Hearing loss in one ear is often described as unilateral hearing loss, or single-sided deafness (SSD). SSD is a type of hearing loss where there is a complete hearing loss in one ear and anything from normal hearing to profound hearing loss in the other ear.
These difficulties are the result of a phenomenon called “the head shadow effect”. The head shadow effect describes the effect of high-frequency sounds which cannot be perceived due to their inability to travel around the head to reach the functioning ear. The high-frequency sounds, including many sounds used in speech, are “shadowed” by the head and are lost to the person with SSD. Low-frequency sounds, however, can bend around the head to reach the functioning ear. This makes sound depth perception difficult for the brain and sounds may seem flat or muddled, like when we try to speak to someone in a noisy environment and their voice becomes lost, or when someone at the other end of the phone is in a crowded street.