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Exaggeration of sharp corners. Encyclopedia of visual illusions

At leisure / Visual (optical) illusions

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Many illusions are explained by the ability of our vision to exaggerate the sharp corners that we see on flat figures. Firstly, perhaps this kind of illusion appears due to the phenomenon of irradiation, as the light space we see expands around the dark lines that limit the acute angle. Secondly, it is also possible that an acute angle increases due to a general psychological contrast, since often acute angles lie next to obtuse ones, and the situation has an influence. Thirdly, the direction of eye movement and their mobility in general is of great importance for the emergence of these illusions. If there is a break in the lines, then our eye first of all "grabs" an acute angle, since the axis of the field of view moves first along the shortest direction and only then examines the sides of obtuse angles.

The fact that this illusion really depends on the movement of the eyes is confirmed by the fact that when the field of view is illuminated with short-term flashes, many of the illusions of this kind are not observed, since the eye does not have time to move during the flash to view both sharp and obtuse angles of the figure.

In architecture, in particular, in order to avoid the illusion of curvature of truly parallel lines intersected by lines that form sharp and obtuse angles with the first, a special breakdown of parts is used and preference is given to radial lines.

A person changes the direction of movement of his eyes with a certain effort, and therefore special methods are used in architecture to gradually slow down the movement of the eyes before they should change the direction of Movement. The best example of this is the capitals and bases of the columns, which retard the movement of our gaze from the bottom up and, conversely, from the top down along the shaft of the columns. Finally, in some cases, the apparent sharp corners may be exaggerated due to astigmatism of the eye. In any case, sharp corners always seem to us larger than they really are, and therefore certain distortions appear in the true ratio of the parts of the visible figure. Here are some visual illusions that arise from the overestimation of sharp corners (Fig. 63-70). On fig. 65-67 the simplest illusions are presented, due to the exaggeration of sharp corners.

Rice. 63. Segments of straight lines that intersect parallels at acute angles appear to be offset and either do not belong to the same lines (left and center) or are not sides of the same angle (right). (Poggendorff illusion.)

Rice. 64. It seems that when continuing, the left arcs will not converge with the right ones, in fact they converge. This kind of illusion can often be seen in buildings that have vaulted ceilings, doors or windows. It seems that the lines of the vault, dissected by the standing column in front, do not converge

Rice. 65. The straight line ab seems to be broken at the point O, and at the top the angle aOb seems to be less than 180 °, and at the bottom it is more than 180 °

Rice. 66. Are segments A and B, as well as segments C and D, continuation of one another

Rice. 67. Each subsequent increase in the angle seems to be larger than the previous one, although in all cases the difference is 5 °

When we look at two lines separated by a gap, we are able to connect them "in our mind" and determine whether one of them is a continuation of the other or not. If, however, we draw another to one of these lines so that they form an acute angle, the confidence in our assessment will immediately disappear. For example, in fig. 66 the continuation of A seems to be below line 5, and the continuation of C seems to be to the right of D. To make the illusion disappear, line C or A must be closed. 22 and 24. Note that the illusion disappears if we choose a different position of observation, that is, the appearance of the illusion depends on the "point of view" on the given object. So, if in Fig. 68, 69 and 70 look along parallel lines, combining the plane of the picture with the direction of view, then the illusion will disappear. The illusion may not be observed if the conditions of observation do not favor it. Therefore, sometimes we can see what we fail to see in other surroundings.

Rice. 68. Parallel straight lines due to the influence of the background appear non-parallel and curved.

Rice. 69. Parallel straight lines due to the influence of the background appear non-parallel and curved.

Rice. 70. Parallel straight lines due to the influence of the background appear non-parallel and curved.

This principle is based on the examination of the so-called "mysterious pictures" and the reading of "mysterious inscriptions". These pictures are drawn by deliberately increasing the vertical length of objects and greatly reducing the horizontal one, and the inscriptions are written so that they consist of letters deliberately stretched in height and narrow in the horizontal direction (Fig. 71). Combining the plane of the sheet with the plane of the eyes, we reduce the visible vertical dimensions of the letters and freely read this "mysterious inscription".

Rice. 71. Read an Arabic proverb

It turns out that if the figures in Fig. 68, 69 and 70 are viewed with a brief flash of light, then the illusion disappears.

It should be noted that sometimes a change in the direction of the lines and a distortion of the shape of the figure also occurs from the fact that the eye follows the directions of other lines in the field of view. Thus, there may be cases of a combination of causes that cause the illusion of vision, for example, exaggeration of sharp corners and psychological contrast, or one of the indicated circumstances, and the fact that the gaze, when viewing a figure, slides along the background lines surrounding it (Fig. 72-78) *.

* (The illusion of Figs. 75, 76 was first pointed out by Privatdozent of Moscow University P. V. Preobrazhensky.)

Rice. 72. The middle parts of the lines of this figure are parallel, but seem to be non-parallel.

Rice. 73. The rectilinear sides of the square seem to be curved, and the whole square - deformed

Rice. 74. The sides of a square and straight lines seem curved, non-parallel

Rice. 75. The upper right corner of the square does not seem straight, but sharp

Rice. 76. Circle looks like an oval

Rice. 77. The circle appears to be an oval, symmetrical about the angle bisector

Rice. 78. Intentional curvature of straight lines fig. 74 may give the impression that a regular square and parallel lines are drawn against the background of concentric circles (the illusion will disappear)

It should be noted that the vast majority of the illusions of vision given by us in paragraphs 4, 5 and 6 can, if desired, be eliminated by the appropriate representation of lines and figures in those drawings and drawings where these illusions may appear. For example, all those segments in Fig. 21-45, which seem large to us, can be deliberately depicted as smaller; curves, angles, circles that seem smaller can be intentionally enlarged; straight lines that appear crooked can be drawn as curves so that they appear straight, and so on (Fig. 78). These opportunities are widely used by artists, as L. Euler pointed out as far back as 1774, who wrote: “Painters are most able to turn this general and akin to all deceit in favor,” and further explained: “On this deceit, all pictorial art is based. we are accustomed to judging things by the very truth, then this art could not have a place, as well as when we were blind.

As mentioned earlier, architects are also very often faced with the need to correct the erroneous visual impression created by certain parts of structures. Already the architects of Ancient Greece deliberately introduced appropriate corrections (corrections) of the apparent curvature resulting from visual illusions when observing elements located much higher than the horizon. Similar corrections were made in 1764 during the construction of a portico in the building of the Soufflot Pantheon in Paris.

Illusions based on our ability to assimilate (figs. 45-50) are more difficult to eliminate, but in this case we can avoid optical illusions using such simple devices as a ruler and compasses.

In rare cases, it is not advisable to eliminate the illusion, for example, in the case of a typographic font (Fig. 58).

Author: Artamonov I.D.

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