Summary: we’re not sure.
After a post we featured earlier this year on whether deaf people can hear hallucinated voices, I was sent an amazing study that attempted to distil the variety of ‘hearing voices’ experiences in deaf people.
It was published in the journal Cognitive Neuropsychiatry in 2007 (there’s a full text copy available online as a pdf) and attempted to avoid some of the pitfalls of studying auditory hallucinations in people with absent or limited hearing.
Some of the earlier research on deaf people who hear voices has been criticised for assuming that when a deaf person describes a ‘voice’ it automatically means they are having a similar experience to hearing people.
For example, when a deaf person describes the experience as ‘loud’ they may just mean it is particularly intrusive, rather than that it has specific auditory properties.
This later study used a sorting method, were a number of statements about what the experience could be like (some illustrated) were presented to deaf participants and they are asked to select the ones that best describe their experiences.
See also: Do blind people hallucinate on LSD?