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 1,297 records · Page 72Linked to original sources
PubMed1994

Prolonged latencies of pattern reversal visual evoked early potentials in Alzheimer disease.

We studied patients with Alzheimer disease, Parkinson disease, and amyotrophic lateral sclerosis (ALS) with a pattern reversal (checkerboard light diode) visual evoked potential (VEP) paradigm to observe the involvement of the visual system in these primary neurodegenerative diseases. All patients were in the mild or moderate stage of the disease. In Alzheimer disease there was a significant increase of the latency of the P55, N65, P100, and N130 components, as well as an increase of the P55-P100 interpeak latency, compared with matched normals. These alterations indicate dysfunction of both the retinocalcarine pathway and the cortex. Patients with Parkinson disease revealed a significant delay of the N130 component only. Patients with ALS had normal latency values of all VEP components. The P100-N130 amplitude was diminished in all these disease groups compared with age-matched controls.

Aged↗
PubMed1984

Foveal xenon flash disruption of steady-state visual evoked potentials.

The effects of foveal exposure to near maximum permissible levels of broad-band light from lamps of differing flash durations and visual angle subtense on steady-state visual evoked potentials ( SSVEP 's) were measured in four human volunteers. SSVEP 's in response to a counterphasing checkerboard pattern were recorded with a two-phase vector voltmeter used as an analog fourier analyzer and were averaged across repeated presentation of the flash from each lamp. Two microsecond flashes of approximately 0.4 degrees have minimal, although significant effects on early visual processing of a 2.77 degrees diameter 6/24 (20/80) target. Five hundred microsecond flashes of equivalent size have greater effects; larger flashes (11.3, degrees 500 mus) produced afterimages that totally obscured the target for approximately 3.4 s and also reduced the SSVEP to near zero. Recovery of the SSVEP was subjectively correlated with afterimage duration rather than target obscuration . Therefore, single short small retinal image flashes may have minimal transient effects on photopic suprathreshold vision.

Afterimage↗
PubMed2005

Abnormal activation of face processing systems at early and intermediate latency in individuals with autism spectrum disorder: a magnetoencephalographic study.

The neurological basis of developmental psychopathology in autism is a matter of intense debate. Magnetoencephalography (MEG) was used to study the neuronal responses associated with the processing of faces in 12 able adults with autism spectrum disorders (ASD), performing image categorization and image identification tasks. The neuromagnetic data were analysed using nonparametric time-series analysis and equivalent current dipole estimation. Comparison data were obtained from 22 normally developing adults. In individuals with ASD, the neural responses to images of faces, observed in right extrastriate cortices at approximately 145 ms after stimulus onset, were significantly weaker, less lateralized and less affected by stimulus repetition than in control subjects. Early latency (30-60 ms) responses to face images, over right anterior temporal regions, differed significantly between the two subject groups in the image identification task. No such difference was observed for images of mugs or meaningless geometrical patterns. These findings suggest that, during the course of development in individuals with ASD, the cortical activity associated with the processing of human faces assumes a different-from-normal localization in extrastriate brain regions. This abnormal localization may be associated with unusual, but nevertheless face-specific, fast processing pathways.

Adult↗
PubMed2005

Maturation of early visual processing investigated by a pattern-reversal habituation paradigm is altered in migraine.

Evidence for a disturbed maturation of information processing in migraine came recently from evoked and event-related potential studies during childhood. In adult migraineurs, deficient habituation is proposed as principal interictal abnormality and was found inter alia for Visual Evoked Potentials (VEPs). This study investigated response and habituation to pattern-reversal VEPs and its maturation in 102 children with primary headache (migraine with and without aura, tension-type headache) and 79 healthy controls from 6 to 18 years. A reduction of N180 latency from pre- to postpubertal age reflects maturation and was clearly present in controls but lessened in migraineurs. N180 latency was prolonged in migraineurs without aura from 12 years onwards. Habituation did not differ between groups. In conclusion, diminished N180 latency reduction with age in migraineurs gives further evidence that maturation of visual information processing is altered in migraine. Deficient habituation to pattern-reversal VEPs could not be confirmed during childhood migraine.

Adolescent↗
PubMed1994

Influence of caffeine on selective attention in well-rested and fatigued subjects.

Effects of caffeine were studied in a visual focused selective search task in well-rested and fatigued subjects. A dose of 200 + 50 mg caffeine or placebo, dissolved in decaffeinated coffee, was administered in a double-blind and deceptive fashion. The task was to detect a target letter on one diagonal of a visual display designated as relevant and ignore stimuli presented on the irrelevant diagonal. Behavioral measures were supplemented by event-related potential (ERP) measures. Subjects reacted faster in the caffeine condition. Caffeine enhanced the N1 and the N2b components. Selection of relevant information apparently was more adequate in this condition. Search negativity was not affected by caffeine. Caffeine effects on the P3 elicited by target letters were more pronounced in the fatigued than in the well-rested subjects, indicating that the effects of caffeine are dependent on the state of the subject. The results suggest that caffeine has specific rather than general effects on information processing.

Adolescent↗
PubMed1995

Diagnostic value of 33 Hz steady-state visual evoked potentials in low-vision children.

Pattern-reversal visual evoked potentials elicited by patterns of 60' and 20' checks and 33 Hz steady-state flash visual evoked potentials were recorded in low-vision children (visual acuity less than 20/120) with optic atrophy (18 eyes), amblyopia (18 eyes), macular degeneration (7 eyes) and controls (24 eyes). Steady-state visual evoked potentials were non-recordable in 17 out of 18 eyes of optic atrophy patients and normal in other children. Abnormalities of pattern-reversal visual evoked potentials were similar in all groups of patients. 33 Hz steady-state flash visual evoked potentials are recommended for differential diagnosis of optic atrophy with other causes of low vision in children.

Adolescent↗
PubMed1982

Clinical and experimental evidence that the pattern electroretinogram (PERG) is generated in more proximal retinal layers than the focal electroretinogram (FERG).

A TV monitor was used to evoke either a pattern ERG to a contrast-reversing checkerboard (PERG), or a focal ERG to alternate increases and decreases of luminance of the blank screen within a bright surround (FERG). Both responses are small (approx 2 microV) and fast (approx 50 msec to peak) and are similar in several other properties. However, they differ in timing and respond differently to changes in contrast. Each frame of a TV picture evokes a "raster ERG," even though the screen is blank. The response is focal and specific to a small central strip of the screen. It is simpler to record than the FERG, where the whole screen is flashing. Because the FERG summation area is about 4 deg, small squares (checks) reversing in contrast produce little luminance response. In 5 of 7 cases where the PERG is unilaterally reduced, the FERGs or raster responses were not affected. Thus clinical evidence also suggests that the PERG may be a separate phenomenon to the FERG and produced at a different site. Toxic, traumatic, congenital, and degenerative diseases of the optic nerve reduce the PERG. The comparison is most easily made in unilateral disease. Ten weeks after an optic nerve insult, the PERG becomes reduced in the affected eye as if retrograde degeneration was occurring. In 27 amblyopes of various types, the PERG was reduced in 23 where orthoptic treatment had failed. In 4 patients responding to treatment, PERGs of the amblyopic eye were as large as, or larger than, those of the fellow eye. The loss is greater with smaller checks. Retinal changes do occur after age 4 but so slowly that responses in heavily occluded eyes are not reduced. An additional level in the visual pathway is thus accessible to evoked potential investigation.

Amblyopia↗
PubMed1991

Topographical analysis of peripheral vs central retina with pattern reversal visual evoked response and the scanning laser ophthalmoscope.

The contribution of the central and the surrounding peripheral retina to the pattern reversal visual evoked response (PVER) was analyzed simultaneously using double frequency stimulation and the Fast Fourier transform (FFT) method. The Scanning Laser Ophthalmoscope (SLO) was used to project the pattern stimulus, a square subtending 10 degrees on a side, on a specific location in the fundus and to monitor accurately the stimulus' position during PVER testing. When the stimulus area on the central retina was less than or equal to 50 min of arc on a side, or 0.69% of the total area was stimulated (a square of 10 degrees on a side), the contribution from the central retina was negligible, and the PVER was dominated by surrounding peripheral retinal activity. When the stimulus area of the central retina was greater than or equal to 100 min of arc on a side, or 2.78% of the whole area was stimulated, activity from the central retina became more evident. When the stimulus area projected on the central retina became 150 min on a side (6.25% of the area or greater), activity from the central retina showed an increase and exceeded that of the peripheral retina. When the central area became larger, its activity dominated the PVER, and the contribution from the peripheral retina became negligible at this stage. The PVER was highly dependent upon the activity of the central retina, and activity levels from the central and surrounding peripheral retina were correlated.

Adult↗
PubMed1984

Spatial summation in subregions of simple-cell receptive fields in cat striate cortex as a function of slit length.

Spatial summation along the optimum stimulus orientation in subregions of simple-cell receptive fields in cat striate cortex was studied quantitatively by measuring the response to stationary light slits of variable length. Before summation analysis, the cell's discharge field was mapped by flashing a test slit on and off in a sequence of positions through the receptive field. A static activation procedure was used to determine the extension of subregions of the receptive field where light stimulation increased (enhancement) or decreased (suppression) the firing rate. An activation slit in the optimum orientation was positioned in the most responsive position of the discharge field and the effects of a parallel test slit, in a series of broadside positions, were assessed from the changes induced in the discharge elicited by the activation slit. Length-response curves for on and off responses were made by positioning a test slit in the respective subregions of the discharge field. The activation procedure was used to make length-response curves for suppression. A test slit of variable length was positioned in a suppression region defined by the activation profiles and an activation slit of fixed length was centred in the most responsive discharge field position. Length summation was found for all cells, both with respect to on and off responses, and suppression. The curves for on and off responses had a maximum value beyond which the response declined or levelled off, but some cells had a secondary, more shallow increase beyond an initial, steeply rising part. Similar properties were found for summation of suppression except that the effects were opposite in sign. Curves made for both on and off regions in the same cell often differed in shape. Such differences were also found when length-response curves made in different suppression regions of the same cell were compared. The various length-summation functions were explained by a model presuming that simple-cell receptive fields consist of partially overlapping non-concentric excitatory and inhibitory fields. This arrangement would also explain why length-response curves in various subregions often had different shapes.

Animals↗
PubMed1986

Electrophysiological assessment of aphakic cystoid macular oedema.

Focal electroretinograms (FERG), pattern electroretinograms (PERG), and visual evoked potentials (VEP) were studied in a group of 30 aphakic patients with cystoid macular oedema (ACME). When compared with a control group of age-matched aphakics, 35% of patients were found to have abnormal FERG responses and 53%--over half of whom had normal FERG responses--showed abnormal PERG amplitudes. Although most of the patients had associated optic disc leakage, VEP latencies were normal in 26 out of 30. These results may explain the more severe visual loss seen in some ACME patients where the ophthalmologically visible retinal changes do not seem sufficient to explain such reduction in vision.

Adult↗
PubMed1986

Visual evoked potential latency and contrast sensitivity in patients with posterior chamber intraocular lens implants.

An electrophysiological investigation of visual evoked potential (VEP) latency and contrast sensitivity was performed in a group of 13 patients who had undergone extracapsular cataract surgery with posterior chamber lens implantation. In spite of good postoperative visual acuity, abnormalities were detected in nine of the group (69%). This study suggests that, even with successfully implanted lenses, there may be a reduction in visual function which could be the result of altered transmission through the plastic lenticulus or fibrosis of the posterior lens capsule, and/or subtle changes in retinal architecture, not observed ophthalmoscopically.

Aged↗
PubMed1987

Visual function and pattern visual evoked response in optic neuritis.

The disparity between clinical visual function and pattern visual evoked response (VER) was studied in 53 patients who had suffered an attack of optic neuritis (ON) more than six months before. The visual functions tested included Snellen visual acuity, colour vision, visual field, and contrast sensitivity. The effect of pattern presentation, check size, and luminance was tested by recording VERs with several stimulus configurations. VER amplitudes were found to be associated with the outcome of all four clinical tests, independently of check size, luminance, or the presentation method used. On the other hand VER latencies were hardly ever related to the results of any of the four clinical visual tests. These findings support the idea that VER amplitude provides information about visual spatial perception, while VER latency is more related to the extent of demyelination.

Adolescent↗
PubMed1981

Pattern-onset visual evoked potentials in suspected multiple sclerosis.

Visual evoked potentials (VEPs) were obtained by monocular stimulation using a checkerboard pattern-reversal and pattern-onset technique. In 11 normal subjects, pattern-onset VEPs were generally larger, better defined, and less ambiguous than those elicited by pattern-reversal, because of the biphasic waveform characteristically obtained with pattern-onset stimulation. In 68 of 105 patients with possible multiple sclerosis, VEPs were normal in latency by both methods, and in nine adequate comparison was not possible. The incidence of normal VEPs to pattern-reversal was similar to that found in several other studies of patients with possible multiple sclerosis. Among the remaining 28 patients in whom VEP abnormalities were found, an increased latency was detected in 75% with the pattern-reversal technique, and in 96% by pattern-onset. In these patients, VEP abnormalities were obtained by monocular stimulation of each of 46 eyes, and among these the pattern-reversal technique yielded abnormalities in 59% and the pattern-onset method in 98%. These results indicate that VEPs elicited by pattern-onset are useful in investigating patients with suspected multiple sclerosis, and the diagnostic yield may be greater than with conventional pattern-reversal techniques.

Adult↗
PubMed1984

VEP changes in Parkinson's disease are stimulus dependent.

Two stimulus configurations (gratings and checkerboards) have been presented to a series of consecutive patients with the aim of exploring VEP changes in Parkinson's disease. The outcome turned out to be quite different according to the stimulus employed. Specifically, grating pattern produced a high diagnostic yield as opposite to checkerboard, which did not reveal substantial modifications of the latency of the VEP major positive peak with respect to a control group. This finding raises problems as to the characteristics of visual changes associated with Parkinson's disease.

Aged↗
PubMed1984

Reproducibility of the visual evoked potential using a light-emitting diode stimulator.

The intersubject and intrasubject reproducibility of the VEP was evaluated using two different methods of producing pattern reversal--a mirror/projector system and a light-emitting diode (LED) system. Intersubject reproducibility was determined in 100 normal subjects (50 males, 50 females). Ten subjects were studied on ten different occasions over 11 months to establish intrasubject reproducibility. The two methods gave comparable results. It is concluded that the mirror/projector system has no advantages over the LED system, which is cheaper, more robust and more convenient. Most of the intersubject variability was found to be due to subject variables and it is concluded that technical improvements are unlikely to reduce further the variability of the test. A variability in the latency of P100 of up to 7.7 ms was recorded in the serial studies on the ten subjects, indicating that in longitudinal studies on patients, changes in latency must exceed 9-10 ms to be significant. With both stimulus systems, there were significant sex-related differences in latency (P50 and P100 but not N70) and amplitude (N70-P100). The extent of the difference was such that the upper limit of normal latency for P100 (2.5-3 SD from the mean) was 4.2-4.7 ms longer for males than females-a value which exceeds 1 SD. Separate control values for males and females are advisable whichever method is used to produce pattern reversal.

Adolescent↗
PubMed2005

Differences in onset latency of macaque inferotemporal neural responses to primate and non-primate faces.

Neurons in the visual system respond to different visual stimuli with different onset latencies. However, it has remained unknown which stimulus features, aside from stimulus contrast, determine the onset latencies of responses. To examine the possibility that response onset latencies carry information about complex object images, we recorded single-cell responses in the inferior temporal cortex of alert monkeys, while they viewed >1,000 object stimuli. Many cells responded to human and non-primate animal faces with comparable magnitudes but responded significantly more quickly to human faces than to non-primate animal faces. Differences in onset latency may be used to increase the coding capacity or enhance or suppress information about particular object groups by time-dependent modulation.

Animals↗