude reduction, was investigated in 3 infants, average age of 3 months, and 8 adults. A dichoptic simultaneous masking paradigm was employed, the two eyes being disassociated by red and green filters which transmitted non-overlapping wave lengths of light (anaglyphic method). One eye was continuously presented with either darkness, a diffuse green light, or two green dot patterns, containing either 20' or 80' dots. The other eye was flashed with either red diffuse light, a red 20' dot pattern, or a red 80' dot pattern. In both adults and infants, monocular VEP amplitude was reduced as the size of the continuously presented dots increased (pattern suppression) and a smaller amplitude response occurred when dots of equal size were presented than when data of different size were presented (size-specific suppression). The relative and absolute magnitudes of interocular pattern suppression were similar for adults and infants. However, the relative and absolute magnitudes of size-specific suppression were larger for adults than for infants. Pattern interocular suppression was inferred to be relatively more mature in 3 month olds than size-specific suppression. The relative lack of size-specific suppression suggests a relative immaturity of binocular spatial frequency or size channels.

Adult↗
PubMed1985

Mechanisms of epileptogenesis in photosensitive epilepsy implied by the effects of moving patterns.

The triggering of epileptiform EEG discharges by pattern is thought to depend on the intensity of excitation within the visual cortex. The present study investigates the role of the synchronisation of neuronal activity by the stimulus. In 10 pattern-sensitive subjects the effects of the following patterns have been compared: (1) static gratings, (2) gratings oscillating in a direction orthogonal to the lines (which should synchronise activity in direction-sensitive cortical units), and (3) gratings drifting at the same angular velocity (which should produce little or no synchronisation, because the contours enter and leave the overlapping receptive fields of individual neurones asynchronously). The oscillating gratings were most, and the drifting least, epileptogenic. In 2 further subjects oscillating and phase-reversing patterns were more epileptogenic than drifting gratings. Although open to alternative explanations, the findings conform with predictions from the hypothesis that synchronisation of individual cortical neurones by the stimulus contributes to epileptogenesis in photosensitive subjects.

Adolescent↗
PubMed1985

Influence of L-DOPA/carbidopa on pattern reversal VEP: behavioural difference in primary and secondary parkinsonism.

Data obtained from a total of 246 monocular VEPs performed on 46 patients, 35 with Parkinson's disease and 11 with arteriosclerotic parkinsonism, classed in the first 3 stages on the Hohen and Yahr disability scale, are reported. Our data show a delay of mean P100 latency in the primary parkinsonian group during the period of washout from L-DOPA therapy as well as in the secondary parkinsonian group. But the interocular mean difference in VEP P100 results significantly increased in primary parkinsonism only. A more important different behaviour between primary and secondary parkinsonism concerns a possible reduction of VEP delay related to L-DOPA/carbidopa treatment. An improvement of P100 delay can be noticed after acute and after chronic DOPA therapy in primary parkinsonism only. The above data confirm previous reports concerning VEP delays in Parkinson's disease, suggesting monitoring of different pharmacological sensitivity in idiopathic and arteriosclerotic parkinsonian patients as a useful method.

Adult↗
PubMed1985

Dipole source derivation. Application to the half-field pattern evoked potential.

Dipole modelling is a technique for estimating the location of sources of electrical activity in the brain responsible for the generation of surface recorded potentials on the human scalp. A detailed description of this technique is given with a modification that allows for possible activity at the reference electrode during the surface potential measurement. The application of this technique to localisation of the source of the principal components of the left half-field pattern visual evoked potential is described.

Adult↗
PubMed1990

Cerebral correlates of imagining colours, faces and a map--II. Negative cortical DC potentials.

Cortical activation patterns as measured by negative shifts of the scalp-recorded cortical steady potential ("DC shifts") were assessed in 28 normal subjects during imagining colours, faces, and a spatial map. Imaging resulted in sustained negative DC shifts at temporal, parietal and particularly at occipital sites. The topographic distributions of such DC shifts was modulated as a function of whether spatial or visual imagery was performed. During imaging the spatial map, a parietal maximum was observed, as opposed to a distribution in favour of temporal and occipital sites during imagining faces and colours. Results suggest a neuroanatomical dissociation between visual and spatial imagery. Since a similar visual-spatial dichotomy exists in perception, the finding is interpreted as further evidence of a shared cerebral substrate for images and percepts. The results are discussed in conjunction with the joint blood flow study.

Adult↗
PubMed1993

Bilateral visual field processing and evoked potential interhemispheric transmission time.

The relationship between the efficiency of interhemispheric interactions via the corpus callosum and the speed and accuracy in making comparisons of information simultaneously presented to the right and left visual fields was studied by comparing bilateral (vs unilateral) advantages in matching letters, with evoked potential measures of interhemispheric transmission time (EP-IHTT). The primary finding was a strong correlation suggesting that larger bilateral field advantages in reaction time are associated with faster EP-IHTT. However, the association between EP-IHTT and bilateral advantage was strong only for transmission speed from left hemisphere to right hemisphere, but not for speed of transmission in the opposite direction. The data are consistent with a hypothesis of asymmetric homologue enhancement, i.e. a directionally asymmetric callosal influence which facilitates processing of letter stimuli in the right hemisphere allowing for increased response speed and accuracy of bilateral visual field comparisons.

Adolescent↗
PubMed1985

Complex visual textures as a tool for studying the VEP.

A method of separating components of the visual evoked potential by using complex visual textures is described. Interchange of visual textures with identical power specta and third-order autocorrelations elicits a response which may be analyzed into symmetric and asymmetric components. It is shown that the asymmetric component depends on complex attributes of form. Mechanisms that generate this component must possess nonlinear interactions among multiple areas of the visual pattern. These interactions are likely to be more complex than rectification following spatial summation. It is concluded that the asymmetric component reflects intracortical, rather than precortical, processing.

Adult↗
PubMed1985

The human visual evoked potential: analysis of components due to elementary and complex aspects of form.

The visual evoked potential (VEP) elicited by alternation between isodipole visual textures may be separated into an asymmetric and a symmetric part. The asymmetric part reflects processing of complex attributes of form. The spatial and temporal dependence of this response is used to evaluate models for the generation of this response. The symmetric part appears to reflect processing of local luminance and contrast changes. The relation of these components to the VEP elicited by contrast reversal, contrast modulation, and the windmill-dartboard stimulus is discussed.

Adult↗
PubMed1985

Neuropsychological basis of pattern vision in macaque monkeys.

The central mechanisms of underlying pattern vision in macaques (rhesus and Japanese monkeys) were investigated behaviorally and electrophysiologically. A series of studies indicated that there are two major processes underlying pattern vision. One of two processes is the process of attending selectively to pattern cues at background, with which inferior parietal cortex is concerned predominantly. The other is the process of pattern perception and cognition, in which inferotemporal cortex is involved closely.

Animals↗
PubMed1991

Spatial organization of nonlinear interactions in form perception.

We examined the perception of structure in a family of visual textures whose second-order correlation structure is flat. These textures were generated by two-dimensional recursion rules, in a manner which extends the construction of Julesz, Gilbert and Victor (1978; Biological Cybernetics, 31, 137-140). Textures generated by some recursion rules elicited a visually salient percept of structure, while textures generated by other recursion rules did not. Textures whose statistical structure was visually salient produced evoked responses which differed from the response evoked by completely random textures. The size of this VEP difference correlated well with psychophysical measures. Since the textures were constructed to have identical global spatial frequency spectra, models for the extraction of visual structure must be essentially nonlinear. Models based on symmetry, information content, or simple spatial extent (but not pattern) of correlation fail to explain the observed results. Models based on the cooperative interaction of pairs of nonlinear subunits provide a reasonable qualitative account of the findings. The critical model features are (i) the presence of multiple nonlinear subunits, and (ii) a second nonlinearity, such as a threshold, at the stage of combination of subunit signals.

Adult↗
PubMedDate not supplied

The pattern reversal VEP in short-gestation infants.

Visual evoked potentials (VEPs) to pattern reversal stimulation have been obtained in 10 premature babies. The babies were born between 32 and 35 weeks gestational age and had pattern reversal VEPs recorded on at least 2 separate occasions. The responses were obtained from 33 weeks gestational age, and all babies had their initial recording at or before 37 weeks gestational age. The pattern reversal stimulation was produced on a small hand-held television monitor. The black and white checks subtended a visual angle of 2 degrees. Flash VEPs were also recorded on each occasion for comparison. The pattern reversal response consisted of a major positive (P1) component around 280 msec. The latency of the P1 component correlated negatively with gestational age. Although the flash VEP in the same babies was often dominated by the initial negative component no similar negative components were seen in the pattern reversal response.

Evoked Potentials, Visual↗