A double organ transplant recipient, Elizabeth has developmental delays and speech problems because of a birth defect.
From the chron.com
When listening in the presence of background noise, the damaged high-frequency portion of your hearing organ cannot provide you with accurate high-frequency speech information.
From the nytimes.com
Inside the organ of Corti are the ultra-sensitive hair cells, whose movement in response to vibrations creates the nerve signals that are fed to the brain and interpreted as sounds and speech.