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PubMed1983

Afterimages, binocular rivalry, and the temporal properties of dominance and suppression.

When different contours are presented to the two eyes, an unstable percept, binocular rivalry, is the result. Parts of each set of contours may be seen but the two sets are not seen in the same place at the same time. The contours need not be physically present. Afterimages will produce binocular rivalry. Normal rivalry can be prevented if intermittent stimulation is used. Previous work has shown that orthogonal gratings, flashed for less than 150 ms and separated by more than 150 ms, will appear to fuse into a plaid or checkerboard pattern. In the present experiment this phenomenon is examined with afterimages used to produce rivalry. This abnormal 'fusion' is seen when negative afterimages are stroboscopically illuminated at less than 5 Hz. The results obtained with afterimages are predictable from the previous results obtained with stimuli external to the eye.

Adult↗
PubMed1992

The apparent shape of afterimages in the Ames room.

When observers project afterimages of circular patterns onto a surface slanting away from them the images are reported as being oval in shape. In this paper it is reported that this does not occur when similar afterimages are projected onto the slanting rear wall of an Ames room. Instead of appearing as ovals, the afterimages remain circular. It appears as though the actually-slanted rear wall of the room not only looks as if it is normal to the line of vision, but also that it functions as if it was in such an orientation as far as a projection surface for afterimages is concerned. While these results are consistent with Emmert's law and with traditional accounts of shape and size constancy, they raise once again the age-old issue of whether the 'image on the retina' constitutes an object of perception that can be described in terms of its shape or size.

Adult↗
PubMed2003

Interactions of afterimages for orientation and color: experimental data and model simulations.

Sequential viewing of two orthogonally related patterns produces an afterimage of the first pattern. We report an experiment that quantifies some properties of this type of afterimage. It is shown that it is important for the two patterns to have orthogonal orientations and that the appearance of the afterimage does not depend on the spatial frequency of the second pattern. We then show that Grossberg's model of interacting boundary and feature contour systems can account for the observed properties of these afterimages.

Color Perception↗
PubMed1989

Negative afterimages and the McCollough effect.

Four experiments were conducted to test earlier claims about the relationship between the negative afterimage and the McCollough effect. The first claim (Hansel & Mahmud, 1978) is that long-lasting afterimages occur when induced by the same alternating-stimulus procedure as that used to induce the McCollough effect. The second claim (Murch & Hirsch, 1972) is that afterimages can themselves induce McCollough effects if they are induced and paired sequentially with grating patterns. In testing these claims, a reliable computer-controlled color-cancellation technique developed earlier was used to measure the apparent color of both afterimages and McCollough effects objectively. No support was found for the first claim following alternative presentation of two homogeneously colored regions for total periods of 5 min (Experiment 1) and 20 min (Experiment 2). The second claim was fully supported: After an induction period of 7.3 min, a McCollough effect occurred for a red-vertical pairing but not for a green-horizontal pairing (Experiment 3); but after an induction period of 20 min, McCollough effects occurred strongly for both pairings (Experiment 4). The theoretical implications of these outcomes are considered in the context of recent theories of color and pattern processing in the visual system.

Adult↗
PubMed1988

Afterimages: a collective term for percepts of different origin.

Exposure of the eye to a strong photoflash results in a so-called "afterimage", which may last for 20 min or longer. In contrast, the true afterimage, which fluctuates in brightness and is best seen in complete darkness, lasts only a few minutes. This true afterimage can be attributed to the strong oscillatory neuronal responses immediately initiated by the flash. Thereafter dark and light regions, insensitivity percepts, are observable against bright and dark backgrounds, respectively. These percepts can be adequately explained by a reversal of the response behaviour of rod and cone driven ganglion cells situated along the contour of the flash-exposed area. The slow recovery of the rods explains why insensitivity percepts can be seen for many minutes.

Afterimage↗
PubMed1983

Positive and negative afterimages from brief target gratings.

Threshold luminance levels for the production of negative afterimages from brief target gratings were determined as a function of background luminance and grating frequency. The obtained thresholds were extremely low--typically below the values that would maintain constant space-average luminance between target and background. The implications of these results for other studies that may have inadvertently produced negative afterimages with their stimulus conditions were noted. As a demonstration, visual persistence estimates from these gratings were determined under conditions that carefully excluded negative afterimages, and clear differences from previously published work were obtained.

Afterimage↗
PubMed2004

Motion-induced blindness does not affect the formation of negative afterimages.

Aftereffects induced by invisible stimuli constitute a powerful tool to investigate what type of neural information processing can occur in the absence of visual awareness. This approach has been successfully used to demonstrate that awareness of oriented gratings or translating stimuli is not necessary to obtain a robust orientation-specific or motion-specific aftereffect. We exploit motion-induced blindness (MIB, Bonneh, Cooperman, & Sagi, 2001) to investigate the related question of the influence of visual awareness on the formation of negative afterimages. Our results show that MIB does not affect the persistence and intensity of afterimages. Thus, there is no significant contribution to the formation of afterimages beyond the sites mediating MIB.

Adult↗
PubMed1998

Nonlinear combination of luminance excursions during flicker, simultaneous contrast, afterimages and binocular fusion.

The changes in apparent brightness or color, induced into a test spot by a surround, can be greatly enhanced either by flickering the test spot between two luminances, or by binocularly fusing a pair of test spots of different luminances. Simultaneous contrast, in which a white surround makes a grey spot look darker, is greatly enhanced if the spot (not the surround) flickers between black and white. Colour contrast is likewise enhanced by chromatic flicker: on a blue surround, a grey spot looks slightly yellowish, but a yellow/blue flickering spot looks strongly yellow. Temporal successive contrasts, or negative afterimages, are also enhanced by flickering the test field. The negative afterimage of a half-white, half-black rectangle looked dark grey and light grey when projected on a grey test field, but it looked almost black and almost white when projected on a test field that flickered between black and white. Coloured negative afterimages were also enhanced by projecting them on a chromatic flickering test field. We examined the combination rules for pairs of luminances which were presented either successively as flicker or else dichoptically (and fused binocularly). The brightness averaging functions for spatial increments (light spots) on dark surrounds were quasi-linear for binocular fusion but quadratic for flicker. For spatial decrements (dark spots) on white surrounds, the brightness averaging functions were strongly nonlinear winner-take-all for both binocular fusion and flicker. We also found temporal analogues of Fechner's [(1860). Elements of psychophysics. New York: Holt, Rinehart, Winston, 1966] paradox and Levelt's [(1965). British Journal of Psychology, 56, 1-13] dichoptic contour effect. We conclude that the visual rules for combining luminance excursions, whether in flicker or binocular fusion, favour disproportionately the spot with the higher contrast.

Afterimage↗
PubMed1984

Disappearance of afterimages at 'impossible' locations in space.

An eccentrically positioned afterimage, viewed in the dark, will disappear if the eye is positioned so that the afterimage now projects to a more extreme location relative to straight ahead. It was found that the afterimage disappeared when it projected to a location which corresponded to the edge of the visual field defined by the brow, cheek, and nose. This suggests that visibility of stimuli from those retinal regions shadowed by the head is influenced by eye-position information.

Afterimage↗
PubMed1996

Cortical dynamics of boundary segmentation and reset: persistence, afterimages, and residual traces.

In previous work with a neural-network model of boundary segmentation and reset, the percept of persistence was linked to the duration of a boundary segmentation after stimulus offset. In particular, the model simulated the decrease of persistence duration with an increase in stimulus duration and luminance. Further evidence is revealed for the neural mechanisms involved in the theory. Simulations show that the model reset signals generate orientational afterimages, such as the MacKay effect, when the reset signals can be grouped by a subsequent boundary segmentation that generates illusory contours through them. Simulations also show that the same mechanisms explain properties of residual traces, which increase in duration with stimulus duration and luminance. The model hereby discloses previously unsuspected mechanistic links between data about persistence and afterimages, and helps to clarify the sometimes controversial issues surrounding distinctions between persistence, residual traces, and afterimages.

Afterimage↗
PubMed2006

The glare effect does not give rise to a longer-lasting afterimage.

The glare effect is an illusion in which a region appears self-luminous when flanked by gradients that decrease in luminance with distance from the region (Zavagno, 1999 Perception 28 835-838). This region also appears brighter than a surface of the same luminance. We investigated, using the paradigm of afterimages, whether a low-level mechanism at the level of the retina or LGN could account for this apparent brighter sensation. We first replicated the result from the literature that brighter and longer-lasting physical stimuli generate longer-lasting afterimages. We then compared the glare-effect stimuli with their counterpart controls, and found that the glare-effect stimuli did not give rise to longer-lasting afterimages. This suggests that the apparent brighter sensation of the glare effect is not due to a retinal or LGN mechanism, but must have a cortical origin.

Afterimage↗
PubMed1978

Autokinetic movement of an induced afterimage.

Thirty-two female Ss participated in an experiment in which autokinetic movement (AKM) direction change frequency of an induced afterimage was assessed as a function of stimulus afterimage color (yellow or blue-green) and the presence or absence of eye strain. Afterimage color was found not to affect AKM frequency reports. However, eye strain significantly (p less than .002) affected such reports, with the fewest AKM direction changes reported when strain was present. These results were explained in terms of an error signal and noise analysis of AKM.

Afterimage↗
PubMed1979

Initial-image and afterimage discrimination in the human rod and cone systems.

1. The rod-isolation technique of Aguilar & Stiles (1954) was used to obtain scotopic increment-threshold functions in the dark-adapted eye. Increment-threshold functions were obtained for background durations of 50 to 500 msec, but the onset of the background and increment fields was always simultaneous. In all conditions the duration of the increment field was 50 msec. 2. The pattern of results obtained is the same as that reported earlier for the cone system (Geisler, 1978). For background durations greater than that of the increment field, the increment-threshold functions have two distinct branches. It was shown, by measuring action spectra, that both branches reflect the sensitivity of the rod system. 3. When the increment thresholds are plotted as a function of background retinal illuminance, all the lower branches superimpose. This implies that those thresholds are dependent only on the number of background quanta absorbed during presentation of the increment field. On the other hand, when the increment thresholds are plotted as a function of background energy, all the upper branches superimpose, implying that those thresholds are determined by the total number of background quanta absorbed. 4. For the thresholds falling on the lower branches observes reported that the increment field was detected in the initital image of the background and increment fields when they were flashed. For the upper branches, the increment field was detected in a short-term afterimage that appeared after the background was extinguished. The higher the background intensity the longer was the latency until the increment appeared in the afterimage. 5. All of the above findings appear to be consistent with the known properties of the electrical responses of vertebrate photoreceptors. A model based on Penn & Hagins' (1972) model for the photocurrent in rat rods predicts, fairly accurately, the rod and cone increment-threshold results. The parameters estimated by fitting the model support the hypothesis that the short-term rod and cone afterimages are due to the relatively slow decay of internal transmitter, but they suggest that post-receptor mechanisms are responsible for the threshold saturation observed with flashed backgrounds.

Afterimage↗
PubMed1974

Rod origin of prolonged afterimages.

Afterimages fade against any unchanging background but generally reappear if the background changes suddenly. Under some conditions, however, a change of background color fails to revive a faded afterimage. This happens only if the interchanged backgrounds equally stimulate the rod receptors. It follows that afterimages seen under these conditions are generated by rods.

Afterimage↗
PubMed2005

Continuous flash suppression reduces negative afterimages.

Illusions that produce perceptual suppression despite constant retinal input are used to manipulate visual consciousness. Here we report on a powerful variant of existing techniques, continuous flash suppression. Distinct images flashed successively at approximately 10 Hz into one eye reliably suppress an image presented to the other eye. The duration of perceptual suppression is at least ten times greater than that produced by binocular rivalry. Using this tool we show that the strength of the negative afterimage of an adaptor was reduced by half when it was perceptually suppressed by input from the other eye. The more completely the adaptor was suppressed, the more strongly the afterimage intensity was reduced. Paradoxically, trial-to-trial visibility of the adaptor did not correlate with the degree of reduction. Our results imply that formation of afterimages involves neuronal structures that access input from both eyes but that do not correspond directly to the neuronal correlates of perceptual awareness.

Figural Aftereffect↗
PubMed1983

Apparent movement induced by afterimages.

A small light source viewed in the dark through an afterimage produced by an electronic flash may appear to move along short random paths. Experiment 1 shows that this is not an instance of the autokinetic phenomenon, and experiment 2 shows that it is not related to the 'fluttering hearts' phenomenon. On the basis of experiments 1 and 3 it is concluded that small-scale ocular drifts, microsaccades, and possibly tremors cause the whole afterimage to move. The afterimage serves as a frame of reference and induces movement of the light source.

Adolescent↗
PubMed2000

Emmert's law in the dark: active and passive proprioceptive effects on positive visual afterimages.

The relationship between apparent size and apparent distance is given by Emmert's law, which states that a retinal image is proportional in size to the distance of the surface it is projected upon. This principle also applies to retinal afterimages in that they, too, will change in apparent size if distance cues suggest that the location of the object onto the retinal image has been altered. It has also been known for some time that non-retinal cues can produce quantitative and qualitative effects on an afterimage when it is viewed in the dark. In the present two studies, positive afterimages of an observer's hand, as well as objects held by that hand, were used as targets to investigate the effects on size-constancy scaling of moving the hand to and fro along the line of sight for different distances in the dark. Results show that, when observers focus on a held object, the changes in size predicted by Emmert's law occur in response to both active and passive proprioceptive or haptic cues. The most intriguing result consisted of the finding that, when only the hand is the target, there appears to be a limit to the decrease in apparent hand size. It appears that the visual system 'refuses' to size-scale the hand below a limit it accepts as representative or acceptable of 'its' hand.

Adult↗
PubMed1999

The unseen color aftereffect of an unseen stimulus: insight from blindsight into mechanisms of color afterimages.

We show here that, in the absence of a direct geniculostriate input in human subjects, causing loss of sight in the visual half-field contralateral to the damage, the pupil responds selectively to chromatic modulation toward the long-wavelength (red) region of the spectrum locus even when the stimulus is isoluminant for both rods and cones and entirely restricted to the subjects' "blind" hemifields. We also show that other colors are less or wholly ineffective. Nevertheless, red afterimages, generated by chromatic modulation toward the green region of the spectrum locus, also cause constrictions of the pupil even when green stimuli are themselves completely ineffective in the blind hemifield. Moreover, human subjects with damage to or loss of V1 are typically completely unaware of the stimulus that generates the aftereffect or of the aftereffect itself, both of which can be seen clearly in normal vision. The results show that pupillary responses can reveal the processing of color afterimages in the absence of primary visual cortex and in the absence of acknowledged awareness. This phenomenon is therefore a striking example of "blindsight" and makes possible the formulation of a model that predicts well the observed properties of color afterimages.

Adult↗