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PubMed2006

Evaluation of cerebral dyschromatopsia using color afterimage.

Cerebral dyschromatopsia is traditionally evaluated by color discrimination tests such as the Farnsworth-Maunsell 100 Hue Test. These tests are also used to evaluate color-perception deficits caused by eye disease, and they do not tell us whether color perception is impaired in the eye or in the brain. Here, we used color afterimage to isolate color-perception deficits in the brain from those in the eyes, in a patient with cerebral dyschromatopsia. The results showed that the patient perceived color afterimage of yellow and blue with abnormal duration and chromaticity. On the other hand, the patient performed normally on the Farnsworth-Maunsell 100 Hue Test. We conclude that the color afterimage test would be useful to evaluate color perception in the brain.

Color Perception↗

PubMed1982

The delayed rod afterimage.

A flashed background, presented to a dark-adapted eye, can saturate the rod system, making an incremental test patch invisible. But as the afterimage decays, the test can be distinguished. Increment thresholds measured within the decaying afterimage exhibit Weber's law over a wide range. The Penn and Hagins model of rod kinetics correctly predicts Weber's law, but makes incorrect predictions of the latency for the detection to occur. A new model, involving two exponential decays, is able to accommodate the latency data, as well as Weber's law. The model also makes good predictions of the results when the stimulus duration is increased from 100 msec to 1 sec.

Afterimage↗

PubMed2005

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.

Adaptation, Ocular↗

PubMedDate not supplied

Using afterimages to test neural mechanisms for perceptual filling-in.

Many theories of visual perception propose that brightness information spreads from edges to define the perceived intensity of the interior of visual surfaces. Several theories of visual perception have hypothesized that this filling-in process is similar to a diffusion of information where the signals coding brightness spread to nearest neighbors. This paper shows that diffusive mechanisms fail to account for the characteristics of certain afterimage percepts that seem to be dependent on the filling-in process. A psychophysical experiment tests a key property of diffusion-based filling-in mechanisms and finds data that rejects this class of models. A non-diffusive based filling-in mechanism is proposed and is shown to act much like the diffusive based mechanism in many instances, but also produces afterimage percepts that match the experimental data.

Afterimage↗

PubMed2005

Surround-induced foveal afterimage pulsation: evidence for a long-range neural effect.

We demonstrate that an afterimage resulting from a strong foveal light flash can be made to pulsate by luminance modulation of a surrounding annulus as far as 8 deg away. Afterimage pulsation persists even if all artifacts due to pupil size, stray light and simultaneous contrast are ruled out. This suggests an origin by a long-range neural process acting from the remote surround. The effect is interpreted in terms of an adaptive gain control optimizing the responses of visual cells.

Adult↗

PubMed1981

Afterimage versus photographic ocular torsionometry.

Rotation of the eyeballs about the visual axis due to head tilt, counterocular torsion, can provide information relevant to the neuro-otologic status. Measurement of these reflexive movements, however, involves several difficulties. Two methods are examined: determinations by a behavioral afterimage technique are compared with those of a photographic method in the same subjects using a test-retest format. Results indicate that both procedures yield reliable measurements, and any differences tend to be inconsistent. Thus, the faster and less expensive afterimage technique appears suitable for many clinical purposes in assessing vestibulo-ocular function.

Adult↗

PubMed1977

Persistence of complementary afterimages as a function of adult age and exposure duration.

The persistence of complementary afterimages was studied in 36 young (X age 18.8 years) and old (X age 62.1 years) male and female subjects. Afterimage persistence was found to be a direct function of exposure duration and to be greater for the older subjects as compared with the younger ones. The interactions between age and duration and between presentation order and duration were also significant. The data extend support for the "stimulus persistence" model to age differences in retinal function.

Adolescent↗

PubMed1990

Stability of retinal correspondence during divergence: evaluation with afterimages and Haidinger brushes.

Retinal correspondence has been described as invariant during normal binocular vision. However, there is substantial evidence that casts doubt on this interpretation and implies that retinal correspondence varies under certain conditions. This article reports the results of two experiments that appraise the stability of correspondence during fusional vergence in persons with normal binocular vision. In the first experiment, afterimages stimulated vertically corresponding retinal meridians prior to divergence. Three of six subjects gave data that indicated a change in the afterimage alignment significantly different from chance. The second experiment determined corresponding retinal areas with Haidinger's brushes. When divergence was maximally maintained, all six subjects who could appreciate the low-contrast Haidinger's brushes on the randomdot background saw two brushes while stereopsis and fusion remained present. Increases in plus lens power increased estimated brush separation.

Afterimage↗

PubMed1976

Conditioning afterimages: a procedure minimizing the extinction effect of normal test trials.

Six subjects were trained on a conditioning schedule of ten trials a day for 25 days: a further 18 CS-US pairings were presented on 4 subsequent days. The tone employed as the CS was put on 30 sec before the presentation of a briefly illuminated visual target (the US) and maintained until terminated by the subject when his afterimages disappeared. This procedure allowed continuous monitoring of the evolution of the conditioned response (conditioned afterimages): directly for CRs with a latency of less than 30 sec which could occur on every training trial before the US was presented; indirectly from the changes in the duration of afterimagery following the presentation of the US. As every trial yielded some evidence about the evolution of the CR, unreinforced test trials were not necessary after every block of training trials so minimizing the extinction effect attributable to the presentation of an unreinforced CS. In the course of the experiment the mean duration of afterimagery increased almost fivefold with one subject showing a tenfold increase. Five of the subjects experienced visual images in response to the tone alone and were judged to be conditioned. The data are discussed in relation to the evolving levels of conditioning identified by Bzhalava (1958, 1965).

Acoustic Stimulation↗

PubMed1968

Is orientation-specific color adaptation in human vision due to edge detectors, afterimages, or "dipoles"?

After one looks alternately at red vertical and green horizontal stripes, vertical and horizontal white stripes appear greenish and pink, respectively. This color aftereffect might imply that contour-detecting cells participate in human vision, or might simply be due to afterimages. A procedure that precludes afterimages still yields aftereffects, but sensory units less complex than edge detectors could be responsible.

Afterimage↗

PubMed1992

Optical illusions in clinical dermatology: the Mach band phenomenon and afterimages.

A survey of dermatologists was conducted to determine whether the perceptions of afterimages and Mach bands impacted on clinical dermatology practice. 26.5% (13/49) of respondents indicated that they perceived one or both of these optical illusions. No false-positive potassium hydroxide interpretations of skin scrapings for hyphae were reported due to perceived afterimages, and no skin biopsies were reportedly performed as a result of Mach bands.

Adult↗

PubMed2002

Effects of negative afterimages in visual illusions.

We show that a broad class of visual illusions, including illusory motion, can be explained by the effects of negative afterimages. Two new illusions, illusory shading and illusory tilting, are devised on the basis of the proposed explanation. The general feature of these illusions is an alternation between a high-contrast (white or black) and a low-contrast (gray) local input signal, which can be caused either by eye motion over patterns of varied luminance or by a change in such patterns over time. A simple model of the local signal dynamics qualitatively reproduces the illusory effects by adding the negative afterimage to the original visual stimulus.

Afterimage↗

PubMed1974

Evidence of complementary afterimages in the pigeon.

Key pecking of pigeons was reinforced on a variable-interval schedule when ambient illumination came from a green light, but not when it came from a red, yellow, or white light. The different hues were randomly presented for periods of 30 sec each, with the restriction that white never followed red. After discriminative control was established, the pigeons were tested with the same procedure used during training, except that white sometimes followed red. Significantly more responses were made during white-following-red than during white following either green or yellow. These findings indicate that, in changing from red to white, complementary afterimages can be induced in pigeons for a brief period of time. By providing behavioral evidence for afterimages in the pigeon, this technique may be useful to research in comparative neurophysiology, animal discrimination learning, and theories of color vision.

Afterimage↗

PubMed1981

Eye-hand tracking using afterimages. Evidence that sense of effort is dependent on spatial constancy mechanisms.

Oculomotor tracking of one's unseen hand is greatly enhanced when a positive afterimage of the arm is projected onto its changing apparent position. The "afterimage arm" also influences the perception of real arm motion. The nature of this influence indicates that sense of effort or will derives from spatial computations potentially involving sensory and motor information about the ongoing orientation of the entire body.

Acoustic Stimulation↗

PubMed1979

Hypnotic susceptibility and the perception of afterimages and dot stimuli.

Three experiments were conducted to determine the relationship between hypnotic susceptibility level and the susceptibility to several perceptual phenomena. Experiment I required subjects to observe an induced afterimage in a light-proofed environment and to report the frequency of direction and color changes. In addition, subjects reported the persistence of the afterimage. Experiment II involved the observation of a black dot against a white background, with frequency of observed movement being the dependent measure. Experiment III was similar to the second experiment except that the stimulus was encompassed by a frame. In Experiments I and II, subjects judged high in hypnotic susceptibility reported perceiving the strongest effect. This phenomenon was virtually eliminated in the third experiment. These results were interpreted as supporting a process whereby subjects judged high in hypnotic susceptibility are better able to selectively attend to relevant cues in a stimulus array during conditions of perceptual impoverishment.

Attention↗

PubMed1993

Mathematical description and computer simulation of retinal cometlike afterimages: a modified neural equation with stability analysis.

A mathematical model for the spatiotemporal description of a well-known psychophysical phenomenon, the cometlike afterimage effect (CLAIE), is presented. The CLAIE occurs when a bright circular light spot moves slowly in the peripheral human retina. Under these conditions, the leading edge of the dot looks circular, but the trailing edge becomes elongated like a comet's tail whose length increases with speed and luminance, and the illusion is more prominent for photopic backgrounds. This cometlike motion smear is described on the basis of the temporal responsiveness and adaptation of rods. The model is an extension of an existing neural model of M. N. Oğuztöreli et al., with an additional term that allows prolonged saturation and long decay time following exposure to intense stimuli, and these effects are held responsible for the cometlike smear. The model predicts the response of photoreceptors through a nonlinear ordinary integrodifferential equation, which includes known biophysical terms for response dynamics, adaptation, saturation, and kinetics of intermediate components of the phototransduction process. The introduction of a saturation coefficient into the neural equation makes it possible to distinguish the different saturation thresholds of the rod-and-cone system. Numerical determination of the stationary solutions and complete linear stability analysis of the improved neural equation are given for a neuron of second order, and some computational results are presented for phase flows around different singular points in the phase field. A computer simulation based on the improved neural equation is presented for modeling the development and features of the CLAIE as a function of the speed and luminance of the stimulus and the background intensity. The computational results agree well with the psychophysical findings relating to the CLAIE.

Afterimage↗

PubMed1982

Assessment of retinal image displacement during head movement using an afterimage method.

An afterimage method has been used to measure retinal image displacement during binocular fixation with active head rotation about a vertical axis. The results confirm previously published reports that fixation accuracy in the horizontal direction deteriorates as a result of a head rotation. However, both retinal image displacements and fixation disparities were found to remain much smaller (by a factor of 3 and 8 respectively) than the values previously reported in the literature for similar head rotations (peak-to-peak amplitude: 20 degrees, frequency: 0.66 Hz). Moreover, our results show that fixation accuracy fell not only in the horizontal direction, but also in the vertical direction by about the same factor. It is concluded that eye-movement compensation of active head rotation may be much better than previously reported in the literature, and good enough to prevent deterioration of vision.

Afterimage↗

PubMed1984

Eye movements, afterimages and monocular rivalry.

The eye-movement/afterimage theory of "monocular rivalry" (MR) between gratings was tested and strongly supported. In three experiments perceptual dominance of vertical or horizontal components of the pattern and fluctuations in perceived contrast of a single grating were shown to depend on the nature of the preceding shift in fixation position in the manner predicted by the theory. In a fourth experiment the angular selectivity of these fluctuations was eliminated, as predicted, when appropriate eye movements were made. Fixation-contingent fluctuations became equally strong for 15 degrees and 90 degrees angles. Taken together with data on afterimages, the results appear to resolve most of the problems recently raised against the theory.

Afterimage↗