Hearing plays a key role not only in the perception of information from the environment and the formation of speech, but also in social construction, communication and the maintenance of important cognitive functions. At the same time, persistent hearing loss can lead to cognitive disorders and dementia, as well as central auditory dysfunction. Subjective methods of hearing research were used — pure tone threshold audiometry (PTA), speech audiometry in silence and noise; and objective diagnostics — recording of long-latency auditory evoked potentials (LLAEP). Hearing aid rehabilitation of patients with bilateral hearing loss leads not only improve the quality of life, but also helps to prevent disorders of memory and attention. Clinical examples show the difference in speech intelligibility between patients with permanent hearing loss rehabilitated with one and two hearing aids, as measured by speech audiometry. In addition, it is investigated whether the side of the prosthesis affects the state of the cortical centers of the auditory analyzer as measured by long-latency auditory evoked potentials (LLAEPs).