PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “AFTERIMAGE”

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 19 recordsLinked to original sources
PubMed1995

Visual scotoma and visual afterimages: some evidence that the perceived visual afterimage may not be a purely retinal phenomenon: a single case study.

Observations of the differential appearance and behaviour of a deliberately induced visual scotoma and a patterned visual afterimage are reported. Although a retinal scotoma behaves like a visual afterimage in some ways, there are sufficient differences to suggest that the perceived visual afterimage may not be just the simple consequence of prolonged retinal stimulation.

Afterimage↗
PubMed1986

Afterimage-like effects in the motion-sensitive neuron H1.

A powerful effect resembling an afterimage is demonstrated on the pathway to the motion-sensitive neuron H1. This effect is independent of the locally generated gain control described in an earlier paper (Maddess & Laughlin 1985, Proc. R. Soc. Lond. B 225, 251). The afterimage, produced across the eye by a stationary pattern, causes the sensitivity to movement to be different according to the local stimulus history, and the effects of low-contrast (0.1) patterns, presented for as little as a few hundred milliseconds, remain for up to 2 s. Moving patterns interact with the afterimage to modulate the spike rate of H1. The afterimage increases with contrast but saturates at contrasts above 0.5. Low spatial frequencies generate afterimages less effectively than moderate ones; this result indicates that the afterimage process could lie at, or after, lateral inhibition between tonic units. This is supported by the fact that the altered sensitivity profiles generated by single bright and dark vertical bars initially resemble Mach bands. However, this character alters as the afterimage decays, and the depression of H1's response to moving bright stimuli, produced by the afterimage of a dark bar, continues to grow for up to 1 s after the adapting bar is removed. A short-lived (0.5 s) reduction of H1's directional selectivity accompanies strong afterimage formation. All these factors, especially the saturation at low contrasts and the spatial frequency tuning, rule out light adaptation by photoreceptors as the afterimage source. Luminances used were also low enough to exclude influence by the pupil mechanism. Lastly, responses to patterns that are occasionally jumped by large or small distances are broadened by stimuli that produce an afterimage. Responses to small displacements have previously been described as 'velocity impulse responses' (Srinivasan 1983, Vision Res. 23, 659; Zaagman et al. 1983, IEEE Trans. SMC 13, 900) and so the response broadening (stimulus blurring) can be taken as a reduction of the fly's temporal resolution of moving objects. Previously reported work shows that afterimages seen in humans and the effect reported here act over the same range of temporal frequencies rather than retinal drift speeds. This may suggest an important role for afterimage-like effects in the processing of the low temporal frequency components of moving images. Certainly, the fly's afterimage system reduces the visibility of moving objects within patches of an image that, have on average, contained slowly varying motion signals.(ABSTRACT TRUNCATED AT 400 WORDS)

Afterimage↗
PubMed1986

Negative afterimages and photopic luminance adaptation in human vision.

Previous studies of the negative afterimage have reported that the process responsible for these aftereffects has a bandpass spatial characteristic. If this finding is correct, then negative afterimages cannot arise from a simple, local, adaptive process. I remeasure the spatial-frequency characteristic of the negative-afterimage process by using an afterimage contrast-matching procedure with retinally stabilized stimuli and find the spatial characteristic to be constant in the low-spatial-frequency region. This finding is consistent with the theory that the negative afterimage results from local luminance adaptation. As a test of the local adaptation explanation of the negative afterimage, the effect of the negative afterimage on the temporal contrast-sensitivity function (CSF) (measured down to 0.062 Hz) is determined. The apparent contrasts of the negative afterimages associated with very slowly (less than 0.5 Hz) flickering, threshold-contrast stimuli are calculated from power-function descriptions of the temporal development of the negative afterimage, and these afterimage contrasts are then subtracted from the temporal CSF's. The resulting curves are constant for temporal frequencies below 1 Hz, indicating that the decline in sensitivity at lower temporal frequencies is due entirely to the negative-afterimage process. Both the spatial and the temporal characteristics of the negative-afterimage process are consistent with its being a component of local luminance adaptation.

Acclimatization↗
PubMed2001

Afterimage of perceptually filled-in surface.

An afterimage induced by prior adaptation to a visual stimulus is believed to be due to bleaching of photochemical pigments or neural adaptation in the retina. We report a type of afterimage that appears to require cortical adaptation. Fixating a neon-color spreading configuration led not only to negative afterimages corresponding to the inducers (local afterimages), but also to one corresponding to the perceptually filled-in surface during adaptation (global afterimage). These afterimages were mutually exclusive, undergoing monocular rivalry. The strength of the global afterimage correlated to a greater extent with perceptual filling-in during adaptation than with the strength of the local afterimages. Thus, global afterimages are not merely by-products of local afterimages, but involve adaptation at a cortical representation of surface.

Adaptation, Ocular↗
PubMed1993

Measurements of chromatic and achromatic afterimages.

Several types of measurement were made of the negative afterimages formed by viewing chromatic and achromatic sine-wave conditioning gratings that were stabilized on the retina. We varied the spatial frequency, contrast, and duration of the conditioning stimulus and the interval between its offset and the afterimage measurement. Different methods of measuring afterimage contrast were also compared. We conclude that (1) an isoluminant chromatic stimulus creates an isoluminant chromatic afterimage; (2) afterimage contrast is linearly related to conditioning contrast; (3) chromatic and achromatic afterimages have similar low-pass spatial-frequency characteristics; (4) both types of afterimage build up and decay exponentially, with a (1/e) time constant of 4-8 s; (5) most important, both chromatic and achromatic afterimages raise the threshold for a chromatic flashed grating, but neither affects the threshold for an achromatic flashed grating; (6) we can explain these results by postulating that negative afterimages are subserved only by the sustained, or parvocellular, pathways.

Afterimage↗
PubMed2003

Attention during adaptation weakens negative afterimages.

The effect of attention during adaptation on subsequent negative afterimages was examined. One of 2 overlapped outline figures was attended during a 7-10-s adaptation period. When the figures were readily perceptually segregated (on the basis of color or motion), the subsequent afterimages were initially weaker for the previously attended figure. This effect was confirmed by demonstrations that the onset of a single afterimage was delayed when an afterimage inducer was attended during adaptation compared with when a central digit stream or an overlapped (brightness-balanced) figure that did not generate an afterimage was attended. The attention effect was further confirmed using a criterion-independent (dot-integration) paradigm. The fact that selective attention during adaptation weakened or delayed afterimages suggests that attention primarily facilitates the adaptation of polarity-independent processes that modulate the visibility of afterimages rather than facilitating the adaptation of polarity-selective processes that mediate the formation of afterimages.

Adaptation, Psychological↗
PubMed1984

Pattern and orientation effects on afterimage duration.

Patterns composed of a pair of lines: vertical + horizontal, vertical + oblique, horizontal + oblique, and oblique + oblique, either centrally-aligned or edge-aligned, were shown at two positions of rotation. After a 1-s exposure to the pattern observers timed the duration of afterimages consisting of individual lines (fragmentary state) and the pattern as a whole (unitary state) for the ensuring 60 s. Summing unitary and fragmentary afterimage durations yielded the total afterimage duration for each pattern. Three hypotheses were confirmed by the results: (i) total afterimage duration is constant for all patterns when integrated spatiotemporal luminances are equal; (ii) unitary afterimage duration is also constant; (iii) fragmentary afterimages of vertically oriented lines have longer durations than either their horizontal or oblique pair members, regardless of alignment and, with one exception, rotation. For all patterns, the durations of the unitary and the fragmentary state represent a fixed portion of the total afterimage duration. The difference between afterimage duration for differently oriented lines in patterns which include a vertical is discussed in relation to the vertical-horizontal illusion, the function and structure of cortical orientation processes, and perceptual development.

Adult↗
PubMed1982

Role of threshold in afterimage visibility.

The negative afterimage from grating can be considered equivalent to a renal grating, the contrast of which decreases over time. The interval between the onset of the afterimage and the time at which the effective contrast of the afterimage falls below threshold defines afterimage duration. In a series of experiments with several predictions based on this formulation were confirmed. Square-wave gratings yielded longer afterimage durations than sinusoidal gratings, a difference that is attributable to the difference in threshold between these two types of grating. Also, grating adaptation before afterimage induction was found to abbreviate afterimage duration because of threshold elevation. Finally, it was found that, even after fading to invisibility, an afterimage could interact with a real grafting to influence threshold performance on a forced-choice detection task.

Afterimage↗
PubMed1987

Afterimage movement during saccades in the dark.

The spatial values of retinal coordinates are "recalibrated" to the "egocentric" coordinates during and after a saccade within a fraction of a second. We measured the time constant of this retinal coordinate transformation by means of an afterimage technique: our ten subjects performed "auditory" horizontal saccades in total darkness (0.2-4.5 saccades/sec). At a saccade frequency below 1 saccade/sec, the subjects observed saccadic displacement of the foveal afterimage, but the afterimage seemed to arrive at its final position more slowly than the center of gaze (state 1). At saccade frequencies above 1.5 saccades/sec, the perceived amplitude of afterimage displacement decreased with increased saccade frequency (state 2). Above 2 saccades/sec all subjects perceived two stationary afterimages simultaneously at the saccadic end-position (state 3). A further increase in saccade frequency reduced the distance between the two afterimages till only one stationary afterimage was seen in a mid-position between the two auditory targets at a saccade frequency above 3.2-3.5 saccades/sec (state 4). Saccade amplitude remained constant within the frequency range between 0.2 and 4.5 saccades/sec. A one-step or two-step linear model was applied to simulate the experimental data, indicating that the spatial coordinates shift more slowly than the saccadic eye movements.

Acoustic Stimulation↗
PubMed1986

Afterimage color perception for designers.

This is a study of perception of negative afterimages. Surface color samples were viewed under Spectralight. Subjects fixated on 11 Munsell hues mounted on white cards and matched their afterimages with chips from the Munsell Book of Color. Samples were drawn from 125 participants in two groups, one practiced, the other unfamiliar with afterimage. No single afterimage or Munsell color chip was reported for any of the stimulus hues. However, most afterimage responses for nine stimulus colors fell within one Munsell hue family. Afterimages reported for the remaining two stimulus colors of purple-blue and yellow-red span two adjacent hue families. Results suggest new alternatives to traditional subtractive color complements. New afterimage opposites are provided.

Adolescent↗
PubMed1992

Individual differences in afterimage persistence: relationships to hypnotic susceptibility and visuospatial skills.

To investigate the moderating role of individual differences in hypnotic susceptibility and visuospatial skills on afterimage persistence, we presented a codable (cross) flash of light to 40 men and 46 women who had been dark adapted for 20 min. In an unrelated classroom setting, subjects had previously been given two standardized scales of hypnotic susceptibility (Harvard Group Scale of Hypnotic Susceptibility, Shor & Orne, 1962; Group Stanford Hypnotic Susceptibility Scale, Form C, Crawford & Allen, 1982) and the Mental Rotations Test (Vandenberg & Kuse, 1978). The first afterimage interval and the afterimage duration correlated significantly with hypnotic responsiveness, supporting Wallace (1979), but did not show the anticipated relationships with mental rotation visuospatial skills. Individuals in the high hypnotizable group had (a) significantly longer afterimage intervals between its first appearance and first disappearance than did those in medium or low groups, as well as (b) significantly longer afterimages between the first appearance and the final disappearance than did those in low groups, but those in medium groups did not differ significantly from the other groups. Discriminant analysis using the afterimage persistence measures classified correctly 65.2% of high hypnotizables, 37.5% of medium hypnotizables, and 54.8% of low hypnotizables. Hypothesized cognitive skills that assist in the maintenance of afterimages and underlie hypnotic susceptibility include abilities to maintain focused attention and resist distractions over time and to maintain vivid visual images.

Adult↗
PubMed2000

Perceived motion in complementary afterimages: verification of a neural network theory.

Steady fixation of a regular pattern like a bar grating or concentric circles leads to a complementary afterimage at pattern offset. The afterimage has the appearance of shimmering lines that are locally orthogonal to the orientations of the inducing image. Additionally, the afterimage includes motion running parallel to the orientation of the afterimage lines. We argue that this afterimage motion supports the existence of a cue to motion that is based on the spatial organization of oriented responses. This cue was previously proposed after analysis of a neural network model of visual perception. We test predictions of the model on various types of complementary afterimage inducing stimuli. When a contrast or size gradient is included in the inducing image, the afterimage motion moves toward the higher part of the gradient, in agreement with the model. Implications of this cue for computational and neurophysiological theories of motion perception are discussed.

Figural Aftereffect↗
PubMed1985

Afterimages of sinusoidal, square-wave and compound gratings.

Negative afterimages were observed after steady fixation of sinusoidal gratings at low spatial frequencies, and quantified using contrast-matching and cancellation methods. Afterimage contrast increased as a power function of "exposure", defined as the product of inspection contrast and inspection duration. A single function, linear on a log-log plot, describes the afterimages of gratings at different spatial frequencies, contrasts and durations. The matching method yielded a lower slope (about 0.42) than the cancellation method (0.62), probably because contrast adaptation attenuates perceived afterimage contrast in the first method, but not the second. Square-wave gratings, and those containing two or three harmonic components gave much weaker afterimages (assessed by contrast-matching) than sine-waves did. Contrast adaptation may again be responsible. Hemi-field asymmetries in contrast perception were noted. The contrast of real gratings and afterimages was nearly additive, especially at lower exposures, but the results cannot distinguish between linear filter and gain control models of "local adaptation".

Adaptation, Ocular↗
PubMed1999

Afterimages: a tool for defining the neural correlate of visual consciousness.

Our visual system not only mediates information about the visual environment but is capable of generating pictures of nonexistent worlds: afterimages, illusions, phosphenes, etc. We are "aware" of these pictures just as we are aware of the images of natural, physical objects. This raises the question: is the neural correlate of consciousness (NCC) of such images the same as that of images of physical objects? Images of natural objects have some properties in common with afterimages (e.g., stability of verticality) but there are also obvious differences (e.g., images maintain size constancy, whereas afterimages follow Emmert's Law: when seen while screens at different distances are observed, an afterimage looks larger, the greater the distance of the screen). The differences can be explained by differences in the retinal extent of images and afterimages, which favors the view that both have the same NCC. It seems reasonable to assume that before neural activity can produce awareness, all the computations necessary for a veridical representation of, e.g., an object, must be completed within the neural substrate and that information characteristic of a particular object must be available within the NCC. Given these assumptions, it can be shown that no retinotopic (in a strict sense) cortical areas can serve as the NCC, although some type of topographic representation is necessary. It seems also to be unlikely that neurons classified as cardinal cells alone can serve as NCC.

Afterimage↗