DEVELOPMENT OF BABY HEARING
The fetus in the womb hears sound that is transmitted by liquid, which softens or muffles the sounds to some extent. After birth, babies hear a variety of sounds, yet tend to be disturbed only by the sudden loud noises. These “violent” sounds elicit the startle reflex, seen as a jerking of the head backward, bulging of the eyes, and flexion of the elbows.
ANATOMY OF BABY’S EAR
There are two distinct branches of the auditory nerve. One is the cochlear branch which carries sound information to the brain and the other is the vestibular branch which detects motion and tells us where we are in space. Anatomy books show how closely these two branches are interconnected. We also know that the stimulation of a nerve in a baby travels through the body more than in an adult. For example, if you scratch a baby’s foot, the muscles of the entire body respond. When a baby hears a loud sound, since these two branches are close together and newly developing, the strong stimulus travels over to the vestibular branch of the same nerve. Thus, the baby not only hears the sound (cochlear branch) but physically feels it in his limbs (vestibular branch). His head jerks backward, deepening the physical sensation when the movement of the fluid in the ear further stimulates the vestibular branch. It is possibly experienced as pain, suggests Dr. Moshe Feldenkrais in his book The Elusive Obvious, which examines fundamental physiology patterns in humans.
The above video from oleviasea’s youtube channel is one clear example of this reaction. In this situation, the father’s snoring is staged, but the baby’s reaction is not. The noise is indeed near the threshold of feeling.