IAI does not only play a functional role but also has qualitative and quantitative characteristics. Biological significance of IAI consists in mobilization of some sensory functions and demobilization of others as a response to a stimulus signaling changes in the environment. This constitutes one of the manifestations of body's preparatory reactions for action in the forthcoming situation. It has been established that in patients with psychic pathology such preparation of the body systems is affected, which may manifest through changes in illusion frequency.

To apply Charpentier illusion to research IAI characteristics with the purpose of further detection of abnormalities in the sphere of intermodal interaction.

One of the IAI research methods, is illusion research, e.g. Charpentier illusion, since it is based on interaction between visual and proprioceptive analyzers. Changes in preparatory reaction in subjects with psychic pathology is characterized by decline in illusion frequency, patients in these conditions should evaluate stimuli more correctly than healthy participants. Pre-experimental research design included two subjects: with white matter pathology (patient G., male, 27, full agenesis of CC, based on MRI results) and with IDD (subject A., male, 30).

Research subjects demonstrated absence of illusions, which is indicative of functional weakness of IAI, which results in inconsistency of sensory systems and meaningless perception. IAI plays an important role in formation of human psyche by enabling the development of significant patterns underlying human cognitive activity.

Illusion research is relevant for clinical psychological diagnosis of diseases associated with integrative brain activity disorders.

The authors have not supplied their declaration of competing interest.