Chronic alcoholism could contribute to impairment of nerve system and brain functions, even some psychiatric disorder such as hallucination, heteroptics, acousma and so on.
After a particularly difficult period living with Paul Gauguin, he suffered an attack of acute mania, culminating in hallucinations and hearing voices, which led to him cutting off his own ear.
Clinical studies done at Stanford University show that people who have auditory hallucinations, such as schizophrenia, have voices that are shaped by cultural influences.
In one published in 2017, for example, participants with schizophrenia who had experienced auditory hallucinations tended to have thinner auditory cortexes than those who hadn't.