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Our brain usually tries to avoid emptiness, monotony, and an aggressive visual environment. The visual system highlights certain areas of the surrounding scene and controls the eye to recognize their details. The angle of view of a clear vision is about 2° of the visual field, and the oculomotor (oculomotor) muscles constantly make various movements to search for small objects. These movements allow you to direct the view in such a way that the visual stimulus is projected onto the central fossa, since this part of the retina is characterized by the most acute vision. Our eyes can both be fixed on the object and move continuously. Consider some publications in this area that describe the main types of eye movement.

The article of [Butenko, 2016] presents a brief description of types of eye movements and analyzes the methods and systems registering the oculomotor activity. The movement of the eyes is the natural component of visual perception. The eyes make micromovements even in the case of relative fixity of look. It is generally known that there are eight types of eye movements which belong to the micro- and macromovements.

The macro eye movements characterize the change of eye direction and can be controlled. They are divided into macrosaccades (sudden change of eye direction), accompanying movements (the sweeping drift of gaze after the moving fixation object), vergence eye movements (coupling and decoupling of visual axes), nystagmus (vibratory eye movements together with the accompanying movements) and torsional movements (rolling eye movements about the visual axis). The micro eye movements are the natural background of oculomotor activity that cannot be controlled. The micro eye movements are divided into the tremor (frequent eye vibrations), drift (sweeping drift of gaze interrupted by the micro jumps) and microsaccades (rapid eye movement occurring in the case of fixation points change).

Oculography (eye tracking) is a determination of eye position and meeting point of the eye bulb optical axis with the plane of observable object. The eye tracker is a device used to determine the orientation of the eye bulb optical axis in space. The eye trackers are applied in the course of study of the visual system as well as in psychology and cognitive linguistics.

The tracking methods can be divided into two groups: contact and noncontact. The first group is represented by the electro-oculography, photooptic and electromagnetic methods. The second group includes the photoelectric method and video recording.

The electromagnetic method is based on the change of equivalent stress in which any eye movement is transferred. The inductive emitter is fixed with the sucking cup (contact lens) on the eye bulb, and the receiver coils are placed around the head. The emitter establishes the alternating electromagnetic field in the receiver coils. The moving of emitter results in the change of electromagnetic field strength. Furthermore, the signal is amplified being transmitted to the input of recording oscillographs.

The photooptic method is based on the recording of reflected light when the sucking cup with the miniature mirror from which the narrow beam of light is reflected and fallen on the input of light-beam photographic recorder is set on the eye bulb. The photooptic method allows the analysis of the microformation of oculomotor activity.

Electrooculography. The measurement of potential differences in the tissues adjacent to the eyehole is a basis of electrooculography. The eye movements are recorded by means of electrodes set around the eye pits. The potential marker points at the gaze direction, and the variation value of potential difference indicates the rotation angle.

The photoelectric method is based on the transformation of infrared light beam reflected from the cornea into the electric signal. The amount of reflected light is changed in the course of eyes moving, and the photocurrent value is changed respectively.

Video recording. The video recording method embraces two interdependent procedures – the video recording of eyes of the test person and programmed determination of eye direction on each frame of video sequence. The pupil edge or center, sclera blood vessels or corneal speck is a source of information about the eye direction. The other kind of video recording method intends the eye lightening with the point source of infrared light and high-speed shooting by infrared video camera. This method is used in the devices produced by Tobii Company. Such eye tracking devices embrace: Tobii REX, Tobii EyeX, Tobii TheEyeTribe [Website tobii.com, 2020].

Let’s consider some current articles concerned with the study of oculomotor activity. The work of [Wegner-Clemens et al., 2017] is dedicated to the study of gaze fixation in the course of the viewing of faces. Although the human face features many visual peculiarities, observers prefer to fix their eyes mainly on the eyes and mouth. It is more explained by the evolution of social signs of recognition and human society communication.

The experimental findings of 41 participants looking at four faces with different starting stimuli were represented (Figure 1.2.5). The blue ellipses on the face show the position of each particular eye fixation, and the size of every ellipse is proportional to the fixational pause. The degree of eye fixation on the face from the left side (Figure 1.2.5) is presented in the form of thermal map. The degree of eye fixation on the faces is a useful tool to evaluate the individual differences and subsequent recommendations for social communication.

The article of [Ito et al., 2017] provides a new method to analyze the eye movements during the natural viewing. The method is based on the fact that eyes move from and to the objects of the visual scene. The method was used experimentally for two macaques freely looking at the visual stimuli in the form of scenes. The analysis revealed that monkeys had a behavioral shift from the free viewing to the focal processing of visual stimulus.

Figure 1.2.5 Comparison of methods for determination of regions of interest and principal component analysis [Wegner-Clemens et al., 2017].

The work of [Barabanschikov et al., 2010] analyzes the definition of oculomotor activity and expressions perception depending on the space orientation of the face. It is demonstrated that 180° rotation of face image results in the declining of efficiency of recognition of emotions intensity. The weak expressions of the face on the reversed image are perceived as the calm state. This process depends on the emotions modality and has the complex nonlinear nature. The “fear” and “grief” are identified worst of all, and the calm face expression – better and more stable. If increasing the intensity of emotions of the face on the direct-viewing image the effect of left-sided dominance is registered, and in case of reversed image the effect size is increased (Figure 1.2.6). However, the dominance of perceiving of feebly marked expressions has a right-sided nature.

The work of [Basyul et al., 2017] is dedicated to the study of oculomotor activity in case of face recognition. Thirty-two persons of Tuvan nationality who evaluated the likeliness of goal objects presented in pairs by means of a five-grade scale took part in the experiment. The goal pairs of photos with human faces which were coupled by means of two original photos (Caucasoid and Asian type) and four intermediate photos were used as the stimulus material. They were made with the help of morphing in increments of 20% (Figure 1.2.7). The oculomotor activity of test subjects was registered by means of eye tracker EyeTribe in the course of stimulus material presenting. The actuality of research is determined by the questions of maintenance of public security and business communication.

Let’s consider the main types of micro- and macromovements of human eye used by us in everyday life.

Saccades. The most frequent eye movement is the saccade (French, saccader – tugging). A saccade is a tear-off, discontinuous movement of the eyes, with a quick transfer of gaze from one object to another. Saccades can be small (less than 3° fields of view) and large (about 40°). Macro saccade occurs when abrupt changes in the position of the eye are performed with high speed and accuracy. Usually the frequency, angular velocity and direction of gaze are determined by the nervous system in advance. In order to avoid undesirable effects, saccadic movements are performed extremely quickly. Muscles performing saccadic movements are among the fastest muscles in the body. Usually the number of saccades is up to 3 times per second. Saccades can be reflex and controllable, and they are also performed in a state with closed eyes.

Figure 1.2.6 Examples of oculograms of different test subjects who perceive the expressions of face on the direct-viewing and reversed images [Barabanschikov et al., 2010].

Figure 1.2.7 Transition row of face images from which the goal stimulus pairs are formed [Basyul et al., 2017].

Saccades are used primarily for examination and study of the visual field. They are especially important when performing such visual tasks as reading or viewing paintings, photographs, and portraits (Figure 1.2.8, 1.2.9). Eye movements when viewing an image ensure that its various parts get into the zone of the central fossa, which makes it possible to examine the details. The points at which the gaze is fixed are not accidental. These are the most informative places of the image, the places where the most important signs are located. For example, when scanning a face in a photograph, the set of fixation points falls on the areas where the eyes, nose and mouth are located.

It is well known that the algorithm for eye movement during reading is intermittent. While reading, the eyes perform a series of saccades alternating with pauses, fixations, and some return movements (repressions). The reading process itself takes place precisely during fixations; with saccadic movements, the vision is functionally blocked.

Figure 1.2.8 Schemes of eye movement when viewing various images [Yarbus, 1967].

Figure 1.2.9 A reproduction of the painting “Didn’t Wait” by Russian artist I. Repin [Repin, 2020], was used to determine oculomotor activity (right) [Yarbus, 1967].

The reader seeks to fix the view on the most meaningful fragments of the text; as a rule the word is the object of fixation. When reading, we can recognize an average of 4-5 letters to the left of the fixation point and 8-11 to the right with normal font sizes. The spaces between the words play the role of visual design; they are crucial for the algorithm of eye movements. Reading speed significantly decreases with no gaps. Try to read the text typed without spaces, presented in Figure 1.2.10. This will require fixing the gaze on each letter, but if you continue the reading process, then addiction will occur; the eye will perform shorter saccades, and the reading comfort will increase.

Eye tracking. Tracking eye movements are a reflex, and occur when tracking a moving stimulus. Unlike saccades, these movements are smooth and slow. Usually the speed of tracking movements is determined by the speed of movement of the stimulus; this ensures the stabilization of the image on the retina.

Vestibulo – ocular movements. When we change the position of the head and body in space, we continue to perceive our surroundings in a stable way. This is achieved through compensatory movements of the eyeballs,

Figure 1.2.10 Text without spaces between words.

which allow you to maintain a stable image. These movements are reflex vestibulo – ocular movements. Eye movements are stimulated by the vestibular apparatus of the middle ear, where the sensory system is located to determine the location of the body in space. During physical activity, the eyes perform precise movements, compensating for both body movements and head movements.

Vergent eye movements. Sometimes there is a need for coordinated movements of both eyes; these movements are called vergent. Vergent movements move the eyes horizontally in opposite directions in such a way that the mixing and dilution of the visual axes (convergence and divergence) occurs. This allows both eyes to focus on the same object. Such eye movements are characteristic of primates, in which the frontal position of the eyes and the field of view has a binocular overlap. Vergent movements can be observed when the reduction of a glance at the tip of one’s own nose is required.

Eye micromovements. When you fix the look at the stimulus, you can observe a number of reflex movements, which are called micromovements of the eyes (tremor). As a result of micromovements, the axis of the eye describes a closed figure in the form of an ellipse. This is the natural motor background of the activity of oculomotor muscles, which is not consciously controlled. With the help of special devices you can register these micromovements of the eyes. In the process of fixing the eyes are in constant motion, if you completely exclude involuntary, small movements of the eyes, the image of the stimulus on the retina begins to blur and disappear.

Mixed movements. The visual perception of the environment usually occurs through a combination of different types of eye movements; they are mixed movements. For example, observation of a moving object requires both smooth tracking movements and saccadic and vergent movements.

Effective eye movements are achieved at a certain level of development of oculomotor muscles. In children of 4–5 years of age, eye movements are different from those of adults, so their vision is less effective; it is difficult for them to fix their gaze on a particular object. When they were asked to fix their gaze on a small, bright, stationary object in a dark room, their line of sight scanned the area 100 times larger than in adults. Children do not predict changes in the direction of movement of the object; these movements are formed gradually on the basis of practice.

It should be noted that the concept of tracking is used to control attention when designing advertising, when the eye of the observer is directed to a certain part of the visual field. In web design, F-pattern-based navigation is highlighted (Figure 1.2.11). As you read consecutive lines, the number of commits decreases, and their duration also decreases for any length of line and any line spacing. The movement of our gaze usually covers the right side of the visual field, narrowing as the gaze moves down the text. Our attention avoids non-informative images consisting of small homogeneous elements; they can cause unpleasant sensations and illusions.

Figure 1.2.11 F-Pattern navigation.

Figure 1.2.12 Comparison of certainty value of web page and saccadic estimation, (a) web pages, (b) thermal map of eye fixation [Xia, Quan, 2020].

The work of [Xia, Quan, 2020] reports the studies on the modeling of users’ attention looking through web pages. The saccadic search model of dynamic visual behavior of people is offered in the work. The multilevel analysis of signs of visual information and definition of probability of user eye fixation are used. The experimental results concerning the eye tracking in the course of free web pages viewing showed the efficiency of the offered method (Figure 1.2.12).