Using afterimages for orientation and color to explore mechanisms of visual filling-in

Simulations of Grossberg's FACADE model of visual perception have previously been used to explain afterimage percepts produced by viewing a sequence of orthogonally oriented gratings. Additional simulations of the model are now used to predict new afterimage percepts. One simulation emphasizes that the afterimage percepts are the result of orientation afterresponses and color afterresponses that interact at a filling-in stage. We report experimental data that agree with FACADE's prediction. A second simulation emphasizes the properties of the model's filling-in stage and predicts a situation where the afterimage percept should not appear. We report experimental data indicating that this model prediction is incorrect. We argue that the model is unable to account for this result unless the filling-in stage mechanisms are different from a diffusive-type process. We propose an alternative mechanism, and simulations demonstrate the system's ability to account for the afterimage data.     

Cortical shape adaptation transforms a circle into a hexagon: a novel afterimage illusion

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.     

视觉负后像对视觉搜索效率的干扰效应

为了探究视觉负后像对视觉搜索效率是否会通过颜色这一特征产生干扰,结合Van Lier后像和视觉搜索范式,通过两个实验考察了负后像对视觉搜索效率的干扰效应,并对负后像填充区域和原始发生区域进行了对比。实验结果表明,在有负后像的情况下,视觉搜索效率明显降低,但是不同颜色之间的差异并不显著;而负后像填充区域的干扰效应要弱于原始发生区域。研究结论对于进一步提高视觉搜索效率的颜色设计以及视觉负后像的新研究方法具有重要的参考意义。     

Monocular and dichoptic interaction between afterimages

Two experiments were conducted in which an afterimage of a foveal grating in the right eye was observed either on its own or surrounded by a second afterimage. The separation and orientation of the lines comprising the surrounding afterimage, and the eye to which it was presented, were varied. The total duration of visibility of the central afterimage was reduced significantly when the dichoptic surround was separated from it by less than 5 deg. This interocular suppression was independent of the orientation of the lines in the surround afterimage. Presentation of a monocular surround increased the duration of visibility of the central afterimage only when the orientations of the lines in the center and surround were the same. Thus, two processes were operating to produce this pattern of results: interocular suppression and intraocular contour facilitation that occurs for lines in the same orientation.     

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.     

Modeling filling-in of afterimages

Van Lier, Vergeer, and Anstis (2009) reported that color information in a visual afterimage could spread across regions that were not colored in the inducing stimulus. The perceived color and shape of the afterimage could be manipulated by drawn contours that apparently trap the spread of afterimage color signals. They further hypothesized that the observed effects indicated a common mechanism for afterimage color filling-in and real-color filling-in phenomena. New simulations of the existing boundary contour system/feature contour system model of visual perception (Grossberg & Mingolla, 1985a, 1985b) demonstrate the connection between these phenomena.     

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.     

The equivalent background of bleaching

Stiles and Crawford proposed that a retinal region bleached by preexposure to intense light behaves as if it were illuminated by some steady veiling or background luminance. We test this notion by comparing the afterimage of a bleaching light with a steady (and retinally stabilized) light of adjustable intensity, in the manner of Barlow and Sparrock. With their matching procedure, and also with a new procedure, we find as they did that during the rod phase of recovery the afterimage does look like a stabilized field of an intensity which, presented as a background, brings visual sensitivity to the same level. It is as if the two conditions produce equal signals at some stage of the visual pathway. Liked Barlow and Sparrock we observe a rod-cone break in the afterimage matches. However, we argue that the appearance of the rod-cone break presents a paradox and we show a way to resolve it.     

Types of attention matter for awareness: A study with color afterimages

It has been argued that attention and awareness might oppose each other given that attending to an adapting stimulus weakens its afterimage. We argue instead that the type of attention guided by spatial extent and perceptual levels is critical and might result in differences in awareness using afterimages. Participants performed a central task with small, large, local, or global letters and a blue square as an adapting stimulus in three experiments and indicated the onset and offset of the afterimage. We found that increases in the spatial spread of attention resulted in the decrease of afterimage duration. In terms of levels of processing, global processing produced larger afterimage durations with stimuli controlled for spatial extent. The results suggest that focused or distributed attention produce different effects on awareness, possibly through their differential interactions with polarity dependent and independent processes involved in the formation of color afterimages.     

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.     

The time course of visual afterimages: data and theory

Sequential viewing of two orthogonally related patterns produces an afterimage of the first pattern (Vidyasagar et al, 1999 Nature 399 422-423; Francis and Rothmayer, 2003 Perception and Psychophysics 65 508-522). We investigated how the timing between the first stimulus (a vertical bar grating) and the second stimulus (a horizontal bar grating) affected the visibility of the afterimage (a perceived vertical grating). As the duration from offset of the first stimulus increased, reports of afterimages decreased. Holding fixed the total time from offset of the first stimulus and increasing the duration from offset of the second stimulus while decreasing the time between the first and second stimuli, caused a decrease in afterimage reports. We interpret this finding in terms of Grossberg's BCS - FCS (boundary contour system--feature contour system) theory. In this theory, the afterimage percept is the result of color complement after-responses in the FCS system interacting with orientation after-responses in the BCS system. The two types of after-responses interact at a stage of neural filling-in to produce the afterimage percept. As the duration between the stimuli increases, the color after-responses weaken so that visible filling-in is less likely to occur. A similar effect occurs for the orientation after-responses but at a faster time scale. Simulations of the model match the experimental data.     

The Beholder's Eye: Vision and Perception in Afterimage Studies of Attitude Change

Prominent studies using the afterimage in attitude change were reviewed and critiqued using a closer understanding of the physiology of the eye. Given the way that the eye creates afterimages, it is suggested that Moscovici and Personaz' (1980) original findings could be re-interpreted. Using evidence from subsequent work on the afterimage effect, the author suggests a re-interpretation using Nemeth's (1986 ) divergent thinking hypothesis. Possible explanations of blue-green afterimage experiments and opportunities for future research are explored.     

The role of iris pigmentation in the perception of an afterimage

Duration, direction-change frequency, and color-change frequency of an induced afterimage were investigated as a function of iris pigmentation (blue or brown) and the wavelength of a light pulse used to bleach retinal photoreceptors. For blue-irised subjects, a yellow (Wratten 9) pulse produced the longest enduring afterimage while a blue-green (Wratten 44A) pulse produced the shortest enduring afterimage. The reverse was true for brown-irised subjects. Neither of the other dependent measures was affected by iris pigmentation or by pulse color. The afterimage duration results were explained in terms of the possible role of the iris in selectively and differentially filtering various wavelengths of light as a function of its pigmentation.     

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.     

Apparent afterimage size, Emmert's law, and oculomotor adjustment

The apparent size of an afterimage viewed from distances between 5 cm and 580 cm was matched to that of a size-adjustable stimulus at a fixed distance (20, 30, 90, and 200 cm). The experiment was conducted under normal indoor illumination with a procedure that facilitated matching for angular size. The matched size was found to increase with focal distance within 1 m and very little beyond 1 m. Similar results were obtained with an equivalent series of real stimuli subtending a constant visual angle. These findings suggest a scaling in perceived angular size in proportion to the oculomotor adjustments for accommodation and convergence. The observations of perceived angular size of the afterimage complement what Emmert's law is meant to describe (perceived object size of the afterimage), even though as the focal distance decreases it may be increasingly difficult to tease out perceived object size and perceived angular size with the matching procedure.     

Effects of voluntary attention on structured afterimages

The effect of voluntary attention on afterimage fragmentation was explored in two experiments. The afterimage, in the form of a 30 degrees-tilted star of David, was generated after prolonged steady fixation in the first experiment, and with a brief and intense flash in the second experiment. Subjects were instructed to select various target shapes in the afterimage for attention and, at the same time, observe what was visible or invisible. Verbal reports and manual responses to afterimage changes were analyzed. Attended shapes were found to disappear from awareness Faster than unattended ones (experiment 1), and complementary shapes were found to predominate visual awareness when one of the pair was selected for attention (experiment 2). Voluntary attention was also found to affect closure (filling-in of enclosed regions) and smoothing of line figures in afterimages.     

Afterimage oscillation after a brief light flash

Abstract: To investigate whether oscillation might appear not only in brightness but also in color dimension, we performed the following two experiments. In Experiment 1 subjects were asked to observe a moving dim light slit in the darkness with their right eye focused on a fixation point, which resulted in an afterimage appearing like a comet’s trail after the slit. The trail oscillated rapidly in brightness (four/five times), and soon disappeared. In Experiment 2, an afterimage generated by an intense color disc (S1) was projected onto a dim white disc (S2) after a controlled period of interstimulus interval. The white disc appeared oscillating slowly between the similar color and the complementary color, at least twice in approximately 40 s. The results of these experiments led us to infer that afterimage oscillations occur in both brightness and in color dimension. These oscillations are closely correlated with those caused by two physiological mechanisms: the magnosystem generating the brightness oscillation, and the opponent‐color site of the parvosystem generating the color oscillation.     

Imagery vividness, hypnotic susceptibility, and the perception of fragmented stimuli

Two experiments were conducted to determine the role of hypnotic susceptibility level (high or low) and imaging ability (vivid or poor) in the performance of gestalt closure tasks. In Experiment 1, subjects were required to identify fragmented stimuli in the Closure Speed Test and in the Street Test. In Experiment 2, subjects reported on fragmented stimuli that were projected to the right eye and subsequently produced an afterimage. Individuals were asked to identify the composite if possible and to report on the duration of the afterimage. In both experiments, hypnotic susceptibility level and imaging ability affected reports of gestalt closure. The greatest number of correct closures was reported by those who were both high in hypnotic susceptibility and vivid in imaging ability. In addition, in the second experiment, this group also reported the longest enduring afterimage. These results are discussed in terms of the processes required to perform in a gestalt closure task.     

A study of afterimages generated by monocular and dichoptic viewing

Fragmentation of a prolonged afterimage of a vertical bar viewed monocularly against a background of either horizontal or vertical stripes was investigated. The background of vertical stripes produced greater partial fragmentation of the bar than did the horizontal background. This effect was not found for binocular viewing, in which the afterimage was viewed against a background seen by the other eye. Implications for present theories of fragmentation are discussed.     

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.