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.

The data was then analysed using factor analysis – a statistical procedure that, in this case, was used to group participants whose experiences were similar.

Five groups or ‘factors’ were found, and I’ve reproduced the descriptions below as they are a completely fascinating insight into how these experiences appear in their diverse and varied forms.

Factor A: Nonauditory voices with subvisual perception of voice-articulators in the mind‚Äôs eye These experiences were mostly reported by profoundly deaf participants who were deaf at birth or before the development of language. Voices were reported to be nonauditory, clear, and easy to understand. Participants were certain that they did not hear any sound when voices were present. They did not consider questions about pitch, volume, and loudness relevant to their experiences. Participants knew the identity and gender of the voice but did not deduce this information from the way it sounds. They reported seeing an image of the voice communicating with them in their mind‚Äôs eye when voice hallucinations were present. All participants had experienced seeing an image of the voice signing or lips moving in their mind. Imagery of fingerspelling was also seen but was less common. These images appeared to be subvisual in nature and distinct from true visual hallucinations. They were clearly understood as originating internally and several participants stated that the image could still be perceived with their eyes closed. Factor B: Mixed perception and uncertainty about how voices are perceived. These experiences were mainly reported by deaf people who had experience of hearing speech and used hearing aids. The participants were uncertain about whether their voice hallucinations were auditory in nature. Comprehensibility and clarity are variable. The voice used speech/lip movements to convey its‚Äô message and occasionally fingerspelling and gesture. The voice was perceived as sometimes being silently articulated and sometimes having sound. Participants were uncertain if the voice was mouthing with or without vocalisation. Despite this uncertainty, Participant 10 was able to make attributions about voice pitch, volume, and loudness. No primary visual hallucinations were reported, although Participant 10 described seeing a stationary image of her deceased husband when the voice was present. There was less certainty about whether a visual image was present when the hallucinations occurred but participants agreed that the hands/lips of the voice could be perceived but that they were unclear. Strange sensations were perceived in the body both when the voice was present and not present. These included the perception of air currents, electric currents, and vibrations. Factor C: Poorly defined voices. These experiences were largely reported by participants who were born deaf in developing countries and spent their early years without hearing aids or formal language, only acquiring sign language as their first language after moving to the UK after the critical period for language development The voices were poorly defined, hard to understand and unclear, with no definitive statements about exact voice properties but rather a picture of what they were not. There were contradictory responses about whether the voices made sound or not. It was not clear whether participants were completely unable to make judgements about pitch and volume because the voices were not auditory in nature, or because they did not possess a sufficiently developed concept of sound-based descriptions. There was a great deal of uncertainty about voice genesis that may have led the participants to speculate that they might be ‚Äò‚Äòhearing‚Äô‚Äô something when they were present. This factor is unique because participants did not perceive imagery of the voice articulators during hallucinations. The gender and identity of the voice were unknown and there was much more uncertainty about which language or modality the voice used to communicate. Participants were unable to articulate voice content but merely described a sense of being persecuted and criticised by an external other. Factor D: Auditory voices. These experiences were reported by deaf people who were born moderately or moderately severely deaf and used hearing aids. Voices were auditory and participants report that they could always hear sounds when the voices were present. Participant 11 was able to make judgements about auditory properties including pitch and volume. Participant 7 was less able to provide qualitative description of acoustic aspects but she was convinced that she could hear the voices. Interestingly, the bilingual participant showed a mixed pattern of voice perception. She experienced predominantly auditory hallucinations but also reported silently articulated sign language hallucinations, with concurrent subvisual imagery of the articulators similar to those experienced by participants on Factor A. Factor E: Voices and true visual, olfactory, gustatory, and tactile phenomena These experiences were reported by two deaf participants who were both profoundly deaf. This factor was distinguished by the presence of true visual, auditory, olfactory, and gustatory phenomena, which occurred separately to voice hallucinations. These included tinnitus, the perception of a black shadow darting through peripheral vision, strange smells emanating from the body, and a petrol taste in the mouth. Other phenomena occurred in conjunction with the voices such as vibrations and electric currents in the body, which occurred only when the voice was present. Participant 25 reported seeing a true visual hallucination of someone signing to her in real space as well as imagery of the voice in her mind‚Äôs eye.

Thanks to Mind Hacks reader Sanjay for sending me the study.

Link to PubMed entry for Cognitive Neuropsychiatry study.

pdf of full text of study.