Do deaf people hear hallucinated voices?

I always assumed the question of whether people deaf from birth could hear hallucinated voices was similar to the question of whether a tree falling in a forest makes a sound if no-one is there, but it turns out that there have been several studies on auditory hallucinations in deaf people.

In fact, I’ve just read a remarkable paper that reports ten case studies of people who became deaf before they learnt language and who report hearing voices as part of a psychotic mental illness. And this isn’t the only study, PubMed has several more.

I always assumed that a born-deaf person would hallucinate signs instead (and apparently, this has also been reported) but this study carefully asked the people concerned about and they seemed to be clear that they were ‘hearing’ the voices.

In one of the most interesting bits in the study they asked the deaf patients how they could ‘hear’ voices when they were deaf:

Although the patients were only rated as having auditory hallucinations if they were emphatic that they heard voices rather than received information in some other way, and several gave the sign for talking, questioning about how they were able to hear, being deaf, was typically uninformative. Most commonly the patients merely shrugged, gave a ‘don’t know’ reply, or indicated that they could not understand the question.

Others made attempts at explanation which were superficial, facile or otherwise unsatisfactory, such as ‘maybe talking in my brain,’ or ‘sometimes I’m deaf, sometimes I hear’. One patient argued that he could hear music if he turned it up loud (which probably represented perception of vibration), and implied that the same was true for speech. Still others made untrue or delusional claims that they could hear or used to be able to hear.

Such patients made statements like ‘I’m not deaf‘, or ‘I can hear on one side, on the right’, or ‘I used to be able to hear a little, a year ago’. One patient, who was diagnosed as deaf at the age of 2 years, stated that she could hear before the age of 5 years, but then she hit a brick wall and became deaf. One patient believed that his hearing had been restored by God.

These sorts of seemingly half-hearted explanations are not uncommon in patients with delusional syndromes. For example, if you ask a patient who is paralysed after brain damage but is unaware of it (something called anosognosia) to lift their hand they can often give answers like “it’s fine where it is” or “I can’t be bothered right now” while continuing to claim that they could move it if they wanted.

I notice a recent article criticises the idea that deaf people can hear voices saying that the interpretation of these hallucinatory experiences relies on hearing people imposing their ideas onto what they’ve been told. In the case studies above some of the deaf people clearing and unambiguously signed that they ‘heard’ the voices but sadly I don’t have access to this critical article so can’t say quite how convincing this argument is.

On a related note, I’ve heard several people discuss whether blind people could experience ‘visual’ hallucinations (usually in reference to LSD) but I’ve had no luck finding any reports of this.

Link to study of hallucinated voices in deaf people.
Link to PubMed entry for same.