work of [Gonzalez, Niechwiej-Szwedo, 2016] describes the influence of monocular vision on the accuracy of coordination of hand movements at the moment of capture. It’s known that the moveable eyes are in motion up to the completion of the movement. The eyes moving to object is analyzed in the space and recognized thus simplifying the control of subsequent movements. However, the monocular vision doesn’t allow the complete determination of the position of the object and hands in the space. Fifteen people who carry out the control action using the video tracker and system of motion capture took part in the experiment. As a result the time for taking the bead and pulling it on the needle at the monocular vision was increased up to 2.5 sec, and in case of binocular vision it was 2 sec. The obtained results prove the defining role of binocular vision in the everyday living of man.
The work of [Luke, Henderson, 2016] considers the influence of significance of visual stimulus content on eye movement. The text, photos of townscapes, landscape pictures and their analogs such as stylized pseudo stimuli were used as the visual stimuli. As a result it was determined that the duration of fixation and saccades amplitude were larger for pseudo stimuli as they need more time to be recognized and perceived.
Linear perspective. In the perception of the depth of space, linear perspective plays an important role. Linear perspective provides for a gradual decrease in the magnitude of distant objects and distances between them. The most obvious example of a linear perspective is railroad rails (Figure 1.4.2) [Website istockphoto, 2020]. Despite the parallelism, it seems that the rails in the distance converge at a point called the vanishing point.
Figure 1.4.2 Linear perspective.
1.4.2 Monocular Motion Parallax
Monocular motion parallax (from the Greek word paralaxis – change) is a monocular source of information about the depth and relative position of objects in view, resulting from the movement of an observer or objects. When the observer fixes his gaze on some point of the field of view, and at this time he moves, it begins to seem to him that objects lying closer to the fixation point move faster than more distant objects. During the movement of the head, the images of objects in remote locations on the retina will be mixed at different distances. It seems to the observer that more closely spaced objects move in the direction opposite to the direction of eye movement, and more distant objects move in the same direction [Shiffman, 2008], [Abbasov, 2019].
1.4.3 Binocular Signs
For the perception of primary visual information, monocular signs of space play an important role. However, to accurately determine the depth of space requires the activity of both eyes. Binocular signs are spatial information that can only be obtained by perceiving the surroundings with both eyes.
Binocular disparity. Animals with a frontal arrangement of eyes (predators, primates) see a large part of the visual field with both eyes. Within the area of binocular overlap, two eyes receive slightly different images of the same three-dimensional visual information. The field of view of one eye is somewhat different from the field of view of the other. This difference between the two retinal images is called binocular disparity (binocular parallax). Disparity is strongly pronounced for closely located objects, and decreases as they are removed. After four meters, the difference between retinal images becomes insignificant, and binocular disparity weakens.
1.4.4 Binocular Disparity and Stereopsis
Due to the binocular disparity of the images on the retina of both eyes, there arises a special perception of the depth of space and volume, which is called stereoscopic vision, or stereopsis (from the Greek Stereos – volumetric and opsis – vision) [Luria, 2006], [Shiffman, 2008], [Abbasov, 2016]. One of the most impressive examples of stereoscopic vision is the perception of the effect of depth when viewing slides with a stereoscope, that is, when presenting each eye with slightly different planar images of the same scene, called stereograms, the illusion of volume.
Stereograms can also be created with a random set of black and white elements. Meaningful perception of the depth of these stereograms is possible only after the two images are combined in a certain central visual zone. When viewed with a monocular, these images lose depth and are perceived as uniformly arranged random elements. A special form of a stereogram containing two combined patterns for both eyes is called an autostereogram. An autostereogram is an unusual and difficult task for the visual system, since it is necessary to focus the eyes at a distance different from the one on which the drawing itself is located. But if you look with two eyes and do not suffer from stereo-blindness, then with a certain training session (and patience) you can see the stereoscopic image.
1.5 Visual Illusions
Illusion is a false or distorted perception of a phenomenon. Visual (optical) illusions arise when the visual perception does not correspond to the physical, real properties of an external stimulus. Illusions can be considered distorted perception of the surrounding reality, and thus differ from hallucinations, which are a false perception that occurs in the absence of external conditionality. According to the mechanism of occurrence, visual illusions can be divided into the following types:
– arising from the imperfection of the optical properties of the eye;
– resulting from the action of the entire visual system, including the brain;
– dynamic illusions arising from a change in the position of the stimulus in space or in time.
The survey of [King et al., 2017] is dedicated to the analysis of distortions of perceiving the visual illusions in case of confusional insanity. People suffering from confusional insanity may experience the anomalies at the different stages of processing of visual information. Generally, such people are unperceptive to the illusions of high level. Moreover, they may be influenced by some illusions of initial stage.
Let’s consider the illusion of “Hollow mask” [Website youtube.com, 2020] taken as an example. The mask is turned both clockwise and counterclockwise upon view (the successive steps are shown in Figure 1.5.1). In fact, the mask is turned one way. However, for the majority of observers the mask changes the direction of movement at some point of time. At the start of movement the convex front side of the mask doesn’t make a difficulty for the visual system and consciousness. When the mask begins to move toward the back side (the backing may be observed through the hollow eye pits) our brain turns it out because the convex side is more familiar for us. We didn’t use to see people with concave faces. In the course of further turning the brain turns out and restores the usual convex form of the mask at the crossing line once again. However, the brain of scizophrene cannot be deceived; that’s why the mask is still hollow for it after turning.
Figure 1.5.1 Sequenced frames of illusion of ‘Hollow mask’ [Website youtube.com, 2020].
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