Now there’s growing evidence that the causes of problems processing speech amid noise are different than the causes of problems hearing sound. Scientists believe exposure to loud noises can erode the brain’s ability to listen selectively and decode words, without causing traditional hearing damage. Difficulty understanding speech amid noise can set in long before traditional hearing loss.
Hearing loss in adults is usually associated with damage to the tiny hair cells that line the inner ear and transfer sound signals to nerve fibers that lead to the brain. Aging, trauma and noise exposure can all cause those hair cells to deteriorate.
New research suggests that the synapses connecting the hair cells to nerve fibers are even more vulnerable and suffer permanent damage long before the hair cells deteriorate, bringing about the difficulties in selective listening.