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).
1.2.4 Effects of Masking and Aftereffects
If visual stimuli occur in close sequence from each other (in time or in space), they can overlap each other and mask the perception of each other. The cause of the masking effect is the inertia of vision due to the slowness of the neural response to the stimulation, as a result of which the response to the stimulus can be maintained even after its disappearance.
During saccades, the flow of visual information stops
