Plasmas: A New Class of Motion-Induced Brightness Illusion

Perception ◽  
1997 ◽  
Vol 26 (1_suppl) ◽  
pp. 16-16 ◽  
Author(s):  
P Tse

When a white figure is set in smooth continuous motion against a dark background, a ‘shadowy’ region forms around and behind it, somewhat similar to the wake that a boat leaves in water. Conversely, when a dark figure moves against a white background, this ‘wake’ appears lighter than the background. When several such figures move, these ‘wakes’ can link up in surprising ways. For example, if four white circles of radius r are positioned on a dark background at the vertices of an imaginary square whose width is, say, 4 r, and this imaginary square rotates about its centre, bands darker than the background form between the four circles, linking them through the centre. This ‘black cross’ is nonrigid, and is accompanied by dark ‘wakes’ on the outside of the circles. I call these illusory brightness regions ‘plasmas’. The relation of this effect to other motion-induced brightness illusions is considered. In particular, this effect has different properties than either induced gratings (McCourt, 1982 Vision Research22 119 – 134) or phantom gratings (Tynan and Sekuler, 1975 Science188 951 – 952). Plasmas are not due to retinal afterimages or persistence, since they form in regions never traversed by the moving figure. Nor are they an artifact of the computer screen, since the illusion occurs equally well in displays constructed from paper. Plasmas have the opposite phase relative to the inducing figure, disappear when a figure stops moving, are strongest at high background/inducer contrast, and are most visible when the luminance of the inducers is in the photopic range. Experiments measuring the strength of plasmas as a function of angular velocity and visual angle are described. A model is proposed according to which plasmas are due to a phase lag in luminance-edge induced lateral inhibition.

2019 ◽  
Vol 3 (1) ◽  
Author(s):  
Alexander Gyoshev ◽  

The study observes some of the most important details hidden in Kazimir Malevich’s abstract painting “Black Square on a White Background” (1915). Of central concern for the more adequate understanding of this intriguing piece of art is the tracking of its supposed relationship with the work of Alfons Alle – French writer known for his extravagant style and ideas. The differences between Alle’s painting entitled “Negroes Fighting in a Cellar at Night” and Malevich’s composition, both sharing similar themes, are analyzed in their specific historical and cultural context. Finally, there is a hypothesis about “Black Square on a White Background” as a work marked with a psychological projection that unfolds itself through the dark figure of the square, as an iconic image that still has an impact on the contemporary art and may serve as a key to some symbols of the present.


2020 ◽  
Author(s):  
Ian Christopher McManus ◽  
Paul Gesiak

The Dutch painter Piet Mondrian (1872-1944) is the archetypal modernist, with the paintings of his uncompromisingly austere mature period, comprised of a white background, black vertical and horizontal lines and occasional, areas of red, yellow or blue, being icons of modern design. His paintings also represent a rare opportunity to experiment on aesthetic composition, the paintings being simulated relatively easily on a computer screen, with participants manipulating them interactively.The founding father of experimental aesthetics, Gustav Theodor Fechner, described three research methods in his Vorschule der Aesthetik of 1876, the Method of Choice, the Method of Production and the Method of Use. Most empirical work has used the Method of Choice, whereby participants are shown two or more similar images and choose between them. Our first studies of Mondrian used the Method of Choice. A set of 25 original (‘O’) Mondrian paintings were synthesised on a screen, as also were two pseudo-Mondrians, (P1 and P2). The pseudo-Mondrians were created by randomly moving all of the horizontal and vertical lines in the painting by a small amount (for P1) or by a slightly larger amount (for P2). P1 and P2 therefore had the same broad structure as O, containing the same ‘words’ (components), using the same ‘deep structure’ or ‘syntax’, but with the composition varied only by altering the relative positioning of the lines (equivalent in linguistic terms to a different pattern of stress or emphasis – prosodics). For each of the 25 paintings we created O, P1 and P2, and participants compared O with P1, O with P2, and P1 with P2, making 75 paired comparison judgements overall.In five separate studies, totalling 277 participants, it was clear that original Mondrians could reliably be distinguished from pseudo-Mondrians, with some participants being more sensitive than others. Fechner’s Method of Production allows participants to manipulate the content of an aesthetic object, altering it until they feel that it is most satisfactory. We adapted this method so that participants were presented with a single Mondrian painting on a computer screen. By moving the computer mouse a vertical, a horizontal or both a vertical and a horizontal line in the Mondrian were moved up and down or sideways. The images were constrained so that the moving lines were yoked to other lines of the same directionality, so that several moved at the same time, and lines could never cross over each other (i.e. the syntax remained fixed, with only proportional arrangements being altered). The original Mondrian was always a possible outcome of moving the cursor.The Production studies manipulated 39 original Mondrian paintings, none of which were included in the set of 25 used in the Choice experiments. All of the 84 participants could therefore carry out both the Method of Choice and the Method of Production, the order of the two Methods being chosen at Random (and order having no effect upon the results).The most striking result was that although the 84 participants, as expected, had clear preferences in the Method of Choice for Mondrians over pseudo-Mondrians, using the Method of Production there was no evidence that participants produced images which showed any overall similarity to the original Mondrians.A detailed study of what participants were doing when they were using the Method of Production suggested that the complexity of the task, despite its relative simplicity, was too great for them. Despite only manipulating in a two-dimensional space (or sometimes a one-dimensional space), participants seemed to find the task difficult. The program always started with the cursor at one of the four corners indicating the maximum dynamic range of the cursor, and in many cases participants ended up either on one of the edges of the space or even in a corner. In most cases only a small proportion of the possible design space was sampled before a decision was made.Our paper will consider how people can and cannot make complex aesthetic choices across a range of possible stimuli. In particular we will suggest that much of the problem with the Method of Production is a problem of visual working memory, participants not being able to hold in their heads a range of previous images to compare with the current one which is shown on screen. The Method of Choice, in contrast, makes no demands at all upon visual working memory. Although computer design in principle allows an almost infinite space of possibilities to be explored, in practice the ability to do so usefully seems to be heavily constrained by the cognitive limits of human processing, meaning that design systems need careful ergonomic organisation to prevent such problems.


2010 ◽  
Vol 653 ◽  
pp. 463-487 ◽  
Author(s):  
A. R. SHENOY ◽  
C. KLEINSTREUER

The influence of aspect ratio (χ = diameter/thickness) on the vortex shedding behaviour of fixed, and freely moving, circular disk has been investigated numerically. The aspect ratio significantly changes the structure of the vortices shed from the disk, thus altering the fluid induced forces. Disks of χ = 2 and 4 were selected, and by choosing Re = 240 periodic behaviour was observed for both the ‘fixed’ and ‘freely’ moving disks. First, the vortex structures shed from a ‘fixed’ circular disk of χ = 2 and 4 were computed for Re = 240. This was followed by a computation of their trajectories falling ‘freely’ under the action of gravity at Re = 240. For the ‘fixed’ disk of χ = 2, periodic shedding of one-sided hairpin-shaped vortex loops was observed. The flow field had a spatial planar symmetry and the vortices were shed from the same location, resulting in an asymmetric lateral force on the disk. The Strouhal number (St), calculated using the fluctuation in the axial velocity in the far-wake, was 0.122. This vortex shedding behaviour is referred to as the ‘single-sided’ vortex shedding mode. For the ‘fixed’ disk of χ = 4, periodic shedding of hairpin-shaped vortex loops was observed from the diametrically opposite location of the disk. The flow field had a spatial planar symmetry, and also a spatio-temporal one, with respect to a plane orthogonal to the spatial symmetry plane. The shed vortices induced a symmetric lateral force on the disk with a zero mean. The computed Strouhal number, was equal 0.122, same as that for χ = 2. This vortex shedding behaviour is referred as the ‘double-sided’ vortex shedding mode. For the ‘freely falling’ disk of χ = 2, an oscillatory motion was observed in a plane with a 83° phase lag between the lateral and angular velocity. The Strouhal number (Stb), calculated using the oscillation frequency of the ‘freely’ falling disk was equal to 0.116, which is comparable to the St of the fixed disk. For a ‘freely falling’ disk of χ = 4, oscillatory motion was observed in a plane with a 21° phase lag between the lateral and angular velocity. The Strouhal number (Stb) was equal to 0.171, which differs from the St observed in the wake of the fixed disk.


2012 ◽  
Vol 512-515 ◽  
pp. 1784-1787
Author(s):  
Shan Yu Zhou ◽  
Long Quan Shao ◽  
Lin Lin Wang ◽  
Yuan Fu Yi ◽  
Bin Deng ◽  
...  

To evaluate the masking ability of IPS e.max all-ceramics system of HO series. IPS e.max Press HO ingots were fabricated into twenty cylindrical specimens (n=5) with the diameter of 13mm and four different thinknesses (0.4mm, 0.6mm, 0.8mm, 1.0mm). All specimens after veneered, gazed and cemented to metal substrate disks (thickness 3mm, diameter 13mm) were measured on both the white background and metal substrate disks background using a spectrophotometer and values of L, a and b were calculated to compare color differences among four groups. Meanwhile ΔE with the preselected required color (A2 color) were calculated. ΔE<1.5 was considered a clinically acceptable color match. In the 0.4mm thickness specimens group, the values of L, a and b significantly increased (-1.36±0.05, -0.15±0.06, -1.46±0.02, respectively) between the white background and abutment background. But there were no significant color differences in the other three groups (P<0.05). In the 0.6mm and 0.8mm thicknesses specimens groups, the color difference values (0.71±0.04, 1.14±0.06, respectively) with A2 color were less than the defined value. Thus the cylindrical specimens with the thickness of 0.6mm, 0.8mm and 1.0mm could mask the metal substrate disks background sufficiently and the thickness of 0.6mm and 0.8mm had an acceptable color match compared with the target color. IPS e.max all-ceramics system of HO series can produce clinically acceptable color match and have the capacity to mask a dark background such as a dark tooth or core buildup material.


1994 ◽  
Vol 47 (4) ◽  
pp. 865-893 ◽  
Author(s):  
Yehoshua Tsal ◽  
Lilach Shalev ◽  
Dan Zakay ◽  
R.E. Lubow

The effects of attention on brightness perception was investigated in four experiments. In the first three, subjects estimated the brightness of a briefly presented small grey square by selecting a number that corresponded to one of four possible squares varying on a lightness-darkness dimension. In the last experiment, subjects matched the brightness of two peripheral squares, one attended and one unattended. When the stimulus appeared on a white background (Experiments 1, 2, and 4a) it was judged as brighter when attention was directed to its location than when attention was diverted to another location. When the stimulus appeared on a dark background (Experiments 3 and 4b), the opposite pattern of results was obtained: the attended stimulus was judged as darker than the unattended one. These results show that attention reduces the perceived contrast between the stimulus and its background, suggesting that attention enables subjects to provide a more veridical judgement of stimulus brightness by limiting processing resources to the square itself, at the expense of the surrounding background. As attention produced a directional brightness effect rather than just an improvement in report accuracy, the results can be attributed to early perceptual processing effects, hence providing support for early selection views of attention.


Ocean Science ◽  
2021 ◽  
Vol 17 (2) ◽  
pp. 579-591
Author(s):  
Di Wu ◽  
Guohong Fang ◽  
Zexun Wei ◽  
Xinmei Cui

Abstract. The Korea Strait (KS) is a major navigation passage linking the Japan Sea (JS) to the East China Sea and Yellow Sea. Almost all existing studies of the tides in the KS employed either data analysis or numerical modelling methods; thus, theoretical research is lacking. In this paper, we idealize the KS–JS basin as four connected uniform-depth rectangular areas and establish a theoretical model for the tides in the KS and JS using the extended Taylor method. The model-produced K1 and M2 tides are consistent with the satellite altimeter and tidal gauge observations, especially for the locations of the amphidromic points in the KS. The model solution provides the following insights into the tidal dynamics. The tidal system in each area can be decomposed into two oppositely travelling Kelvin waves and two families of Poincaré modes, with Kelvin waves dominating the tidal system. The incident Kelvin wave can be reflected at the connecting cross section, where abrupt increases in water depth and basin width occur from the KS to JS. At the connecting cross section, the reflected wave has a phase-lag increase relative to the incident wave of less than 180∘, causing the formation of amphidromic points in the KS. The above phase-lag increase depends on the angular velocity of the wave and becomes smaller as the angular velocity decreases. This dependence explains why the K1 amphidromic point is located farther away from the connecting cross section in comparison to the M2 amphidromic point.


2021 ◽  
Vol 12 (2) ◽  
pp. 146-155
Author(s):  
D. M. Malyutin

The development of wave solid-state gyroscopes (VTG) is one of the promising areas of development of gyroscopic angular velocity sensors. VTG from the standpoint of manufacturing technology, tuning and control systems, as well as accuracy characteristics, has a number of advantages compared to other types of gyroscopes. When developing VTG, they strive to reduce the gyroscope's own care, zero signal bias, and the non-linearity of the scale factor in the operating temperature range However, when creating the device, due attention is often not paid to the existing opportunities to improve the dynamic accuracy of the gyroscope by developing promising structural solutions for building control circuits and information processing. The solution to this problem was the goal of the work.Using the methods of the theory of automatic control, the dynamics of a wave solid-state gyroscope with a metal resonator and piezoelectric elements in the closed-loop mode of Сoriolis acceleration compensation are studied. Piezoelectric elements perform the functions of displacement and force sensors.Two promising structural solutions for constructing VTG control and information processing circuits are proposed and considered. Relations are established for selecting the parameters of the links of these contours, which provide an increase in the dynamic accuracy of the gyroscope. In the first case, the proposed structure for constructing the VTG allows us to significantly reduce the dynamic errors caused by the difference in the scale coefficient of the VTG at different frequencies of the measured angular velocity in the bandwidth. Such a structure for constructing a VTG can be recommended when solving a measurement problem in which it is necessary to accurately measure the angular velocity, and the phase lag of the output signal in relation to the measured angular velocity is of secondary importance. In the second case, the proposed structure of the VTG construction corresponds to the transfer function of the relative measurement error with secondorder astatism, and the absolute measurement error in the frequency band of 10 Hz does not exceed 0.1 %.


1966 ◽  
Vol 25 ◽  
pp. 323-325 ◽  
Author(s):  
B. Garfinkel

The paper extends the known solution of the Main Problem to include the effects of the higher spherical harmonics of the geopotential. The von Zeipel method is used to calculate the secular variations of orderJmand the long-periodic variations of ordersJm/J2andnJm,λ/ω. HereJmandJm,λare the coefficients of the zonal and the tesseral harmonics respectively, withJm,0=Jm, andωis the angular velocity of the Earth's rotation. With the aid of the theory of spherical harmonics the results are expressed in a most compact form.


Author(s):  
T. Oikawa ◽  
M. Inoue ◽  
T. Honda ◽  
Y. Kokubo

EELS allows us to make analysis of light elements such as hydrogen to heavy elements of microareas on the specimen. In energy loss spectra, however, elemental signals ride on a high background; therefore, the signal/background (S/B) ratio is very low in EELS. A technique which collects the center beam axial-symmetrically in the scattering angle is generally used to obtain high total intensity. However, the technique collects high background intensity together with elemental signals; therefore, the technique does not improve the S/B ratio. This report presents the experimental results of the S/B ratio measured as a function of the scattering angle and shows the possibility of the S/B ratio being improved in the high scattering angle range.Energy loss spectra have been measured using a JEM-200CX TEM with an energy analyzer ASEA3 at 200 kV.Fig.l shows a typical K-shell electron excitation edge riding on background in an energy loss spectrum.


Author(s):  
Frances M. Ross ◽  
Peter C. Searson

Porous semiconductors represent a relatively new class of materials formed by the selective etching of a single or polycrystalline substrate. Although porous silicon has received considerable attention due to its novel optical properties1, porous layers can be formed in other semiconductors such as GaAs and GaP. These materials are characterised by very high surface area and by electrical, optical and chemical properties that may differ considerably from bulk. The properties depend on the pore morphology, which can be controlled by adjusting the processing conditions and the dopant concentration. A number of novel structures can be fabricated using selective etching. For example, self-supporting membranes can be made by growing pores through a wafer, films with modulated pore structure can be fabricated by varying the applied potential during growth, composite structures can be prepared by depositing a second phase into the pores and silicon-on-insulator structures can be formed by oxidising a buried porous layer. In all these applications the ability to grow nanostructures controllably is critical.


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