Formation Of Afterimages Research Articles

After-image formation by adaptation to dynamic color gradients

The eye’s retinotopic exposure to an adapter typically produces an after-image. For example, an observer who fixates a red adapter on a gray background will see an illusory cyan after-image after removing the adapter. The after-image’s content, like its color or intensity, gives insight into mechanisms responsible for adaptation and processing of a specific feature. To facilitate adaptation, vision scientists traditionally present stable, unchanging adapters for prolonged durations. How adaptation affects perception when features (e.g., color) dynamically change over time is not understood. To investigate adaptation to a dynamically changing feature, participants viewed a colored patch that changed from a color to gray, following either a direct or curved path through the (roughly) equiluminant color plane of CIE LAB space. We varied the speed and curvature of color changes across trials and experiments. Results showed that dynamic adapters produce after-images, vivid enough to be reported by the majority of participants. An after-image consisted of a color complementary to the average of the adapter’s colors with a small bias towards more recent rather than initial adapter colors. The modelling of the reported after-image colors further confirmed that adaptation rapidly instigates and gradually dissipates. A second experiment replicated these results and further showed that the probability of observing an after-image diminishes only slightly when the adapter displays transient (stepwise, abrupt) color transitions. We conclude from the results that the visual system can adapt to dynamic colors, to a degree that is robust to the potential interference of transient changes in adapter content.

Cortical mechanisms for afterimage formation: evidence from interocular grouping

Whether the retinal process alone or retinal and cortical processes jointly determine afterimage (AI) formation has long been debated. Based on the retinal rebound responses, recent work proposes that afterimage signals are exclusively generated in the retina, although later modified by cortical mechanisms. We tested this notion with the method of “indirect proof”. Each eye was presented with a 2-by-2 checkerboard of horizontal and vertical grating patches. Each corresponding patch of the two checkerboards was perpendicular to each other, which produces binocular rivalry, and can generate percepts ranging from complete interocular grouping to either monocular pattern. The monocular percepts became more frequent with higher contrast. Due to adaptation, the visual system is less sensitive during the AIs than during the inductions with AI-similar contrast. If the retina is the only origin of AIs, comparable contrast appearance would require stronger retinal signals in the AIs than in the inductions, thus leading to more frequent monocular percepts in the AIs than in the inductions. Surprisingly, subjects saw the fully coherent stripes significantly more often in AIs. Our results thus contradict the retinal generation notion, and suggest that in addition to the retina, cortex is directly involved in the generation of AI signals.

Valoración de la formación de postimágenes mediante una nueva aplicación informática en pacientes con neuropatías ópticas desmielinizantes

The perception of colour is one of the visual functions affected by optic neuritis. Most of the tests currently available for evaluating dichromatism are based on assessing the hue, but no clinical studies have been conducted to investigate the formation of afterimages on the retina of these patients. To evaluate the dichromatism acquired in demyelinating optic neuritis by means of the formation of afterimages on the retina. This is an observation-based, cross-sectional, case-control study. The cases are patients with at least one bout of optic neuritis and confirmed multiple sclerosis. A healthy age- and sex-paired control was selected for each case. The main variable is the capacity to see afterimages after saturation of the retinal photoreceptor cells. A specific computer application was developed to evaluate this phenomenon. The sample consisted of 30 cases and 30 controls (63% females; mean age: 33 years; range: 18-48 years). The cases showed less probability of seeing the afterimage (36.6% of the cases, while none of the controls failed to see an afterimage) and, if it was seen, it remained for less time. The ROC curve shows a sensitivity of 86.3% and a specificity of 83.3%. The odds ratio was 5 (95% confidence interval: 2.21-11.3) for the probability of seeing the afterimage in controls versus cases. Patients with at least one episode of optic neuritis presented a lower capacity to observe afterimages. The test is therefore useful in the assessment and follow-up of functional damage in demyelinating optic neuropathies.

Interocular grouping of negative afterimages after binocular rivalry

Afterimage (AI) formation is based on both retinal mechanisms and perception (Gilroy & Blake, 2005; Shimojo et al., 2001). Here we propose an amended view that AI can be formed independent of perception. Stimuli in each eye were a centrally presented 2 by 2 array of grating squares (1 cycle/deg). Each element subtended 3°. In one eye, gratings in two diagonal quadrants were vertical, while those in the other quadrants were horizontal. The orientations of the corresponding elements in the other eye were orthogonal. Complete interocular grouping might produce coherent percepts of single large vertical or horizontal gratings. While for incomplete grouping, one could perceive two types of partially integrated patterns. Otherwise, the monocular stimuli were perceived. Both during and after each induction period (55s), 10 subjects reported their percepts according to the 4 types. Surprisingly, although all types were perceived with close probability during induction (22.5% ~ 27.3%), subjects reported seeing the AIs of coherent patterns much more frequently (57.3%). Alternating presentation of the two inducers binocularly failed to reproduce this effect (N = 9). To ensure the observed effect was specific to AIs, we measured it with varied inducing contrasts [.04 .08 .16 .35 1]. For all the contrast conditions, the predominance for the coherent percepts was significantly higher (N = 20, p < .01) during the AI period (70.6%) than during the induction (< 38.6%). Because of micro eyemovements, AIs might be rendered blurry like low-pass filtered stimuli. So we filtered the inducers with a low-pass filter (< 0.5 cpd retained), but still observed similar effects (N = 16, coherent percepts: 74.5% (AIs) vs. < 41.9% (inducers)). These findings suggest that AI formation after binocular rivalry adaptation is strongly dominated by the mechanisms that favor coherent percepts, while during induction such effects could be largely corrected by monocular feed-forward signals. Meeting abstract presented at VSS 2015

Cortical Shape Adaptation Transforms a Circle Into a Hexagon

After viewing a colored figure on a uniform gray background, an observer will see a negative afterimage after the colored figure disappears. This study shows that the shapes of afterimages vary systematically according to the shape of the adaptation stimuli, a phenomenon that could be caused only by cortical shape adaptation. In the experiments reported here, participants typically saw a hexagonal afterimage after viewing a circle and sometimes saw a circular afterimage after viewing a hexagon. When observers were adapted to rotating circles or hexagons, which produced the same circular retinal painting, they reliably reported that afterimages of circles appeared as hexagons, and vice versa. Furthermore, the fact that this effect also arose through interocular transfer confirms that a cortical process with binocular inputs must have contributed to it. This novel finding reveals that afterimage formation is determined mainly by a cortical process, not by retinal bleaching, and that rival mechanisms detect corners and curves of shapes in cortical processing.

Correlated effects of attention and awareness on contrast threshold elevation but not on afterimage formation

Correlated effects of attention and awareness on contrast threshold elevation but not on afterimage formation

Palinopsia

Background Palinopsia is a visual phenomenon that has been associated with brain neoplasia, epilepsy, trauma, systemic disease, psychiatric illness, and illicit as well as prescribed drug use. Despite some resemblance to diplopia, polyopia, and physiologic afterimage formation, palinopsia is actually a distinct entity often suggestive of disease through its distinct signs and symptoms. Careful patient history, visual field testing, and neuroimaging are among the tools used to diagnose palinopsia. Case Reports Four case reports of patients with palinopsia are presented. With the first patient, the palinopsia was associated with extensive lysergic acid diethylamide (LSD) use. The second patient's palinopsia was determined to be secondary to head trauma from a motor vehicle accident. The third patient began to experience palinopsia after he had been prescribed trazodone for insomnia. The fourth patient was found to have multiple potential etiologies. These 4 unique patients highlight the causes and management of palinopsia. Conclusions Optometrists should be aware of the symptoms of palinopsia to enable them to recognize this phenomenon and minimize the chance of misdiagnosis. Learning the physiologic mechanisms behind this uncommon disorder can help the clinician correctly identify its cause. Although palinopsia itself is not a disease, it is indicative of a disease, and the symptoms of palinopsia may be a manifestation of a serious underlying systemic dysfunction that could warrant treatment. In addition, identifying the symptoms of palinopsia can put patients at ease with regard to the often disturbing visual symptoms.

Misbinding of color to form in afterimages

Under dichoptic viewing conditions, rivalrous gratings that differ in both color and form can give the percept of the color from one eye in part of the form in the other eye. This study examined the afterimage following such misbinding of color to form. The first experiment established that afterimages of the misbound percept were seen. Two possible mechanisms for the misbound afterimage are (1) persisting retinal representations that are rivalrous and subsequently resolved to give misbinding, as during rivalrous viewing, and (2) a persisting response from a central neural representation of the misbound percept with the form from one eye and color from the other eye. The results support afterimage formation from a central representation of the misbound percept, not from resolution of rivalrous monocular representations.

The Interaction between Binocular Rivalry and Negative Afterimages

Afterimage formation, historically attributed to retinal mechanisms, may also involve postretinal process. Consistent with this notion are results from experiments, reported here, investigating the interaction between binocular rivalry and negative afterimages (AIs). In Experiment 1, one eye was exposed to a grating never consciously experienced by the observer because this grating remained suppressed in rivalry throughout induction (the exclusively dominant stimulus was designed to preclude formation of an AI). As expected, the suppressed grating generated a vivid AI whose orientation could be accurately identified; not surprisingly, the strength of this AI varied with induction contrast. Experiment 2 revealed, however, that the strength of this AI produced during suppression was significantly weaker than the AI produced by that same stimulus when it was visible throughout the entire induction period, implying that some component of AI induction is susceptible to interocular suppression. In Experiment 3, AIs of dichoptic, orthogonally oriented gratings were induced in a way ensuring that one of the two gratings was exclusively dominant during the induction period. Dissimilar monocular AIs engaged in rivalry, as expected, but, surprisingly, the AI induced by the suppressed grating initially dominated. We offer two alternative accounts of this counterintuitive finding, both based on differential neural adaptation.

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.

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.

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.

A neural model of foveal light adaptation and afterimage formation.

Psychophysical research has documented the existence of three processes in light adaptation: a fast subtractive process, a divisive process that is fast at light onset and slower at light offset, and a very slow subtractive process (Hayhoe et al., 1987). In the neural model developed here, the fast subtractive process is identified with horizontal cell feedback onto cones and the divisive process with amacrine cell feedback onto bipolar cells. The very slow subtractive process is identified with the modulatory feedback circuit from amacrines via interplexiform cells to horizontal cells. A nonlinear dynamical model is developed incorporating these aspects of retinal circuitry along with both ON- and OFF-center M and P pathways. This model is shown to account for many aspects of foveal light adaptation, including negative afterimage formation, and to explain a number of the physiological differences between M and P ganglion cells, including their differing contrast-response functions.

Neuronal correlates of stimulus orientation and retinal motion, and their binocular interaction in the visual cortex of chronic cats: H. Noda, R. B. Freeman, Jr. and O. D. Creutzfeldt — Max Planck Institute of Psychiatry, Munich (W. Germany)

Afterimage formation, historically attributed to retinal mechanisms [1, 2, 3, 4], may also involve postretinal process [5, 6, 7]. Consistent with this notion are results from experiments, reported here, investigating the interaction between binocular rivalry and negative afterimages (AIs). In Experiment 1, one eye was exposed to a grating never consciously experienced by the observer because this grating remained suppressed in rivalry throughout induction (the exclusively dominant stimulus was designed to preclude formation of an AI). As expected, the suppressed grating generated a vivid AI whose orientation could be accurately identified; not surprisingly, the strength of this AI varied with induction contrast. Experiment 2 revealed, however, that the strength of this AI produced during suppression was significantly weaker than the AI produced by that same stimulus when it was visible throughout the entire induction period, implying that some component of AI induction is susceptible to interocular suppression. In Experiment 3, AIs of dichoptic, orthogonally oriented gratings were induced in a way ensuring that one of the two gratings was exclusively dominant during the induction period. Dissimilar monocular AIs engaged in rivalry, as expected, but, surprisingly, the AI induced by the suppressed grating initially dominated. We offer two alternative accounts of this counterintuitive finding, both based on differential neural adaptation.