A 14-year-old girl complains of indistinct pronunciation that showed up at the age of 14 after the acute respiratory viral disease. Examination revealed normal face and normal teeth alignment, occlusal disharmony was not found. Palpation did not reveal cleft palate. Uvula does not move during pronunciation of sounds, its palpation does not cause gag reflex. What is the cause of indistinct pronunciation of sounds?