Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “AFTERIMAGE”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

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

At least 235 records · Page 13Linked to original sources
PubMed1985

The flight of colors test in multiple sclerosis.

Flight of colors (FOC), the rapidly changing series of colored afterimages perceived when a bright light briefly strikes the eye, is impaired or absent in patients with lesions affecting central visual fields, especially optic neuropathies (ONs). The effectiveness of a bedside test of FOC using a pocket flashlight was compared with that of pattern-reversal visual evoked responses (PRVERs) in examining 74 subjects): 20 controls, seven patients with ON not due to multiple sclerosis (MS), 26 patients with MS, and 21 patients with possible MS and no clinical ON. The FOC test correctly identified 95 of 99 normal eyes and 45 of 49 eyes with ON, and accurately diagnosed 140 (95%) of 148 eyes overall. In 84 eyes examined by PRVER and FOC, the results agreed in 73 cases (87%), including those of subclinical ON.

Adult↗
PubMed1999

Vertical fusional vergence: the key to dissociated vertical deviation.

OBJECTIVES: To test the previous findings of Enright that disparity-induced vertical vergence is mediated primarily by the oblique muscles, and to relate this normal eye movement pattern to the eye movement pattern seen in subjects with dissociated vertical deviation. METHODS: Sixteen normal volunteers underwent 55 measurements of the cycloversion associated with prism-induced vertical vergence using an afterimage apparatus. A Vernier scale measured the direction and magnitude of the torsional shift that occurred with recovery of fusion on removal of a 3- or 4-prism diopter prism. RESULTS: Of the 55 trials, the directions of torsional shift were consistent with the oblique muscles being the primary mediators of vertical fusional vergence in 51 (93%) (P = .03 using a binomial distribution). The mean +/- SD value of torsional shift was 1.15 degrees+/-0.76 degrees in the expected direction. CONCLUSIONS: Vertical fusional vergences in this study were produced primarily by the oblique extraocular muscles. The eye movement patterns of these vertical vergences in normal subjects are qualitatively similar to those seen in recordings of patients with dissociated vertical deviation. Dissociated vertical deviation thus seems to be an exaggeration of a normally occurring eye movement pattern. The cyclovertical component of dissociated vertical deviation may help stabilize the fixing eye by damping vertical nystagmus, while the accompanying hypertropia is an incidental and undesirable side effect.

Adolescent↗
PubMed2000

Laser pointers and the human eye: a clinicopathologic study.

We report the absence of photic retinal injury after exposing the retina to light from class 3A laser pointers for durations of up to 15 minutes. Three patients with uveal melanomas were scheduled to have an enucleation. Each agreed to have his or her retina exposed to laser light from a class 3A laser pointer prior to enucleation. Continuous exposure was directed to the fovea for 1 minute, to the retina 5 degrees below fixation for 5 minutes, and to the retina 5 degrees above fixation for 15 minutes. Ophthalmoscopic evaluation of the cornea, lens, and retina and fluorescein angiographic studies of the retina were conducted before, 24 hours after, and 11 days after laser exposure in the first case; before and 86 hours after exposure in the second case; and before, 96 hours after, and 15 days after exposure in the third case. Other than transient afterimages that lasted only a few minutes, we were unable to document any functional, ophthalmoscopic, fluorescein angiographic, or histologic evidence of damage to any structures of the eyes. Transmission electron microscopic studies of retinal sites targeted by the laser pointers in the second and third cases revealed ultrastructural abnormalities in the outer retina and the pigment epithelium that were similar to abnormalities seen in the retina approximately 8 mm away from the targeted sites. The risk to the human eye from transient exposure to light from commercially available class 3A laser pointers having powers of 1, 2, and 5 mW seems negligible.

Adult↗
PubMed1995

Visual disturbance secondary to clomiphene citrate.

OBJECTIVE: To identify a distinctive constellation of persistent visual abnormalities secondary to treatment with clomiphene citrate. DESIGN: Description of the clinical findings in three patients with visual disturbance secondary to clomiphene treatment. SETTING: A neuro-ophthalmology referral center. PATIENTS: Three women aged 32 to 36 years treated for infertility with clomiphene for 4 to 15 months. RESULTS: All three patients experienced prolonged afterimages (palinopsia), shimmering of the peripheral field, and photophobia while undergoing treatment with clomiphene. The results of the neuro-ophthalmologic examination and electrophysiologic studies were normal in all three patients. Unlike previously reported cases, visual symptoms did not resolve on cessation of treatment. Patients remain symptomatic from 2 to 7 years after discontinuing treatment with the medication. CONCLUSIONS: Treatment with clomiphene can cause prolonged visual disturbance. Patients who develop such symptoms should be advised that continued administration may cause irreversible changes. Women with characteristic visual symptoms should be questioned about past use of clomiphene.

Adult↗
PubMed1996

Persistent palinopsia following ingestion of lysergic acid diethylamide (LSD).

OBJECTIVE: To identify a distinctive chronic visual complication of lysergic acid diethylamide (LSD) use. DESIGN: Description of the clinical findings in three patients with this disorder. SETTING: A neuro-ophthalmology referral center. RESULTS: All three patients experienced prolonged afterimages (palinopsia) during LSD intoxication and have continued to be symptomatic up to 3 years after they ceased to ingest the drug. Results of neuro-ophthalmologic and neurologic examinations and neuroimaging and electrophysiologic studies were normal. CONCLUSIONS: We have described three patients in whom persistent palinopsia developed following ingestion of LSD. Clinicians should inquire about past LSD use in all patients who initially have seemingly spontaneous, isolated palinopsia. Recognition of this distinctive clinical syndrome associated with LSD use might avoid unnecessary anxiety and excessive diagnostic tests for patients with this disorder.

Adolescent↗
PubMedDate not supplied

Pavlovian conditioning with proximal stimuli.

This experiment was conducted with the objective of demonstrating that the effective stimuli in Pavlovian Conditioning are not environmental stimuli but internal physiological processes elicited by environmental input (proximal stimuli). In order to achieve the objective, afterimages in color vision were used: looking at a diffuse lightened circle after seeing a red circle yields an image of a green circle. A differential conditioning paradigm with two sequential compounds was run. In one group (G+B-: n1 = 10), a red circle followed by a green circle was paired with shock, whereas a red circle followed by a blue circle remained unpaired. A second group (G-B+: n2 = 10) received red-blue paired trials and unpaired red-green trials. Immediately after that training, subjects were tested with a new, never trained sequential compound: a red circle followed by a diffuse lightened circle. Furthermore, they were tested with the already trained compounds. Taking the environmental point of view, the never trained stimulus should elicit an orienting response lying in between the excitatory reaction to the paired stimulus and the inhibitory reaction to the unpaired stimulus. From the proximal point of view, the diffuse light should elicit an excitatory reaction in group G+B- and an inhibitory reaction in group G-B+. Electrodermal conditioned anticipatory and omission responses were measured. The results supported the proximal hypothesis. Hence, defining input in environmental terms may be the wrong way. Instead, in conceptualizing the stimulus in conditioning, the following should be considered: the processing organism itself is creating the effective stimuli.

Adult↗
PubMed1975

Visual parameters associated with recovered retrobulbar optic neuritis.

Visual acuity, color vision, pupillary reaction, induced Pulfrich phenomenon, kinetic fields, static fields, afterimage testing, and ophthalmoscopic evaluation were studied in nine patients with a history of retrobulbar neuritis. The most consistently reliable test for determining the presence of an old optic nerve defect in these patients was meridional 0 to 180 degrees static perimetry. There was a uniform decrease in brightness discrimination to either side of the foveal peak.

Accommodation, Ocular↗
PubMed1984

The effect of testing method on stereoanomaly.

Previous tests of stereoanomaly (a deficit in stereopsis for a given disparity direction, crossed or uncrossed) have employed stimuli in which physical contours are presented with large disparities at exposure durations too brief for eye movements. This study investigated stereoanomaly using alternative testing methods with two types of stimuli: (1) stereoscopic contours formed from dynamic random-element stereograms presented both briefly and continuously, and (2) afterimages of retinally disparate physical contours. The results from three experiments show that most subjects who are classified as stereoanomalous under conditions of brief exposure perform normally under conditions that allow long inspection periods while eliminating eye movements. These results suggest that anomalies in stereopsis previously reported may depend on the method of testing rather than on deficits in underlying neural mechanisms.

Afterimage↗
PubMed1984

Characteristics of smooth eye movements with stabilized targets.

Eye movements of two subjects were recorded with a Double Purkinje Image Tracker while they pursued horizontal triangle or ramp stimuli (1, 2, 4 or 8 degrees/sec, p--p 8 degrees). Subjects then attempted to imitate their smooth pursuit eye movement patterns with an electronically-stabilized target or with an afterimage. Next, they attempted to reset the velocity of the stimulus to their memory of the velocity they had previously pursued. The smooth pursuit eye movements of both subjects were very similar. Their attempts to imitate this pattern of eye movements with a stabilized target were only partially successful and subject to large, qualitative individual differences. These differences did not arise from faulty memories of the nature of the pursuit stimuli. Similar results were obtained on the vertical meridian, with a lighted background, and with the stabilized target in eccentric retinal positions. We conclude that stabilization techniques are of dubious value in elucidating properties of the human smooth pursuit subsystem.

Afterimage↗
PubMed1985

Visual cortical correlates of visible persistence.

In order to evaluate their possible role in visible persistence, cortical cells from area 17 of the cat were investigated with a stationary light bar flashed for different durations. Thirteen out of 72 cells with non-overlapping On and Off subregions were able to respond to the briefest On stimulus (12.5 msec) for low and moderate contrasts. The responses of these cells outlasted brief On stimuli and this neural persistence increased as the On duration was shortened, mimicking the inverse duration effect of visible persistence. The 30 cells with overlapping On and Off subregions were all able to respond to brief stimuli but their neural persistence was independent of stimulus duration. At very high contrast levels, the inverse duration effect, observed in cells with non-overlapping subregions, disappeared since the On responses were followed by Off rebound discharges regardless of stimulus duration. It is suggested that the latter responses are a possible cortical equivalent of positive afterimages.

Afterimage↗
PubMed1989

Spatial organization of sensitivity regulation in rod vision.

To investigate whether scotopic sensitivity is set locally or in neural "pools", we have tested the spatial variation in sensitivity after bleaching with gratings using 3 different methods. One experiment circumvented the influence of involuntary eye movements by deliberately randomizing the horizontal position of a fine test line on the area bleached by the vertical gratings. The spatial variation of threshold across the bleached area is reflected in the width of the frequency-of-seeing curve. A clear difference between the probability-of-seeing curves following a grating bleach and a uniform bleach was seen only up to between 4.2 and 6.3 c/deg, suggesting that adaptation signals are pooled so as to almost obliterate the contrast in finer gratings than this. In a second experiment the lowest bleaching-grating contrast (for a space-averaged initial rhodopsin bleach of 10%) that produced a patterned afterimage stayed close to the scotopic threshold contrast for frequencies from 1 to 6.4 c/deg, but it rose above the contrast threshold at high spatial frequencies. This slight loss of sensitivity at the high frequencies is more evidence for pooling in adaptation. A third experiment assessed the sensitivity profile at the adapting site without any influence of later stages of neural integration. Bleaching and test gratings of slightly different spatial frequency were flashed successively. If the effect of bleaching is restricted to the bleached rods, the observer will effectively be looking at the test grating through a grid of sensitive and insensitive stripes in his own retina. The two gratings come in and out of register at the difference frequency, and a corresponding low-frequency grating should be visible even when the test and bleaching gratings are not themselves resolved by the later stages. We could not see the difference frequency unless the test and bleach gratings were themselves coarse enough to be resolvable in rod vision. This is very strong evidence against any model in which each rod has its own sensitivity-regulating mechanism, and instead supports (for these conditions) Rushton's view that adaptation is entirely the work of a neural pool. The estimated pool size is about 10 min arc of visual angle.

Adaptation, Ocular↗
PubMed1993

Depth in anticorrelated stereograms: effects of spatial density and interocular delay.

Disparity-based depth is not perceived in densely textured, anticorrelated random-dot stereograms (RDSs) whose elements carry opposite signs of brightness contrast on corresponding loci, as extant data show. We observed global depth in anticorrelated RDSs flashed repetitively with an interocular delay. During the delay time, a dot array in one eye was paired with a gray frame in the other eye and thus could interact with the negative afterimage of the contralateral dot array. A correlated RDS (e.g. 8 min arc dots, 50% density, 15-msec flash duration) lost depth with delays > 45 msec. An anticorrelated RDS, that was otherwise identical, showed robust depth when flashed with an interocular delay of some 60 msec. A delay was not always necessary to produce depth. At low dot density (1-2%), anticorrelated RDSs showed disparity-dependent local depth even when displayed continuously, or flashed simultaneously; as dot density alone was increased, depth was progressively lost. To make global depth visible in a dense RDS flashed with an interocular delay, the internal response had to be strongly biphasic. Our results support the generally held notion that cyclopean depth signals emerge exclusively from same-sign binocular cortical filters. However, the exclusionary rule may be invalid with respect to the processing of coarse local depth with figural stimuli. Relative depth between a pair of small dots was easily perceived when one of the dots was in opposite contrast, but the depth threshold was then about 0.5 log unit higher than with the same-contrast pair of dots indicating that the internal effects of contrast have not all lost their sign prior to binocular disparity processing. It remains to be determined whether depth can be perceived from edges of opposite contrast.

Afterimage↗
PubMed2004

The aperture problem in egocentric motion.

When only a featureless straight contour of a moving object is visible, one cannot tell its true velocity and the object seems to be moving perpendicularly to its orientation. Using psychophysics and brain imaging, Goltz et al. have now demonstrated that this aperture problem also occurs in visual representations in egocentric coordinates. An afterimage of inclined lines that is perceived to move with smooth-pursuit eye movements appears to move perpendicularly to the lines rather than in the tracking direction.

Afterimage↗
PubMed2005

Illusory motion induced by the offset of stationary luminance-defined gradients.

An illusory motion induced by the offset of a stationary gradient stimulus is characterized. When a gradient stimulus, whose luminance contrast ranges gradually from white on one side to black on the other, is made to disappear all at once so that only the uniform white background remains visible, illusory motion is perceived. This motion lasts approximately 700 ms, as if the stimulus moves from the low to the high luminance contrast side. This gradient-offset induced motion does not occur for equiluminant color-defined gradient offsets, suggesting that it relies mainly on the magnocellular pathway. Our data are consistent with the hypothesis that this illusion is caused by the decay of the gradient afterimage.

Afterimage↗
PubMed2001

Are corresponding points fixed?

Several investigators have claimed that the retinal coordinates of corresponding points shift with vergence eye movements. Two kinds of shifts have been reported. First, global shifts that increase with retinal eccentricity; such shifts would cause a flattening of the horopter at all viewing distances and would facilitate fusion of flat surfaces. Second, local shifts that are centered on the fovea; such shifts would cause a dimple in the horopter near fixation and would facilitate fusion of points fixated at extreme viewing distances. Nearly all of the empirical evidence supporting shifts of corresponding points comes from horopter measurements and from comparisons of subjective and objective fixation disparity. In both cases, the experimenter must infer the retinal coordinates of corresponding points from external measurements. We describe four factors that could affect this inference: (1) changes in the projection from object to image points that accompany eye rotation and accommodation, (2) fixation errors during the experimental measurements, (3) non-uniform retinal stretching, and (4) changes in the perceived direction of a monocular point when presented adjacent to a binocular point. We conducted two experiments that eliminated or compensated for these potential errors. In the first experiment, observers aligned dichoptic test lines using an apparatus and procedure that eliminated all but the third error. In the second experiment, observers judged the alignment of dichoptic afterimages, and this technique eliminates all the errors. The results from both experiments show that the retinal coordinates of corresponding points do not change with vergence eye movements. We conclude that corresponding points are in fixed retinal positions for observers with normal retinal correspondence.

Accommodation, Ocular↗
PubMed2001

Filling-in of the foveal blue scotoma.

The blue-blindness (tritanopia) of the human foveola normally goes unnoticed but can be directly visualized by having observers view a flickering, monochromatic, short-wavelength field. The blue scotoma appears as a tiny dark spot in central vision, the visibility of which depends upon the wavelength of the field and the temporal frequency of modulation. Comparisons of fading times as a function of flicker frequency for the blue scotoma, foveal afterimages and optically stabilized images indicate a common time course, consistent with the hypothesis that perceptual filling-in of the foveal blue scotoma reflects the operation of neural processes similar to those involved in fading and regeneration of stabilized images.

Afterimage↗
PubMedDate not supplied

Visual aftereffects and the consequences of visual system lesions on their perception in the rhesus monkey.

This study examined the consequences of visual system lesions on visual aftereffects produced by achromatic stimuli of various luminance contrasts and chromatic stimuli of various wavelength compositions. The effects of repeated exposure to such adapting stimuli were assessed using probes whose luminance contrast and wavelength composition were systematically varied using both detection and discrimination paradigms. Interocular tests revealed that both peripheral and central mechanisms contribute to the visual aftereffects produced by the adapting stimulus arrays used in this study. Contrary to the hypothesis according to which the midget system of the retina is the conveyor of visual afterimages, we found that blocking this system with lesions of parvocellular lateral geniculate nucleus, through which the midget cells make their way to the striate cortex in primates, did not eliminate the visual aftereffects. It appears therefore that the parasol system of the retina, which courses through the magnocellular layers of the lateral geniculate nucleus to cortex, can convey the necessary signals for the generation of visual aftereffects. Lesions of areas V4 and MT did not have significant effects on the visual aftereffects studied suggesting that the central factors that contribute to the visual aftereffects occur either already in area V1 or are conveyed to higher centers through regions other than areas V4 and MT.

Adaptation, Ocular↗
PubMed1998

Retinotopy and color sensitivity in human visual cortical area V8.

Prior studies suggest the presence of a color-selective area in the inferior occipital-temporal region of human visual cortex. It has been proposed that this human area is homologous to macaque area V4, which is arguably color selective, but this has never been tested directly. To test this model, we compared the location of the human color-selective region to the retinotopic area boundaries in the same subjects, using functional magnetic resonance imaging (fMRI), cortical flattening and retinotopic mapping techniques. The human color-selective region did not match the location of area V4 (neither its dorsal nor ventral subdivisions), as extrapolated from macaque maps. Instead this region coincides with a new retinotopic area that we call 'V8', which includes a distinct representation of the fovea and both upper and lower visual fields. We also tested the response to stimuli that produce color afterimages and found that these stimuli, like real colors, caused preferential activation of V8 but not V4.

Afterimage↗