vflyer This is a simple explanation while not physiologically perfect will convey the concepts:
Recruitment is defined as an unnatural increase in loudness of sounds resulting in louder sounds causing discomfort and distortion. It usually accompanies moderate to profound loss. A normal hearing person can hear quite loud sounds with comfort and no distortion because the mammalian human ear attenuates the sound before it gets to the sensitive inner hair cells.
The inner ear system (cochlea) uses a two step method to handle sounds. The sounds enters the cochlea and must pass through a line of outer hairs to get to the inner hair cells. The outer hairs attenuate loud sounds and actually boost soft sounds. (they do other stuff too like modulate the sounds)
The resultant sound waves then go to the inner hair cells which line the entire length of the cochlea. Each clump of inner hair cells is tuned to a different tone (frequency). If any of these clumps of inner hair cells dies or degenerates that tone will not be heard as the correct tone. It may induce nearby healthy clumps of inner ear hair cells to register a signal to the brain (auditory cortex) at their own specific natural tuned tone…but not at the correct tone.
What that means is, if you have dead inner hair cells. some sounds simply will not be heard or if heard will not be the right tone. This of course means that speech comprehension will be reduced.
Technical Note: This is why the typical pure tone audiogram is not 100% reliable for those with high recruitment and/or dead regions. Masking the other ear won’t help. Prof. Dr. CJ Moore, Cambridge University, says the only way to clearly identify the dead frequencies is to mask around the inserted frequency. or TEN test) Ed