[The Spatial-Frequency Characteristics of the Visual System in Schizophrenia].

In order to determine the spatial-frequancy characteristics of the visual system of healthy subjects and patients with schizophrenia, we used the contrast comparison of two Gabor gratings with sinusoidal distribution of brightness. The Gabor gratings have low, medium or high spatial frequencies; the neurons of magnocellular and parvocellular channels are sensitive to these frequencies to different extents. We found an increase in sensitivity to the contrast when comparing the gratings with low frequencies (to which magnocellular channels are most sensitive) in the patients with first-episode schizophrenia who had not receive long-term antipsychotic treatment, as compared with the control group. On the contrary, the sensitivity to the gratings with medium and high spatial frequencies in this group of patients was lower, as well as in patients with first-episode schizophrenia who had received long-term treatment. The patients with chronic schizophrenia showed a decrease in contrast sensitivity in all tested ranges of frequencies. We obtained supplementary evidence of the enhancement of internal noise in the visual system of the patients with schizophrenia. The results help us to explain the clinical data on the development of visual perceptual diorders at different stages of schizophrenia.

[The frequency-contrast sensitivity of visual stimulus perception in patients with schizophrenia with the therapy of atypical and typical antipsychotic drugs].

We studied the effect of typical and atypical antipsychotics drag treatment on the perception of visual stimulus which activates preferentially different visual channels. We recorded contrast sensitivity in normal and schizophrenic patients. Elements presented with Gabor-like gratings with sinusoidal distribution of brightness, spatial frequency: 0.4 cycles/degree, 3.6 and 17.9 cycles/degree. Patients were divided into two groups. One group--patients treated with atypical antipsychotics, and the second group--patients treated with typical antipsychotics drags. Registered a decline compared with the normal contrast sensitivity for low and medium spatial frequencies. We observed significant difference between two groups of patients in the range of low spatial frequencies.

[The efficiency of recognition of the size of segments of line by the observers with different parameters of the cognitive style].

We estimated efficiency of recognition of the size of segments of line by the persons with different parameters of cognitive style: the field dependence--field independence, the analytically--synthetically style, the flexible--rigid cognitive control. The size of segments of line was judged in task of the magnitude of the Ponzo illusion measurements. It was established, that the magnitude of the Ponzo illusion significantly less in subjects with the field independence cognitive style, than with field independence. The persons with the flexible type of the cognitive control showed the tendency to more accurate perception of the size of the segments in the Ponzo figure, than with the rigid cognitive control. The rinteraction between the analytically--synthetically style of the categorization and the magnitude of the Ponzo illusion is not fixed.

[Evoked potentials and processing of visually presented Poggendorff figure].

We have been studying association between distorted perception and visual event-related potentials, which appear in response to the Poggendorff figure's presentation in Jastrow modification. It was shown that the amplitude sign is determined by the presence or absence of subjective distortion at the earliest and the latest phase of Poggendorff figure's perception. The amplitude of the wave P150 was bigger at the distorted perception, and the amplitude of the waves N200 and P300 was smaller than during perception without distortion. It is suggested that both ascending nervous processes and cognitive processes of analysis are involved into the emergence of the Poggendorff illusion.

[Features of perception of length of segments under conditions of ponzo and Müller-Lyer illusions in schizophrenia].

In order to better appreciate the neurophysiologic mechanisms of perception of length under conditions of geometrical visual illusions, we studied sensitivity of mentally healthy subjects and schizophrenic patients to Ponzo and Müller-Lyer illusion. Patients with schizophrenia estimated length of segments of Müller-Lyer figure less precisely. Accuracy of perception of length of segments in Ponzo figure was ambiguously connected with the duration of the disease. Persons suffering from schizophrenia for a short time were less inclined to Ponzo illusion than mentally healthy subjects. On the contrary, patients who suffered from schizophrenia for a long time were more sensitive to this illusion. Ponzo illusion can be used as a marker of schizophrenia which is found out during the specific period of development of the disease. High sensitivity of patients with schizophrenia to Müller-Lyer and Ponzo illusions supports a hypothesis about the role of the global analysis of an image during processing of its low-frequency component in formation of the illusions under study.

[The contrast sensitivity in schizophrenia with different durations disease].

We recorded contrast sensitivity in normal and schizophrenic patients. We presented Gabor gratings with sinusoidal distribution of brightness, with the spatial frequency: 0.4 cycles/degree, 3.6 and 17.9 cycles/degree. Taken together patients with schizophrenia compared to the healthy subjects showed a decline of contrast sensitivity at low and medium spatial frequencies. We measured the influence of duration of illness and type of treatment on contrast sensitivity. Patients with schizophrenia less than 10 years, showed a decrease of contrast sensitivity only at low spatial frequencies, while patients suffered with schizophrenia for more than 10 years--at low, medium and high spatial frequencies. Persons with schizophrenia less than 10 years receiving treatment with atypical antipsychotics, show a decrease in contrast sensitivity at low spatial frequencies, while treated with typical antipsychotics--in the low and high spatial frequencies.

[Study of parvocellular and magnocellular visual channels in normal subjects and in patients with psychopathology].

We measured susceptibility to the Müller-Lyer illusion in schizophrenic patients and normal observers. The images of the Müller-Lyer figure were digitally filtered in a high-frequency and low-frequency band by wavelet filter. Patients with schizophrenia are more susceptible to Müller-Lyer illusion, than mentally healthy examinees. The images of the Müller-Lyer figure with low spatial frequency were perceived in a similar way by the schizophrenic patients on the initial stage of disease and the control subjects. Patients with schizophrenia were more sensitive to the Müller-Lyer illusion when the image contained only high or medium spatial frequency. Schizophrenic patients in advanced stage were more susceptible to the illusion while presented with all types of images of the Müller-Lyer figure than the control group. It is hypothesized that those differences arise from the mismatch work of the magnocellular and parvocellular systems. It is known that images with the high spatial frequencies are most relevant for the parvocellular visual channels. The magnocellular visual channels are most sensitive to the images with the low spatial frequencies. Thus these findings demonstrate a significant impairment in parvocellular pathway function in patients on initial stage of schizophrenia. The patients on advanced stage of schizophrenia demonstrate impairment of both the parvocellular and magnocellular systems.