Features of oculomotor activity (eye movement) in patients with schizophrenia in recognizing essential signs using the example of the "Exclusion of the 4th superfluous" technique

Isaeva Elena Rudol'fovna ORCID: 0000-0002-7731-7693 Doctor of Psychology Professor, Head of the Department of General and Clinical Psychology, FSBEI HE I.P. Pavlov SPbSMU MOH Russia 197022, Russia, Saint Petersburg, L.Tolstogo str., 6-8 isajeva@yandex.ru Mukhitova Yuliana Vladimirovna ORCID: 0000-0003-4172-6257 PhD in Psychology Associate Professor, Department of General and Clinical Psychology, First St. Petersburg State Medical University named after Academician I.P. Pavlov 197022, Russia, Saint Petersburg, 6/8 Lva Tolstogo str. che88@mail.ru

Dmitriev Pavel Ivanovich ORCID: 0009-0000-1691-2838 PhD in Technical Science Head of Department of video Analytics of LLC "NPP Videomix", 197342, Russia, Saint Petersburg, trans. Krasnogvardeisky, 15 liter p, office of NPP Videomix LLC dmitriev@prointech.ru

Relevance

In the history of the study of schizophrenia, a special place has always been occupied by research in the cognitive sphere (Polyakov Yu.F., 1972; Kabanov M.M., 1985; Zotov M.V., 1998; Gurovich I.Ya., Shmukler A.B., Magomedova, 2001; Zeigarnik B.V., 2005; M. M. Kutz, I. C. Selter, I. K. Ferrnand et al, 2005; Abramov, V.A., Putyatin, G.G., Abramov, A.V., 2008; Ivanov M.V., Neznanov N.G., 2008; Bleicher V.M., Kruk I.V., Bokov S.N., 2009; Litvintsev S.V., Ershov B.B., Kolchev A.I., Kolchev S.A., 2010; Sarkisyan G.R., Gurovich I.Ya, Kif R.S., 2010; Cherednikova T.V., 2009; Cherednikova T.V., 2011; Gorkova I.A., 2011; Kritskaya, V. P., Meleshko T.K., 2015, etc.; Isaeva E.R., Lebedeva G.G., 2016; Plotnikov V. V., Plotnikov D. V., 2018, etc.; Mukhitova Yu.V., Isaeva E.R., Tregubenko I.A., Shoshina I.I., Hanko A.V., Limankin O.V., 2021) One of the first drew attention to the change in the sphere of perception of patients with schizophrenia V. A. Gilyarovsky (1941), who argued that that the cognitive activity of patients with schizophrenia is undergoing changes, starting from the primary links, ending with more highly organized processes.

Significant progress in understanding the mechanisms of the pathology of thinking was made thanks to B.V. Zeigarnik – she attached special importance to the pathopsychological method in the study of thinking disorders. The initial position of Soviet pathopsychologists (Kritskaya V. P., Meleshko T. K., Polyakov Yu. F., 1994; S. Ya. Rubinstein, 2004; B. V. Zeigarnik, 2005; Yu. F. Polyakov, 1973, 1978) was the understanding of the process of thinking as a reflexively conditioned activity formed in the process of ontogenesis (Bleicher V.M., 2009). Kritskaya V.P., Meleshko T.K., Polyakov Yu.F. (1994) in their works pointed to a violation of the selectivity of thinking due to a violation of the probabilistic structure of past experience and a weakening of its influence on actual mental activity.  When solving mental tasks (generalization, comparison, classification), patients with schizophrenia use both essential and latent signs with an equal degree of probability and significance. Distortion of the generalization process and violation of the selectivity of thinking, as end-to-end features of the psyche of patients with schizophrenia, are manifested in all intellectual activity (Kritskaya V.P., Meleshko T.K., Polyakov Yu.F., 2004; Kritskaya V.P., Meleshko T.K., 2015). A.I. Molochek pointed out the great importance of having an adynamic past experience and preservation knowledge itself (Bleicher V.M., 2009). Frumkin Ya.P. and Livshits S.M. (1979), in turn, also noted the participation of past experience in the formation of the clinical picture, while special importance was attached to the mechanisms of pathological revival of trace reactions. L.S. Vygotsky considered the manifestations of a decrease in the level of conceptual thinking in schizophrenia to the level of specific semantic formations, which, in his opinion, there is a change in the meanings of words (Zeigarnik B.V., 2005).

In the study of schizophrenia, research on neurocognitive, psycho- and neuro-linguistic aspects of cognitive impairment (neurocognitive deficit) is becoming increasingly relevant and important, which are considered as one of the leading components in the symptoms of schizophrenia in its diagnosis (Zotov M.V., 1999; Velligan D. I, 1999; M. F. Green, R. S. Kern, D. L. Braff, J. Mintz, 2000; Gurovich I.Ya., Shmukler A.B., Magomedova M.V., 2001; Kim C. K., Kim S. H., Choe B. M, 2004; Nuechterlein K. H., Dawson M. E., Green, M. F., 2006; S. Van Hooren, 2008; Ivanov M.V., Neznanov N.G., 2008; Isaeva, E. R., Tregubenko, I. A., Mukhitova, Yu. V., & Shoshina, I. I., 2021). Also, special attention is paid to the search for the brain mechanisms of these disorders. For example, E.R. Isaeva, Yu.V. Mukhitova et al. (2018) noted that violations of cognitive processes are detected even at the level of early processing of visual information.

The study of cognitive, including mental activity in schizophrenia requires the search and application of new approaches and diagnostic methods based on high information and medical technologies that can provide greater objectivity and reliability in research of thinking disorders. Using the eye tracker method, it becomes possible to analyze eye movement patterns in more detail in the process of solving a cognitive problem in patients with schizophrenia, which is important for understanding the structure and mechanisms of sensory-cognitive disorders in schizophrenia and for developing technologies for objective diagnosis of perceptual and thinking disorders. The AI tracker method allows you to answer questions about how a person processes visual stimuli and uses the information received to find a successful strategy for solving certain tasks. Given that the decision-making process is often hidden, unconscious, the ability to approach an understanding of this process through gaze tracking is potentially an important and promising research technology in terms of solving many theoretical and practical issues to determine the mechanisms of cognitive impairment, as well as to identify reliable diagnostic biomarkers. In this study, an attempt was made to objectify the assessment of cognitive processes based on the registration of eye movements (oculomotor activity) when solving mental tasks in patients with schizophrenia.

One of the main ways to get information about the outside world is vision. In humans, visual acuity decreases gradually from the central to the peripheral field of vision, therefore, in order to obtain accurate visual information, it is necessary to bring the image of a visual object to the zone of the clearest visual perception. Eye movements play an important role in this process: oculomotor activity ensures the receipt, transformation and further use of visual information obtained through the visual apparatus (Yarbus A. L., 1965; Drummers V. A., 1997; Ananyeva K. I., Drummers V. A., Kharitonov A. N., 2010; Drummers V. A., Zhegallo A.V., 2014).

It is noteworthy that eye movements give an idea of a person's homeostatic balance and reflect the decision-making process. Consequently, the science of vision explores the quality of the observed environment, determined under various experimental conditions. Moreover, it answers questions about how a person processes visual stimuli and uses the information received for a successful strategy to achieve certain goals (Yarbus A. L., 1965; Drummers V. A., 1997; Ananyeva K. I., Drummers V. A., Kharitonov A. N., 2010; Drummers V. A., Zhegallo A.V., 2014). Considering that approximately 95% of human decision-making occurs at the unconscious level (Zaltman, G., 2003; Pop, N., Al, Dabija, D.C., and Iorga, A.M., 2014; Nyoni, T., and Bonga, W. G., 2017), the study of cognitive processes using gaze tracking opens up the ability to approach the invisible part of neural connections, overcoming the limitations associated with the subjectivity of conducted techniques based on self-reflection and self-observation: questionnaires, tests (Connors, B. L., Rende, R., and Colton, T. J., 2016; Bell, L., Vogt, J., Willemse, C., Routledge, T., Butler, L. T., and Sakaki, M., 2018).

Theoretical models that reveal the interrelationships of patterns of gaze movement and cognitive processes seem insufficient at the moment. In addition, following the global trend of the so–called "digital strategy", technologies are needed to identify cognitive impairment in solving problems of primary and differential diagnosis, as well as to monitor the mental state and functioning of a person (Bryson G. B., 2001; Bestelmeyer P. E. G., Tatler B. W., Phillips L. H., Fraser G., Benson P. J., Clair St, 2006; Morita K., Miura K., Fujimoto M, 2017; Thakkar K. N., Diwadkar V. A., Rolfs M., 2017; Scholl, J., and Klein-Fl?gge, M., 2018; Rutkowski, T. M., Abe, M. S., Koculak, M., and Otake-Matsuura, M., 2020).

AI tracking is considered a promising approach to enhance the assessment of the reliability of the results and objectification of this process. Studies have established that oculomotor activity is a reliable biomarker of both conscious and unconscious cognitive processes. For example, the characteristics of oculomotor reactions make it possible to differentiate the reliability of the answers received (cases of lies or unreliability in the answers of the subjects are distinguished). Research using an EYE tracker experimentally confirms that eye movement patterns serve as a quantitative (objective) characteristic of the process of perception, attention and thinking in real time. For example, according to the results of their research, P. Holzman and S. Levin suggested that the already well-known deficit of smooth tracking is associated with violations of involuntary attention, expressed in the form of disinhibited saccades. There is also a high frequency of short involuntary saccades characteristic of patients with schizophrenia, which confirms existing hypotheses about excessive distractibility to secondary, insignificant signs and the inability to filter information, cutting off more or less significant stimuli in conditions of a given activity (Yarbus A.L., 1965; Vladimirov A.D., 1972; Barabanshchikov V.A., 1997; Lee K. H, Williams L. M., 2000; Sereno, A. B., Holzman, P. S., 1993; Minassian A., Granholm E., Verney S., 2005; Kim, J., Park, S., and Blake, R., 2011; Ananyeva K. I., Drummers V. A., Kharitonov A. N., 2010; Domagalik et al., 2012; Drummers V. A., Zhegallo A.V., 2014; Daglas, R., Y?cel, M., Cotton, S., Allott, K., Hetrick, S., and Berk, M., 2015; Butenko V. V., 2016).

In recent years, many studies have been conducted to describe the characteristics of oculomotor activity in patients with various neuropsychiatric disorders in comparison with the norm. For example, Shiino T., Miura K., Fujimoto M. with co-authors, we revealed significantly significant differences in five characteristics of oculomotor activity in patients with autism spectrum disorders and patients with schizophrenia, in comparison with the normative group, in the tasks of "free viewing" and viewing with a given purpose (tests of smooth gaze following) (Shiino, T., Miura, K., Fujimoto, M., Kudo, N., Yamamori, H., Yasuda, Y., et al., 2020).

The experiment of D.A.Shvayko and E.A.Budenkova showed that the oculomotor reactions of people suffering from schizophrenia are characterized by a high degree of disorganization, the presence of incorrect saccades, prolonged fixation on isolated areas of stimulus material that do not contain information of primary importance for the task, compared with oculograms of healthy people (Tkachenko A. A., Demidova L. Yu., Babicheva N.. V., 2018). Dysfunctional eye movements indicate a violation of the smooth tracking system, which is reflected in an increase in indicators of various oculomotor characteristics (saccade frequency, duration of gaze fixation, etc.) in patients with schizophrenia, in comparison with the normative group. The increased frequency of saccades during gaze following in solving a cognitive task is probably compensatory, but this interpretation remains ambiguous due to the lack of data on certain types of saccades (Butenko V. V., 2016).

It has been described that cognitive impairments detected by gaze analysis can indicate or even predict mental illness (Fujioka, T., Inohara, K., Okamoto, Y., Masuya, Y., Ishitobi, M., Saito, D. N., et al., 2016; Almubark, I., Chang, L.-C., Shattuck, K. F., Nguyen, T., Turner, R. S., and Jiang, X, 2020; Wolf, A., Ueda, K., and Hirano, Y., 2021). In addition, gaze tracking can provide valuable information about cognitive processes in both healthy adults and patients with latent forms of disorders. Preliminary results of a number of studies show that the parameters of the gaze metric, such as: fixations (their location, number and duration), saccades (their number and amplitudes) and the length of the path scan are abnormal in a variety of neurological and mental diseases (Skripka E. Yu, 2011; Beedie, S. A., St.Clair, D. M., and Benson, P. J., 2011; Beedie S. A., Benson P. J., Giegling I., 2012; T?rkan, B. N., Amado, S., Ercan, E. S., and Per?inel, I., 2016; Morita K., Miura K., Fujimoto M., 2017; Tkachenko A. A., Demidova L. Yu., Babicheva N. V., 2018; Li, J., Zhong, Y., Han, J., Ouyang, G., Li, X., and Liu, H..,2020). Since many clinical studies require diagnosis based on etiology (i.e., understanding the processes of brain functioning in individuals suffering from mental disorders), the development of reliable biomarkers is the main goal of modern clinical research (Lee K. H, Williams L. M., 2000; Kim, J., Park, S., and Blake, R., 2011; Daglas, R., Y?cel, M., Cotton, S., Allott, K., Hetrick, S., and Berk, M., 2015; Yahata, N., Kasai, K., and Kawato, M., 2017; Wolf, A., Ueda, K., and Hirano, Y., 2021).

The purpose of the study: to determine the characteristics of oculomotor activity in patients with schizophrenia and in healthy respondents when solving a cognitive task of searching and choosing a common (unifying) feature with the definition of an unsuitable (superfluous) object on this basis.

Materials and methods of research During the study, 45 patients (26 men (56%), 19 women (44%), average age 39±11 years) were examined with a diagnosis of schizophrenia, paranoid form, on the basis of St. Petersburg State Medical Institution "Psychiatric Hospital No. 1 named after P.P. Kashchenko". The diagnosis was established in accordance with the criteria of ICD-10. The patients' participation in the study was voluntary, provided that there was no intellectual defect, active psychotic or other condition that prevented the ability to assess their condition. The control group included 59 healthy subjects (15 men (25%), 44 women (75%), average age 21±3 years). To assess the characteristics of oculomotor activity, the AI tracker method was used using a hardware and software complex for contactless registration of human oculomotor activity (camera frequency 250 Hz, accuracy 0.3?, camera operating distance 60-85 cm, capture area 32-42 cm from a distance of 70 cm, camera range 850 nm (NIR). To combine the points of view in the fixation, the standard I-DT (Dispersion Threshold Identification) algorithm with a fixation threshold of 70 ms was used. To assess the level of generalization and its disorders in the thinking of patients with schizophrenia, the “Exclusion of the fourth superfluous" technique was used. The calculation of mathematical and statistical data was performed in the STATISTICA 10 program using the following statistical analysis methods: descriptive statistics, frequency analysis, comparative analysis using the Mann-Whitney criterion.

The results of the study.

Patients with schizophrenia, when solving mental tasks using the "Exclusion of the 4th superfluous" method, demonstrate a higher frequency of fixations, in comparison with the normative group, on a visual stimulus (the frequency of fixations is higher than in the norm group; p<0.001), fixations are of a longer nature (average time and maximum time of fixations, p<0.001), which may indicate a longer examination of stimuli and difficulties in making a decision when choosing an extra item in the card. Patients with schizophrenia demonstrate a smaller pupil width diameter (p<0.001), which may indicate a low level of cognitive load during the period of solving an urgent task, difficulty in concentration and concentration, and this may also be a consequence of medication therapy (Table 1).

Table 1 Comparative analysis of the characteristics of oculomotor activity in patients with schizophrenia and in the normative group when solving mental tasks in the "Exclusion of the fourth superfluous" method

A comparative analysis of the characteristics of oculomotor activity in the normative group and in patients with schizophrenia was carried out when solving problems, depending on the level of generalization of the selected trait: by categorical and functional criteria, by specific situational criteria, latent criteria. The results showed statistically significant differences (p<0.01) in the number of visual fixations and the duration of fixations in all three response options: patients with schizophrenia spend significantly more time studying the visual stimulus and commit a greater number of fixations when choosing a feature for generalization (Table 2, Table 3, Table 4).

Table 2 Comparative analysis of the characteristics of oculomotor activity in patients with schizophrenia when generalized by categorical and functional characteristics when solving problems in the "Exclusion of the fourth superfluous" method

Table 3 Comparative analysis of the characteristics of oculomotor activity in patients with schizophrenia when generalized according to a specific situational feature in the "Exclusion of the fourth superfluous" method

Table 4 Comparative analysis of the characteristics of oculomotor activity in patients with schizophrenia when solving latent tasks in the "Exclusion of the fourth superfluous" method

Further, a comparative analysis of oculomotor activity in patients with schizophrenia was carried out when choosing the right answer, i.e. on an essential basis (categorical and functional, specifically situational), and an incorrect answer, i.e. on an insignificant basis (latent). Patients with schizophrenia, when solving the problem of choosing the wrong answer (latent sign), demonstrate fewer fixations and longer fixation time on stimulus images, compared with similar characteristics of oculomotor activity in patients with schizophrenia when choosing the right answers - according to categorical and specific situational signs (p<0.001) (Table 5, Table 6).

Table 5 Comparative analysis of the characteristics of oculomotor activity in patients with schizophrenia when generalized by specific situational and latent signs when solving problems in the "Exclusion of the fourth superfluous" method

Table 6 Comparative analysis of the characteristics of oculomotor activity in patients with schizophrenia when generalized by categorical and latent signs when solving problems in the "Exclusion of the fourth superfluous" method

Next, we analyzed the answers and features of the gaze movement when solving problems in simple difficulty cards. Patients with schizophrenia coped with them more easily: they more often gave answers in accordance with normative ones, demonstrated a categorical level of generalizations. It should be noted that when performing the task in simple cards, patients with schizophrenia also demonstrated oculomotor activity trends similar to the normative group: they fixed their gaze on the correct answer (image) for a longer time and more often.

In the regulatory group as a whole, there were fewer fixations on all 4 images in the cards. When performing the task of identifying a significant feature in simple cards, healthy respondents revealed 2 patterns of eye movement: 1) in some cases, healthy subjects made long–term fixations on 2-3 images, excluding the "extra" object (correct answer); generalization was made at the categorical level; 2) in other cases, the subjects examined all 4 images in the card, but noted a longer fixation on the "extra" object (correct answer) and also Generalization was made at the categorical level. Thus, oculomotor characteristics in the normative group differed in the minimum number of fixations, shorter duration of fixations, absence of long-term fixations on all images, absence of fixation, or an increase in fixation time on an "extra" object (Figure 1). Normally, the images in the cards were studied mainly sequentially, the algorithm "in a circle" (or square) was used more often or the diagonal type (Figure 2).

Figure 1 Movement of the gaze in the normative group when solving the problem of identifying an essential feature at the categorical level of generalization in the "Exclusion of the fourth superfluous" method

 Figure 2. The movement of the gaze (circular or diagonal types of examination of objects) in the normative group when solving the problem of identifying an essential feature at the categorical level in the "Exclusion of the fourth superfluous" method

Patients with schizophrenia demonstrated a greater number of fixations, a more detailed study of the details of the drawings, followed by a return to them, fixation outside the studied pictures. There were also different types of algorithms for gaze movement when studying images: linear, diagonal, circular. When examining images in cards of a simple level of complexity, patients with schizophrenia showed similar trends to the normative group: a small number of fixations, decision-making is carried out based on the consideration of 2-3 items on the card with an effective solution to the problem. However, in some of the cards, patients with schizophrenia demonstrated cases of chaotic gaze movement, which may indicate difficulties in finding and highlighting a common feature in the depicted objects (Figure 3, Figure 4, Figure 5).

Figure 3 Gaze movement in a group of patients with schizophrenia with fixation outside the study area when solving the problem of identifying an essential feature at the categorical level of generalization in the "Exclusion of the fourth superfluous" technique

Figure 4 Gaze movement in a group of schizophrenia patients with multiple fixations on details when solving the task of identifying an essential feature at the categorical level of generalization in the "Exclusion of the fourth superfluous" method

Figure 5 Gaze movement in a group of schizophrenia patients with a small number of fixations when solving the task of identifying an essential feature at the categorical level of generalization in the "Exclusion of the fourth superfluous" method

Next, oculomotor characteristics were analyzed normally and in patients with schizophrenia when considering cards of a more complex level and highlighting the "superfluous" object. The answers were also compared at the categorical, specific-situational level of generalization and on the basis of latent features. The following trends were found.

In the normative group, when solving complex problems, longer fixations and a higher frequency of gaze fixations were carried out on the stimulus image, which was "superfluous" in the card, and these were the correct answers.

In the subgroup of schizophrenia patients who gave correct answers at the categorical level of generalization, patients also showed trends similar to the normative group.

In the subgroup of schizophrenia patients who gave incorrect answers based on the actualization of latent signs, patients did not fix their gaze on the correct "superfluous" objects, but looked at all four images for a longer time. I.e., in the decision-making process, the gaze stopped longer not on images that are "superfluous", from the point of view of most healthy people people, and in completely different images-stimuli. For example, in the card "drill, screw, saw, axe", patients with schizophrenia of this subgroup viewed the image of a saw more often and for a longer time; in the card "guitar, radio, phone, envelope" - they looked at all 4 pictures for the same time; in the card "umbrella, cap, pistol, drum" - they fixed their gaze on the pistol for a longer time. And as a result, these patients solved the problem of choosing an extra item in the card completely randomly, more often based on the actualization of a latent feature and gave the wrong answer.

When evaluating the movement of the gaze in the process of examining the cards and choosing an "extra" object, we found the following pattern: in the normative group, the first fixations on the stimulus are aimed at recognizing the object (2-3 fixations), the study of objects on the card was carried out mainly using two algorithms – in a circle (clockwise or counterclockwise) or diagonally. The minimum number of fixations (2-3) is sufficient for the image to be perceived holistically, and essential features for generalizing objects were highlighted (Figure 6). After the process of searching for an answer to the task begins, more gaze movements on objects are required to compare them and select a grouping feature: which object is superfluous from the 4 presented in the card. Healthy respondents were more likely to generalize based on the minimum number of fixations.

Figure 6. The movement of the gaze in the normative group when solving a problem (cards of a complex level) to identify an essential feature at the categorical level of generalization of the "Exclusion of the fourth superfluous" technique

Patients with schizophrenia found a greater number of fixations and gaze movements, as well as slipping from the field of images (Figure 7) when examining objects in complex cards; there was a sequential or alternating comparison, separate parts of the image (details) were considered, chaotic viewing was often observed (Figure 8, 9, 10).

Figure 7 Movement of gaze and sliding from the image field in a group of patients with schizophrenia when solving a problem in the cards of a complex level of the "Exclusion of the fourth superfluous" technique

Figure 8 Gaze movement and fixation on individual image details in a group of patients with schizophrenia when solving a problem in the cards of a complex level of the "Exclusion of the fourth superfluous" technique

Figure 9 Gaze movement and chaotic viewing in a group of patients with schizophrenia when solving the problem of identifying an essential feature in the cards of a complex level of the "Exclusion of the fourth superfluous" technique

Figure 10 Gaze movement in a group of patients with schizophrenia when solving a problem based on the actualization of a latent feature in the cards of a complex level of the "Exclusion of the fourth superfluous" technique

Therefore, based on the objective registration of eye movement, we can conclude that a longer fixation of the gaze on the object (image) and a smaller number of fixations on the remaining images of the card may normally indicate the process of choosing a grouping feature. Chaotic eye movements, a large number of fixations in the absence of fixation on any one (superfluous) object reflect the difficulties in finding common links between the depicted objects and choosing a significant grouping feature.

Conclusion

Thus, during the experiment, in which eye movements were recorded with the help of an eye tracker when solving a mental task to search for a common essential feature in images of objects with the allocation of an unnecessary (unsuitable) object in the "Exclusion of the 4th superfluous" method, patterns characteristic of both healthy respondents and patients with schizophrenia were obtained: characteristics eye movements reflect an active process of cognitive processing of information or its difficulties. Thus, prolonged fixation of the gaze on an object (image) against the background of a decrease in the number of fixations on other images may indicate the process of cognitive analysis and choice and decision-making on this basis. Chaotic eye movements, a large number of fixations in the absence of fixation on any one object reflect the difficulties in finding meaningful information for decision-making.

Statistically significant differences in oculomotor (oculomotor) activity in solving mental tasks were also obtained between a group of healthy subjects and a group of patients with schizophrenia:

The normative group produces a minimum number of visual fixations when considering stimulus images in the cards: the first fixations are aimed at recognizing and holistic perception of the object (2-3 fixations); subsequent fixations demonstrate the process of comparing/comparing objects and highlighting an essential, grouping feature for their generalization. At the same time, healthy respondents mainly use two types of algorithms for gaze movement in the process of solving a given mental task: in a circle (clockwise or counterclockwise) and diagonally.

A small number of fixations in the regulatory group may be associated with faster fixations of less than 70 ms, which go beyond the sensitivity of the device.  Despite the fact that longer gaze stops (from 100 ms and above) are considered to be fixations (Wass, S.V., Smith, T.J. et al, 2013), a number of researchers believe that the minimum fixation time should be 50 ms (Barabanshchikov V. A., Zhegallo A.V., 2014).

When solving the generalization problem in the "Exclusion of the fourth superfluous" method in patients with schizophrenia, in comparison with the normative group, an increase in the frequency of visual fixations, the duration of fixations, and an increase in pupil diameter are noted at a high level of statistical significance. In addition, there were slips from the image field when viewing images, a large number of fixations on individual parts of the image (details), chaotic viewing, which may indicate difficulties not so much in the holistic perception of images as in mental operations of comparing and generalizing the depicted objects based on a common grouping feature. As a result, patients with schizophrenia were more likely to give incorrect answers based on random, insignificant, latent signs that did not reflect the real relationships between the objects depicted in the cards. When generalized by latent feature, patients with schizophrenia showed fewer visual fixations on obvious, "correct" superfluous objects and a longer fixation time on all other images, which may indicate a violation of selectivity in the process of visual perception and violations of selectivity and criticality in the process of mental activity. It can be assumed that in the process of comparing the visual stimuli presented on the cards of the "Exclusion of the 4th superfluous" technique, it was difficult for patients with schizophrenia to identify and select the most significant (essential) signs and properties of the depicted objects from the entire volume of diverse visual information. As a result, it was difficult for them to identify a common grouping feature and identify an "unnecessary", unsuitable object.

If we draw an analogy of the observed phenomena with phenomena from Gestalt psychology, then it can be assumed that patients with schizophrenia have difficulty distinguishing a figure from the background, but not at the level of visual perception, but at the level of basic thought processes, where it is necessary to highlight the main feature of an object or phenomenon against a wide range of concomitant various signs.  

At the same time, it should be noted that when solving simple cards, patients with schizophrenia demonstrated a sufficient level of productivity in identifying essential features and trends similar to the normative group, using mainly linear, diagonal, circular types of eye movement algorithms when viewing images. The only thing that distinguished them from healthy respondents was the total number and duration of visual fixations when viewing images in the cards. Patients with schizophrenia spent significantly more time studying the visual stimulus and committed a greater number of fixations when choosing a grouping feature for generalization.

When solving complex cards, patients with schizophrenia who gave correct answers at the categorical level of generalization showed trends in eye movements similar to the normative group. When solving complex cards with the allocation of an incorrect "superfluous" object (based on latent signs), patients with schizophrenia either looked at all 4 images in the card for a long time, getting stuck on the details without fixing their gaze on one thing, which reflected difficulties in identifying a significant, common feature or property of the object, or considered incorrect "superfluous ones for a longer time" objects.

Thus, the conducted research allowed us to conclude that eye movements in solving cognitive tasks to determine a significant common feature in the images of objects presented on the cards accompany the cognitive information processing process and reflect its 2 stages: 1) the recognition of visual images presented on the card is a stage of visual perception; 2) the nomination and verification of hypotheses, analysis, comparison and generalization of visual stimuli, the formulation of an answer (inference) is actually a thought process.

The patterns of oculomotor activity in solving cognitive tasks in healthy subjects and in patients with schizophrenia have been determined. The use of an eyetracker in the study allowed an attempt to objectify the assessment of violations of the process of searching and highlighting a significant (essential) feature of objects through the registration of eye movements when solving the problem of generalizing objects and excluding the 4th superfluous. It has been established that chaotic eye movements reflect impaired mental activity and are associated with the main problem of cognitive activity in patients with schizophrenia - with the choice of a significant (main, essential) feature or property from the whole variety of perceived stimuli.

Limitations and prospects of the study: this study, conducted using the method of contactless registration of oculomotor activity using an eyetracker, leaves the question unresolved at what stage of information processing (thought processes) a failure occurs in solving cognitive tasks in patients with schizophrenia. The problem of objective diagnosis and assessment of mental disorders remains unresolved, and the use of this method alone does not provide a complete picture of these disorders.

In our opinion, a promising step in the study of cognitive disorders in schizophrenia may be the organization and conduct of an experiment that will allow us to consider objectively and in more detail the psychophysiological and neuropsychological levels and stages of the process of solving logical problems and the mechanisms of its violations.