Optical Illusions

We use a new objective measure of illusory contour strength, threshold reduction for aspect ratio discrimination, to examine the effect of dynamics and relative phase on the Kanizsa illusion. We found no dependence of illusory contour strength on the relative phase of flickering inducers (in phase, antiphase, or in quadrature phase) either for the standard Kanizsa square, or for modifications that facilitated or interfered with amodal completion. Comparison with a vernier acuity task indicates that the distance between the inducers, rather than the nature of the task, accounts for the insensitivity to relative phase.

This article analyzes the fundamental mechanism of vision from both neurobiological and philosophical perspectives. Rather than treating perception as a passive reflection of the world, it emphasizes that the eye encodes differences in brightness from the very beginning through ON and OFF receptive fields. As a result, vision operates as a dual prediction: of what becomes illuminated and of what becomes darkened. Only at later stages of neuronal integration are these contrasts combined into a coherent image, allowing perception to be understood as an act of reconstruction rather than passive registration. In philosophical terms, vision discloses a truth about reality: it does not appear as a direct image, but as a tension of differences, whose synthesis takes place within consciousness.

The place is Aliko Beach, Naxos Island, Greece. The time is 12:27 pm, August 2, 2020. The breeze of the Aegean Sea at the abandoned hotel on this low hill overlooking the sea allows my presence under the strong midday sun. I stand in the middle of a slightly discolored turquoise circle with a pointed arrow reading "point of view" (Fig. ). I adjust my body to the circle and my eyes follow the instructions on the floor. I'm staring at Beaching, as I would find out later. It depicts two colorful, supernaturally big birds. I wonder whether this is one of the many rare species residing in the fragile ecosystem of the area that was disturbed when this hotel was erected in the early 1970s. The bird feathers somehow resemble the local famous cedar forest. The pictorial scene is completed with a blue sky and a beach fusing the drawing with the reality. Of course, this is not my first encounter with WD's work. Yet, it is the first time that this encounter is directed. I look around and see more WD pieces and couldn't resist exploring the entire site. I start walking and remember the words of urban designer Gordon Cullen (1961, 118) on embodied perception: we apprehend space "through kinesthetic experience." Gorillas, sea dragons, elves, three-eyed giants, and all sorts of exotic animals and surreal creatures inhabit the abandoned hotel. But they don't just occupy they walls. WD's pieces interact with them: they extend them, offering (an illusion of) depth, openings and materiality, to name a

This research project was an unusual one. It did not involve primary data collection but , rather , was a systematic review of a large data base , the extraction of the general implications of that data , and their synthesis into an organizing taxonomy. This project was sponsored by the Engineering Psychology Programs of the Office of Naval Research with supplemental support from the Air Force Office of Scientific Research and AMD/RDO (USAF). I am especially grateful to the ONR 's Dr. Martin A. Tolcott , Director of Engineering Psychology, and Dr. John 3. O'Hare , scientific officer for the project , for their encouragement throughout the course of this project. -. Dr. O ~Hare I s contributions, in particular , were far greater than his administrative responsibility would indicate. His jud gment about matters of general organization and his detailed commentary on some of the chapters were especially appreciated. The latter part of the book was written while I was on sabbatical leave at the University of Hawaii. I am grateful to Dr. Robert Cole, Chairman of the Department of Psychology there, for making that visit possible. I also was pleased to have the sabbatical extended beyond a minimum duration by a James McKeen Cattell sabbatical supplement award. The continued courtesies of Dr. Robert L. Thorndike, secretary-treasurer of the fund , throughout the course of my sabbatical are gratefully acknowledged. Much of the typing of the manuscript has been carried out by Suzanne Gurney, to whom I hereby extend my thanks for her patience with the roughness of my rough drafts.

This study explored the ability of observers to recognize very sparsely sampled, stereoscopic, dotted surfaces. The observers' performance exceeded that of a simple surface-fitting algorithm that served as a first approximation model to the solution ofthe perceptual problem. We explored various attributes ofthe stimulus surfaces, but were unable to find any single attribute that could account for the measured performance. Therefore, we propose that the observers used several global surface attributes jointly to distinguish one form from another. Collectively, these attributes define what is meant by form in this study. We suggest that our results argue for a globally precedent, multidimensional model ofform reconstruction as opposedto a local-feature, unidimensional interpretation. How do observers reconstruct percepts from abstractions or caricatures that only sparsely sample a stimulus object? For many decades it has been quite clear that the human visual system has a powerful ability to fill in, close, and perceptually complete partial stimuli. Examples of completion phenomena are ubiquitous in geometric illusions, in the work of the Gestalt psychologists (as discussed, for example, in the work of and in many reports by contemporary perceptual researchers. Modern artists also take advantage of this ability to perceptually complete by suggesting complex images with simple abstractions of reality rather than by photographic reproduction of the full details of a scene. The ability to reconstruct images is so powerful that it is often difficult to convince an observer that an object that was perceived was not, in fact, present. In one wellknown example, a carefully designed demonstration is required to convince an observer that each retina possesses a 5 0-wide lacuna, Pursuing another proof of our reconstructive abilities, Townsend and Ashby (1982) showed that observers viewing stimuli that were close approxi-

It is well known that context influences our perception of visual motion direction. For example, spatial and temporal context manipulations can be used to induce two well-known motion illusions: direction repulsion and the direction after-effect (DAE). Both result in inaccurate perception of direction when a moving pattern is either superimposed on (direction repulsion), or presented following adaptation to (DAE), another pattern moving in a different direction. Remarkable similarities in tuning characteristics suggest that common processes underlie the two illusions. What is not clear, however, is whether the processes driving the two illusions are expressions of the same or different neural substrates. Here we report two experiments demonstrating that direction repulsion and the DAE are, in fact, expressions of different neural substrates. Our strategy was to use each of the illusions to create a distorted perceptual representation upon which the mechanisms generating the other il...

The Shroud of Turin image formation involves specific molecular transformations of cellulose through a threestep photochemical process: dehydration, oxidation, and conjugation 1,2. This document provides detailed analysis of the chemical mechanisms that convert colorless cellulose into the characteristic yellow-brown chromophores observed in the image areas 4,13, examining the molecular pathways, intermediate compounds, and final conjugated structures responsible for the visible coloration.

The perceived blur of drifting sinusoidal gratings was compared to that of static, blurred "square wave" gratings before and after adaptation to a missing fundamental (MF) pattern. The results indicate that the perceived blur of a drifting sine grating is inversely related to its drift speed. However, after adaptation to a MF pattern, this effect is reduced. The adaptation effect is most profound for low contrast gratings. The results provide tentative evidence for a non-linear stage in motion processing which serves to introduce higher frequencies into the neural image which are not present in the original signal.

The brain processes many aspects of the visual world separately and in parallel, yet we perceive a unified world populated by objects. In order to create such a "bound" percept, the visual system must construct object-centered representations out of separate features and then maintain the representations across changes in space and time. Here, we examine the role of features themselves in maintaining and disambiguating the representations of the objects to which they belong. In three experiments, we measure how the perceived motion of two objects traversing ambiguous trajectories is affected by the contrast between the features and surrounding fields, by the contrast between features, and by changes to orientation of texture within objects. We report that the maintenance and disambiguation of object representations depend on the contrast of the features relative to their surrounds and on the extent of feature differences between the two objects. These feature dependencies indicate that object representation relies on relative response to many stimulus dimensions.

REPT DOCUMENTA TION PAGE "READ INSTRUCTIONS P TA PELFORE COMPLETING FCRM I. REPORT NUMBER 12. GOVT ACCESSION NO. 3. RECIPIENT'S CATALOG NUMBER SAFOSR-TR" -03 -0 371 7? , 4, TITLE (and Subitle) S. TYPE OF REPORT a PERIOD COVERED * Velocity Discrimination in the Peripheral Research Progress and Visual Field Forecast Report 6. PERFORMING ORG. REPORT NUMBER S 7. AUTHOR(a) 8. CONTRACT OR GRANT NUMBER(a)

In this paper, I present NPI-Theory as a falsifiable hypothesis, rendering it as an objectively plausible view of the real world. The paper integrates scientific research and empirical fact, and provides the outline for an experiment to test the hypothesis as illusion susceptibility in developmental psychology.

The term colour constancy is not defined in the CIE International Lighting Vocabulary, and has been understood differently by different authors, some of whom hold that it should not be used at all. For this article I define colour constancy as the relative stability of the colour we perceive as belonging to an object under varying viewing conditions, including varying illumination. In this sense, colour constancy is the way in which we experience the ability of our visual system to arrive at a relatively consistent estimate of overall spectral reflectance under varying viewing conditions
Colour constancy is normally very high under varying intensities of the same illumination, and diminishes under illumination differing in perceived colour. However, even under quite strongly coloured illumination, the degree of colour constancy our visual system achieves can be remarkable compared to the variation in the stimulus available to it. Paradoxically, the automatic mental processing that enables colour constancy in our perception of most objects in the world can result in dramatic failures of colour constancy in our perception of areas of images, and it's precisely the high level of colour constancy we usually experience, especially under varying intensities of the same illumination, that leads us to think of object colours as fixed, intrinsic properties of objects, and so to find these failures of colour constancy in our perception of image areas so alarming.

Psychophysical studies of change blindness indicate that, at any instant, human observers are aware of detail in few parts of the visual field. Such results suggest, to some theorists, that human vision reconstructs only a few portions of the visual scene and that, to bridge the resulting representational gaps, it often lets physical objects serve as their own short-term memory. We propose that human vision reconstructs no portion of the visual scene, and that it never lets physical objects serve as their own short-term memory.

The ability of subjects to detect whether a structure-from-motion display depicts one or two rigid objects was examined in the presence or the absence of noise points. Each object was composed of a set of points chosen randomly within the volume of a sphere. The objects rotated rigidly about different axes passing through the center of the sphere. For displays without noise points, detection increased with larger angles between the rotation axes and with more points in each object. For displays in which noise points were present, detection was above chance but, in general, worse than that for displays without noise points. The implications of these results for image segmentation in complex motion patterns is discussed.

We describe two psychophysical experiments testing predictions of the square difference mechanism we have previously proposed for intensity-based stereo. Experiment 1 assesses the relative contributions of disparity and contrast to intensity-based stereo by measuring detection thresholds. The product of disparity and contrast at threshold is shown to be constant. In experiment 2, we measure quantitatively the global depth position perceived in stereograms of curved, smoothly shaded surfaces. The results show that disparity averaging over the surface involves a contrastdependent weighting function. The results from both experiments are consistent with predictions derived from the square difference mechanism. The relation of this mechanism to feature correspondence stereopsis and shape-from-shading is discussed and a general framework for assessing the modularity of stereopsis is presented.

The perceived position of a stationary Gaussian window of a Gabor target shifts in the direction of motion of the Gabor's carrier stimulus, implying the presence of interactions between the specialized visual areas that encode form, position, and motion. The purpose of this study was to examine the temporal and spatial properties of this illusory motion-induced position shift (MIPS). We measured the magnitude of the MIPS for a pair of horizontally separated (2 or 8 deg) truncated-Gabor stimuli (carrier = 1 or 4 cpd sinusoidal grating, Gaussian envelope SD = 18 arc min, 50% contrast) or a pair of Gaussian-windowed random-texture patterns that drifted vertically in opposite directions. The magnitude of the MIPS was measured for drift speeds up to 16 deg/s and for stimulus durations up to 453 ms. The temporal properties of the MIPS depended on the drift speed. At low velocities, the magnitude of the MIPS increased monotonically with the stimulus duration. At higher velocities, the magnitude of the MIPS increased with duration initially, then decreased between approximately 45 and 75 ms before rising to reach a steady-state value at longer durations. In general, the magnitude of the MIPS was larger when the truncated-Gabor or random-texture stimuli were more spatially separated, but was similar for the different types of carrier stimuli. Our results are consistent with a framework that suggests that perceived form is modulated dynamically during stimulus motion.

Previous studies indicated that less motion smear is perceived when a physically stationary target is presented during voluntary eye movements than when similar retinal-image motion occurs during steady fixation. In this study, we assessed whether the perception of motion smear is attenuated also during the involuntary vestibulo-ocular reflex (VOR). Normal observers matched the length of perceived smear in two experimental conditions that were designed to produce similar trajectories of retinal image motion. In the fixation condition, a small bright target was presented for a duration of 50-200 ms in rightward or leftward motion, while the observer remained stationary and maintained fixation. In the VOR condition, the target moved along with the observer, who underwent full-body rotation around a vertical axis in darkness. Horizontal eye movement recordings during VOR trials allowed us to calculate the velocity of retinal image motion on each VOR trial. The principal result was that the extent of perceived motion smear was significantly less during VOR than fixation trials, particularly for target durations of 100 ms or longer. These findings support the conclusion that extra-retinal signals during the involuntary VOR contribute to a reduction of perceived motion smear.

Wemeasured errors in estimating the absolute time to collision with a simulated approaching textured object. The texture elements were circular bright dots. When we matched the rate of angular expansion of the simulated object, the rate of expansion of the texture dots, and the rate of increase of dot separation, so as to accurately simulate an approaching object, errors were small underestimations that were independent of dot size (mean of 3.2%). When dot angular size was held constant during the simulated approach, errors were the same as when the simulation was accurate, provided that dot size was less than 2.2-4.4 min of arc. As dot size was progressively increased, errors changed to overestimations. For the largest dot size used (10.5 min of arc at time t =0), time to collision was overestimated by up to 21%. A sufficiently large overestimation would mean that measures taken to avoid collision would be too late. Wesuggest that the relevance to everyday life of data on the perception of motion in depth and self-motion collected using constant-sized dot displays might be questionable if dot size exceeds 2.2-4.4 min of arc. GENERAL METHOD (Hoyle, 1957; Lee 1976), where Tis the time to collision with the object and IIis the object's instantaneous angular subtense. A square array of bright circular dots was generated by a PC (Dell Dimension XPS, Pentium 100 MHz with 30 MB RAM) and displayed on a computer monitor running at 30 frames/sec with a resolution of 600 (horizontal) X 480 pixels. The display (Dell Ultrascan ISTE monitor) was viewed binocularly from 580 em, at which distance it subtended 2.7°X 2.1°. The luminance profile along any diameter of any given dot was a Gaussian wave form. The following three variables could be manipulated independently: the side length (11°) of the square array of dots, dot diameter (s), and dot separation (x). The total number of dots in the array depended on dot size, dot separation, and the mode of expansion, as is described below. For a rigid nonrotating object that is moving directly toward the eye at constant speed, it has been shown that

Wemeasured errors in estimating the absolute time to collision with a simulated approaching textured object. The texture elements were circular bright dots. When we matched the rate of angular expansion of the simulated object, the rate of expansion of the texture dots, and the rate of increase of dot separation, so as to accurately simulate an approaching object, errors were small underestimations that were independent of dot size (mean of 3.2%). When dot angular size was held constant during the simulated approach, errors were the same as when the simulation was accurate, provided that dot size was less than 2.2-4.4 min of arc. As dot size was progressively increased, errors changed to overestimations. For the largest dot size used (10.5 min of arc at time t =0), time to collision was overestimated by up to 21%. A sufficiently large overestimation would mean that measures taken to avoid collision would be too late. Wesuggest that the relevance to everyday life of data on the perception of motion in depth and self-motion collected using constant-sized dot displays might be questionable if dot size exceeds 2.2-4.4 min of arc. GENERAL METHOD (Hoyle, 1957; Lee 1976), where Tis the time to collision with the object and IIis the object's instantaneous angular subtense. A square array of bright circular dots was generated by a PC (Dell Dimension XPS, Pentium 100 MHz with 30 MB RAM) and displayed on a computer monitor running at 30 frames/sec with a resolution of 600 (horizontal) X 480 pixels. The display (Dell Ultrascan ISTE monitor) was viewed binocularly from 580 em, at which distance it subtended 2.7°X 2.1°. The luminance profile along any diameter of any given dot was a Gaussian wave form. The following three variables could be manipulated independently: the side length (11°) of the square array of dots, dot diameter (s), and dot separation (x). The total number of dots in the array depended on dot size, dot separation, and the mode of expansion, as is described below. For a rigid nonrotating object that is moving directly toward the eye at constant speed, it has been shown that

In this short essay, we introduce the difference between vision and perception. As a case example, we discuss some examples of perceptual deception concerning the alleged inscriptions and outlines of objects that some scholars perceive on one of the most debated low-contrast image: the body imprint on the Shroud of Turin.

Ambiguous figures attract observers because perception alternates between different interpretations while the sensory information stays unchanged. Understanding the underlying processes is difficult because the precise time instant of this endogenous reversal event needs to be known but is difficult to measure. Presenting ambiguous figures discontinuously and using stimulus onset as estimation of the reversal event increased temporal resolution and provided a series of well-confirmed EEG signatures. In the current EEG study we used this ‘onset paradigm’ for the first time with Boring's old/young woman stimulus. We found an early occipital event-related potential (ERP) correlate of reversals between the perception of the old woman and the perception of the young woman that fits well with previous ERP findings. This component was not followed by the often-reported occipito-parietal Reversal Negativity at 260 ms, but instead by an occipito-temporal N170, that is typically reported ...

The "Necker-Zeno model", a model for bistable perception inspired by the quantum Zeno effect, was previously used to relate three basic time scales of cognitive relevance to one another in a quantitative manner. In this paper, the model predictions are compared with experimental results obtained under discontinuous presentation of an ambiguous stimulus. In addition to earlier results for long inter-stimulus intervals, we show that the reversal dynamics according to the Necker-Zeno model is also in agreement with new results for short inter-stimulus intervals. Moreover, we refine the model in such a way that it accounts for the distribution of "dwell times" (inverse reversal rates). Finally, we indicate applications concerning the modification of cognitive time scales under conditions of psychopathological impairments and meditationinduced modes of awareness.

Two line gratings abutting each other with a phase shift of half a cycle elicit the perception of an illusory line running orthogonany between the two sets of grating lines. We found that rating strength increases with increasing number of lines, line length, and phase angle. In contrast, rating strength decreases with increasing spacing of lines, lateral misalignment, rotation of one grating relative to the other, and line width. There is a pronounced oblique effect at 45 deg when the orientation of the abutting gratings is changed from horizontal through diagonal to vertical. Findings are interpreted in terms of a neurophysiological model. We conclude that the end-stopped receptive fields activated by the grating lines are about 6 deg long and 2 deg wide. On the other hand, the "response fields" of the cells, integrating orthogonally across line ends, are assumed to be 5 deg long and less than 1 deg wide. The psyehophysical data compare favorably with available neurophysiological data in Area V2 of the macaque suggesting that the perception of illusory contours in human observers may be based on cortical cell properties similar to those found in the monkey.

How can our percept spontaneously change while the observed object stays unchanged? This happens with ambiguous figures, like the Necker cube. Explanations favor either bottom-up factors in early visual processing, or top-down factors near awareness. The EEG has a high temporal resolution, so event related potentials (ERPs) may help to throw light on these alternative explanations. However, the precise point in time of neural correlates of perceptual reversal is difficult to estimate. We developed a paradigm that overcomes this problem and found an early (120 ms) occipital ERP signal correlated with endogenous perceptual reversal. Parallels of ambiguous-figure-reversal to binocular-rivalry-reversals are explored.

Normally we experience the visual world as stable. Ambiguous figures provide a fascinating exception: On prolonged inspection, the ''Necker cube'' undergoes a sudden, unavoidable reversal of its perceived front-back orientation. What happens in the brain when spontaneously switching between these equally likely interpretations? Does neural processing differ between an endogenously perceived reversal of a physically unchanged ambiguous stimulus and an exogenously caused reversal of an unambiguous stimulus? A refined EEG paradigm to measure such endogenous events uncovered an early electrophysiological correlate of this spontaneous reversal, a negativity beginning at 160 ms. Comparing across nine electrode locations suggests that this component originates in early visual areas. An EEG component of similar shape and scalp distribution, but 50 ms earlier, was evoked by an external reversal of unambiguous figures. Perceptual disambiguation seems to be accomplished by the same structures that represent objects per se, and to occur early in the visual stream. This suggests that low-level mechanisms play a crucial role in resolving perceptual ambiguity.

Looking back over 15 years of demonstrating visual phenomena and optical illusions on the Internet, I will discuss two major topics. The first concerns the methodology used to present interactive visual experiments on the web, with respect to (a) wide accessibility, ie independent of browser and platform, (b) capable and elegant graphic user interface, (c) sufficient computational power, (d) ease of development and, finally, (e) future-proofing in an ever-changing online environment. The second major topic addresses some aspects of user behaviour, mainly temporal patterns (eg changes over weeks, years, long term), which reveal that there are more visitors during office hours.

Adapting motion was intermittent. The duty cycle of 33% remained constant across adaptation conditions while the number of onsets was varied. Onset rates of 1.4/s, 2.8/s, and 5.6/s were evaluated. Continuous motion and stationary adaptation served as controls.

During observation of an ambiguous Necker cube, our percept changes spontaneously although the external stimulus does not. An EEG paradigm allowing time-resolved EEG measurement during endogenous perceptual reversals recently revealed a chain of ERP correlates beginning with an early occipital positivity at around 130 ms (Reversal Positivity, "RP"). In order to better understand the functional role of this RP, we investigated its relation to the P100, which is spatiotemporally close, typically occurring 100 ms after onset of a visual stimulus at occipital electrodes. We compared the relation of the ERP amplitudes to varying sizes of ambiguous Necker cubes. The main results are: (1) The P100 amplitude increases monotonically with stimulus size but is independent of the participants' percept. (2) The RP, in contrast, is percept-related and largely unaffected by stimulus size. (3) A similar pattern to RP was found for reaction times: They depend on the percept but not on stimulus size. We speculate that the P100 reflects processing of elementary visual features, while the RP is related to a processing conflict during 3D interpretation that precedes a reversal. The present results indicate that low-level visual processing (related to stimulus size) and (relative) high-level processing (related to perceptual reversal) occur in close spatial and temporal vicinity.

https://issuu.com/sng.sk/docs/365_2_web

This essay explored the global phenomenon of Pop as an expanded cultural, artistic, and political condition rather than a narrowly defined Anglo-American movement. Drawing on recent international exhibitions (International Pop, The World Goes Pop*, Ludwig Goes Pop + The East Side Story), the text situates Pop within the turbulent geopolitics of the 1960s and early 1970s, tracing its reverberations across Western Europe, Latin America, Japan, and Central and Eastern Europe.

Framing Pop as the "birth of today," the essay reflects on its rebellious embrace of consumer imagery, popular culture, psychedelia, sexuality, science fiction, and spiritual hybridity. Special attention is paid to the Slovak and Czechoslovak neo-avant-garde, including artists such as Július Koller, Stano Filko, Jana Želibská, Peter Bartoš, and Alex Mlynárčik. These artists engaged with Pop’s visual strategies to express both personal mythologies and socio-political critique within socialist conditions.

The text highlights how feminist, conceptual, and anti-establishment currents intersected with Pop aesthetics, particularly through Želibská’s gender-conscious environments and Koller's “sci-fi” material realism. Drawing connections to surrealism, Nouveau Réalisme, capitalist realism, and Fluxus, the essay proposes a more layered, transnational, and politically nuanced understanding of Pop—one that includes its global counter-histories, critical reappropriations, and local utopias. It argues for Pop not just as an art movement, but as a mode of seeing, archiving, and performing contemporary life.

Conventional approaches to color assume its origin in external electromagnetic spectra. However, these models inadequately describe phenomena such as subjective color perception, color memory, and synesthetic resonance. This paper introduces a phase-density framework for color based on the admission function φₑ(x, t, λ̂), integrating spectral entry, neural permission thresholds, and temporal modulation.


Using the Color Tuning Fork Integral (I_res) and the perceptual density formula P_color = I_res / ε_{color}, we demonstrate that color is neither fixed nor purely spectral — but a structural response to admissibility within brain-bound phase conditions. This model opens pathways for instrumentation, perceptual diagnostics, and a neuro-symbolic definition of "color."

This philosophical and metaphysical essay explores the spiritual degradation of the human soul in the age of kleptocracy — a system where the sacred is inverted and replaced by material obsession. Through symbolic imagery — such as Living Water, gold as a dissolving alchemical fluid, and alcohol as counterfeit grace — the author reveals how the soul, once attuned to higher meaning, becomes diluted by false substitutes. The “wet soul” emerges as a metaphor for the loss of vertical spiritual orientation, while the “dry soul” symbolizes inner integrity, capable of burning with the fire of truth. The essay ends with a call to spiritual reawakening: as long as one soul remains dry, the fire of a new world may still be kindled.

У цьому філософсько-метафізичному есе автор досліджує природу сучасної душевної деградації у світі, де панує клептократія — духовно збочена форма влади, в якій сакральне підмінено матеріальним. Через символічні образи — Живої Води, золота як рідини, алкоголю як псевдоблагодаті — простежується втрата людством Внутрішнього Джерела, здатного насичувати істинним сенсом. Мокра душа постає як метафора втрати вертикалі Духу. У противагу їй — образ "сухої душі", здатної горіти і нести світло. У фіналі звучить заклик до духовного пробудження — бо навіть одна душа, що не розмокла, може стати вогнищем нового світу.

A flickering light can be seen during a saccadic eye movement as a pattern of contours known as a phantom array. On repeated pairs of trials, observers made saccades across a narrow (1 arc minutes), bright (10−4 cd/m2) source of flickering light and were required to detect the phantom array. On one of each pair of trials, chosen at random, the light flickered at 60 kHz and on the other at a frequency chosen in the range 1–11 kHz. In two such studies, a few observers were reliably able to discriminate 11 kHz from 60 kHz on the basis of the visibility of the phantom array. The average threshold at which the array was visible was about 6 kHz and therefore double that previously obtained with larger targets. Those observers who were able to see the phantom array tended reliably to report more symptoms of visual discomfort in everyday life.

Square-wave gratings with particular spatial characteristics in visual illusions. Patients with migraine are particularly susceptible to these illusions and report disc. it. Their discomfort tends to be greater when the gratings are illuminated by red light, a tendency 1 known by controls. Gratings that induce illusions have been found to impair the recognition of opt superimposed targets in headache-free control subjects. We measured the impairment of target detection under illuminants of various chromaticities in migraineurs with and without aura and in mat controls. Migraineurs with aura had significantly higher thresholds for target detection than either migraineurs without aura or controls; in addition, the effect of chromaticity was slightly more pronounced in both migraine groups than in the control group. These findings are consistent with a recent suggestion that migraine with aura might give rise to subclinical damage to the primary visual cortex

The visibility of stationary phantoms was measured by human observers in two experiments. The phantom visibility declined with the increase of the mean luminance of black[white inducing gratings, falling near to zero at a mean luminance high above 80 ed/m 2. The phantoms also disappeared when the red/green inducing gratings were subjectively equiluminant. The implications of these results are discussed in relation to the grating induction effect and to the functional correlations with the magnoceHular system's activity.

To determine whether the optical distortion produced by wearing a facemask under water causes a loss of visual position constancy, that is, whether it causes stationary objects to appear to move when the head is moved. FINDINGS Twice as much apparent object movement occurred under water than in air. Specific underwater adaptation procedures pro-duced a small reduction of object movement. APPLICATION The results indicate that the constancy of visual position is not maintained under water. Therefore, apparent movement of stationary objects should be added to the list of visual problems which confront Navy divers.

The perception of certain figures with illusory contours entails a reversal of figure and ground. It is hypothesized that this process occurs in two stages. First, some factor must suggest or cue the reversal. Experiments are described that isolate three such factors, namely, alignment of physically present contours, recognized incompletion of parts of the stimulus array, and set. Once cued, however, other experiments indicate that in a further stage of processing the solution is examined with respect to its compatibility with the stimulus display or with other perceptual properties to which the display gives rise. Only if such compatibility is present will the perception of a figure with illusory contours be maintained.

A decade ago, S. Aglioti, J. F. X. DeSouza, and M. A. published an experiment that has had a big influence on the way that visual information is thought to control human behavior. Their findings have often been simplified as suggesting that action is immune to perceptual illusions. The current authors critically analyze the 4 steps involved in this simplification and argue that research during the last 10 years has shown that the validity of 3 of the 4 steps is doubtful. They conclude that this experiment cannot be regarded as firm support for the 2-visual-systems hypothesis (i.e., that the ventral stream is for perception and the dorsal stream is for visually guided actions).

"Like an actor it masquerades in disguise. In the domain of religion it appears in the form of blind faith and wants to deceive us in the name of orthodoxy. In politics it wants to overpower us in the guise of nationalism. In learning and culture it makes an appeal to us in the name of our nation and country. It behoves us not to be taken in by these fictitious names. We must remember that the root cause of all this is nothing but narrow-mindedness."
- SPEECHES OF MAULANA AZAD
1947—1955
Publications Division
Ministry of Information & Broadcasting
Government of India
January 1956

Stroboscopic illumination of a rapidly rotating disk with radial spokes leads to a range of different stationary and moving images as the angular rotation frequency of the disk and the strobe frequency are varied. We compare predictions from the standard correlation model of motion perception with a model based on phase locking observed during periodic stimulation of an integrate-and-fire nonlinear oscillator. The close agreement between theoretical predictions and experimental observations suggests the possibility that periodic forcing of nonlinear neural oscillations may play a role in motion perception.

In this paper I examine the conceptions of enargeia purported by Epicurus and Philodemus of Gadara. For Epicurus, enargeia is an indispensable epistemological criterion which enables to separate truth from falsehood in both the realm of perception and the realm of opinion and thought. Philodemus of Gadara distances himself from this view: in Περὶ ποιημάτων he criticizes enargeia for its manipulative features, which
compromise clarity and appropriateness, namely the qualities of any poetic or prose composition.

A well-known perceptual illusion is the appearance of illusory bands of brightness just to either side of a luminance edge. A narrow band of increased brightness is seen just to the higher-luminance side of an edge and a narrow band of decreased brightness is seen just to the lower-luminance side of an edge (figure ). Known as Mach bands (eg Ratliff 1965), these illusory bands have often been ascribed to the perceptual consequences of lateral inhibition (illustrated in figure ), although other accounts of the illusion have been proposed . Here, we consider the dimensions of cortical coding of spatial attributes öorientation and spatial frequencyörather than the coding of edges in the spatial domain (luminance transitions across distance). Cortical suppression between neurons tuned to similar orientations or spatial frequencies (ie `neighboring' neurons along these dimensions) is well documented (see section 4). We suggest that this should cause perceptual enhancement at transitions (`edges') in orientation and spatial frequency when viewing many natural (broadband) scenes. That is, a transition from strong to weak content in the frequency domain (an `edge' or `step' in amplitude in the Fourier plane) should result in increased perceptual prominence of orientations (or spatial frequencies) near the transition at neighboring orientations (or spatial frequencies). To evaluate this conjecture, we first constructed the stimulus shown in figure . This pattern consists of a 458 range of orientations, all of the same physical contrast, with content at all other orientations at 0% contrast (ie not present). Thus, transitions from low-contrast to high-contrast content along the orientation dimension exist at AE228 from vertical. Indeed, viewing figure shows a striking illusion in which certain orientations are much more apparent than the others even though all orientations present are of identical physical contrast. This report quantifies the magnitude of the illusion and documents the wide generality of the illusion across a variety of stimulus conditions. In short, we show the existence of highly robust illusory bands within the Fourier plane (the spatial-frequency and orientation dimensions) at amplitude transitions along either of those dimensions.

Westheimer, Gerald and Eric J. Ley. Spatial and temporal integration of signals in foveal line orientation. J. Neurophysiol. 77: 2677–2684, 1997. The discrimination of the orientation of a line improves with line length, reaching an optimum when a foveal line is ∼0.5° long. We studied the effect of eliminating sections of the line, of displacing them out of alignment, and of delaying them. Orientation discrimination thresholds are only a little elevated when a 25-arcmin line is replaced by three equally spaced collinear 5-arcmin segments. Two collinear 5-arcmin segments show better thresholds than a single one when they are separated by as much as 20 arcmin. But thresholds are impaired by bringing line segments out of collinearity by as little as 1 arcmin. Asynchrony of up to 50 ms can be tolerated, but when the middle segment of a three-line pattern is delayed by ∼100 ms there is active inhibition, thresholds being now higher than when the middle segment is absent. It is concluded ...