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,
