A patient with sensorineural hearing loss can have the symptom of hearing double in the damaged ear. Not having a time-delayed echo, but hearing as if he (or other people) speak with two voices at once. Is there a theory about the mechanism behind this? Does it happen on the level of the malfunctioning hair cells, or because the brain has trouble remapping an incomplete input of frequencies, or something else? 
What is the neurophysiological mechanism behind double hearing?
neurobiology;perception;cognitive neuroscience