Abstract: The objectification of diagnostics is one of the urgent problems of psychiatry. The aim is to study the relationship between changes in contrast sensitivity and cognitive impairment in schizophrenia and depression. The contrast sensitivity parameters were considered to be evidence of the functional state and the nature of interaction of the magnocellular and parvocellular visual systems, which provide mechanisms for global and local information analysis. The relationship between the features of their interaction with the processes of memory, attention, and thinking in schizophrenia and depression has been established. In schizophrenia, there is a mismatch in the functioning of the magnocellular and parvocellular neuronal systems, with a decrease in the activity of both systems. In depression, the level of activity of the magnocellular system is preserved, while the activity of the parvocellular system is significantly reduced. Thus, in depression, a different mismatch in the interaction of the magnocellular and parvocellular systems is observed compared to schizophrenia. The relationship of the activity of the magnocellular system with the characteristics of working memory and the properties of attention is shown. The balance shift towards the activity of the magnocellular system is accompanied by impaired selective attention and decreased voluntary regulation. Regarding thinking, the interrelation of the magnocellular system with the processes of abstraction and categorization and that of the parvocellular system with the selection and assessment of significant features is shown.