Robin Paijmans, Clinical Psychologist, Denmark House, Birmingham
Jim Cromwell, Clinical Psychologist, National Deaf Services, London
Sally Austen, Consultant Clinical Psychologist, Denmark House, Birmingham
Abstract
The psychiatric literature has described profoundly prelingually deaf people with psychosis reporting hearing voices. We propose that such reports reflect the beliefs of professionals in mental health and deafness and not a hallucinatory experience of psychotic deaf people.
We demonstrate that it is functionally meaningless to assert that a prelingually profoundly deaf psychotic patient “hears voices”, and provide a theoretical structure from which to more appropriately consider the internal experiences of deaf psychotics, and to encourage the clinically relevant articulation of them. We also suggest that the “true” phenomenological experience is of secondary clinical interest to the meaning imposed upon it by the client and the distress caused by it.
Introduction.
The psychiatric literature has frequently made mention of the counter-intuitive finding that profoundly prelingually deaf people with psychosis report hearing voices. For instance Critchley et al. (1981) studied twelve apparently prelingually profoundly deaf psychotic patients and reported that ten patients reported visual hallucinations, and that ten patients also described experiences “analogous to auditory hallucinations” although the authors concluded that “voices may not have been heard”. Schonauer et al. (1998) interviewed 67 prelingually deaf schizophrenic patients, in sign language, about their hallucinatory experiences over the entire course of their illness and also reviewed clinical records of their previous admissions. Deaf psychotic patients reported much more visual and tactile hallucinations compared to hearing psychotic patients. Although some deaf patients reported visual hallucinations of sign language messages, the hallucinatory reception of meaningful information appeared associated with the 'auditory' modality. The authors considered that deaf patients might be imagining in their own way what “hearing” might be, even though they had never experienced it. Du Feu and McKenna (1999) translated the structured Present State Examination psychiatric interview into sign language and interviewed 17 schizophrenic and schizoaffective patients, with onset of profound deafness prior to the age of 2 years (as far as could be ascertained), and attempted to evaluate whether these patients might in reality be describing other symptoms. Ten patients gave accounts of verbal auditory hallucinations with description of content and spatial localisation (although not voice quality). These did not appear to be attributable to other psychotic experiences and showed typical characteristics of schizophrenic hallucinations. The symptom was present in six patients who had been deaf from birth or early infancy. Interestingly when asked how they could hear voices if they were deaf, patients typically were unable to give an explanation, or would (incorrectly) claim that they had acquired hearing. One patient believed that his hearing had been restored by God. The authors concluded that auditory hallucinations may be a common phenomenon in profoundly prelingually deaf psychotic patients.
Although some phenomenological analysis has been attempted of these experiences, so far no clear explanation has been offered to account for them. How can profoundly prelingually deaf people, who have never heard a voice, know when they experience the hallucination of one?
Issues of methodology.
Degree of deafness:
As the above authors have noted, research into this topic is fraught with methodological problems. The first difficulty is to obtain a sample of research participants who are truly profoundly prelingually deaf. Deafness is not a uniform phenomenon but exists to varying degrees, ranging from profound prelingual deafness, in which the person has had no experience of hearing sound at all, to restricted hearing only in those frequencies required for verbal communication, to central auditory processing deficits in which a person has the full frequency range of hearing but cannot meaningfully process these sounds. Without thorough audiological testing it is not always clear what the actual residual hearing capability of a deaf psychotic patient is. Therefore whether this patient does have some experience of hearing to form the basis for experiencing or making sense of auditory hallucinations, remains unclear.
Onset of deafness:
Similarly even with early onset profound deafness it is often difficult to establish at which point exactly a person became deaf. Traditionally, a baby is seven to eight months old before the health visitor carries out a ‘distraction test’: the baby sits on her parent’s lap and is encouraged to play with a toy, while the health visitor makes sounds out of sight to both the left and right of the child to see whether they will notice and turn to localise the sound. This distraction method fails to detect three quarters of the children born deaf each year in the UK, which means that many children with hearing problems are not identified until they start school. However conversely, unless a clear congenital cause can be identified in hindsight, it is impossible to say for certain whether a child was profoundly deaf before it started school or whether progressive hearing loss only reached that stage just prior to the time of diagnosis. With modern advances in technology, more recently babies can be given the minute-long Oto-Acoustic Emission test, within two days of birth. The test involves sending sound into the baby’s ear and measuring the level of sound returned, enabling hearing function to be calculated. A similar test is the Auditory Brainstem Response test, which registers neurological responses to auditory stimulation. Furthermore reliable genetic screening of congenital deafness through a simple blood test is now becoming available (Preciado et al. 2004). Nowadays, therefore, the onset of deafness can be much more reliably determined. However with older generations, time of diagnosis may have been as late as four to five years of age, at which point their previous hearing experience may remain shrouded in mystery.
This is critical because the first four to five years of a child’s life appear to be the most vital in terms of acquiring spoken language. At the age of six to eight months the infant is already acquiring the first fundamentals of its native language, its brain dynamically “tuning” the cochlear to be sensitive to the phonemes and frequencies relevant to that language (in illustration the Chinese and Japanese language does not discriminate between “L” and “R” sounds, and typically native Chinese and Japanese speakers cannot distinguish between these sounds either). As such the decoding of speech is an active central auditory process based on prior exposure and learning of what are meaningful sounds during the early life stages critical to language development (e.g. Kuhl et al. 1992). This means that a person’s hearing experience in the first four to five years of their life makes a considerable impact on their ability to decode speech. The existence of these critical early language development stages may explain why, for instance, profoundly prelingually deaf children receiving a cochlear implant after age 7 show little central auditory development even years following implantation (Sharma et al., 2002). It also suggests that someone who has been profoundly deaf from birth should not be able to decode (or perhaps even recognise as such) speech “heard” in auditory hallucinations. However, as stated before, in cases where profound deafness was diagnosed quite late it is very difficult to establish whether a person is indeed profoundly “prelingually” deaf and has no hearing experience whatsoever.
Issues of communication:
Communicating with mentally distressed patients.
Bridging the communication gap between hearing researchers and deaf psychotic participants is not merely a straightforward matter of translating spoken language into sign language and vice-versa. In asking people about their experiences, the implicit general assumptions are that they understood the question correctly, are able to reflect on their internal states and recall their recent experiences accurately, and are able to express them in an understandable way. However this is rarely the case with someone who is experiencing a mental health crisis. Problems in communication, reasoning and suggestibility are a major issue with people who are distressed, confused, cognitively impaired or, as with psychosis, combinations of the above. So when a person suffering from psychosis is asked “Do you hear voices?” (a question only meaningfully understood in the context of Mental Health culture anyway), and they say “yes”, it cannot be taken for granted that they understood and considered the question in the correct context, and upon introspecting, recollecting and carefully weighing up their experiences, decided that, in all likelihood yes, they probably do.
Interpreting across modalities
Communication and suggestibility take on a deeper dimension where Deaf patients are concerned. How to translate “do you hear voices” or “do you have auditory hallucinations” into Sign Language correctly? As Vernon and Miller (2001) point out, when interpreting occurs not just between two languages, but between languages with different modalities - spoken and signed - the relationship between source and target texts can be even more complex. Sign language interpreters in mental health settings face extreme linguistic and cultural difficulties in interpreting the everyday language used in these settings. This is particularly true when deaf clients have limited English proficiency, which often requires interpreters to use expansion techniques in order to render messages successfully.
Written discussions about interpreting issues, or any issue of an exchange of concepts between users of different languages are notoriously difficult to present, being inevitably presented in at most one of those languages. Vernon and Miller admirably attempt to illustrate the difficulties, but they also demonstrate the real issue of presenting issues of sign language or sign language users’ conceptual lives in a different language (i.e. any written language). When they talk about “a sign or combination of signs, such as NERVOUS, SCARED, CRABBY, IRRITATED, or UPSET” they give the impression that, for example, the English word “NERVOUS” equates to a specific ASL sign. It does not. Just as “S’il vous plait” translates literally as “If it pleases you”, but is more accurately translated as simply “Please”, so signs and words only loosely correspond. As a result those two languages will not correspond in a comfortable word-for-word or word-for-sign relationship. Naïve second-language learners nevertheless assume such a relationship in order to assist learning, although fluency can only naturally arise as the conceptual world of that learner adjusts to accommodate the new language. Importantly sign language interpreters, as Vernon and Miller suggest, also retreat to this safer, though risky, strategy when assisting the clinical interview of psychotic deaf patients.
Thus:
when A puts into words what is intended.
an interpreter then puts into sign what was said and
B extracts meaning and supposed intention from the presented translated statement
and B then
considers a response, puts it into sign, and
that response is translated into words/speech and
A comes to some understanding of what was presented,
there are six points of potential misrepresentation and misunderstanding between A’s original intention and what he understands to be the response.
Interpreting and suggestibility
Some mentally healthy deaf people of normal ability may have difficulties with formal questions such as “how” and “why” even in BSL. Thacker (1991) suggests this may be because they are used to being told rather than asked. Also questions may have to be phrased in multiple-choice form, taking care not to lead or limit the subject too far and by presenting concrete examples. Recent research in a forensic setting (O’Rourke, 2004) suggests that in conversation with non-signing hearing people, the use of BSL interpreters could make deaf sign users more prone to suggestibility. In this respect we have observed that a sign often interpreted as “voice”, involving a mouth-like hand shape located near the ear, often appears after contact with Mental Health services, whereas before then signs used to describe hallucinatory experiences differ considerably.
Concepts of “hearing”:
When profoundly prelingually deaf people with psychosis report hearing voices, it is unlikely that they are referring to the same experience that hearing people with psychosis have, simply because they do not have the same framework for “hearing” as hearing people. Indeed in examining deaf psychotic patients’ reports of auditory hallucinations, Critchley et al. 1981 found that “exact subjective experiences were difficult to determine”. Some Deaf people with psychosis describe “voices” more as “ideas coming into one’s head” or as “the feeling of air brushing past the ears, like when someone speaks” while Thacker and Kinlocke (1997) as well as Fraunhofer and Kitson (reported in Kitson & Thacker, 2000) found that deaf people could describe their experience of auditory hallucinations in great detail, but whether this was akin to “hearing” in the conventional sense was impossible to say. One patient, who reported definitely hearing a voice through the ears, could identify that a person was “talking”, but not that person’s gender. The authors suggest that this may indicate that the experience is not a true auditory experience, in that properties like voice pitch and sound could not be described. However their conclusion may be too broad; what it appears to indicate is that deaf people cannot meaningfully or reliably describe their experience of “hearing voices” to hearing people.
However, it would be a mistake to think that Deaf people have no framework for “hearing” at all. As mentioned above, many deaf people may have some residual hearing, even if not sufficient for oral communication, and not every deaf person has been deaf from birth. Profoundly deaf people can still perceive the vibrations of sound. In this regard Thacker (1994) reported on a patient who described how her sister was “talking” (sign) to her in her abdomen, which was where in reality she sensed the vibration of loud sounds.
Moreover, even profoundly prelingually deaf people naturally have their own ideas and imagination of what “hearing” is like, just like hearing people have their own imaginary (simplistic) construct of what it is like to be deaf. Research has shown that profoundly prelingually deaf children develop phonological representations of words while learning to read, through the experience of lip reading, kinaesthetic feedback from one’s own throat during speech, cued speech and finger spelling. Each may provide information about the sound structure of words (Sterne & Goswami, 2000; Hanson et al., 1991) although phonological representations formed in this way are bound to be different from the hearing experience.
It seems then that, deaf or hearing, the human brain is predisposed to try and conceptualise “sound” in some way. This was alluded to by David Wright (1969) in his autobiography “Deafness”, when he described how he would find himself experiencing “sound-images projected by his mind onto his visually perceived environment as a function of visual cues”. Observing lip-reading or the wind moving leaves on a tree prompted the imagining of accompanying sound, which he referred to as “phantasmal voices” or “eye-music”. However, as Sachs (1989) points out, Wright was not deaf at birth and therefore had the experience of sound and speech as a basis for such mental associations, whereas a profoundly prelingually deaf person of course would not. Freimuth (2002) however points out that profoundly prelingually deaf people generally do not mention or complain about total silence in the same way that people blind from birth do not mention or complain about living in total darkness.
“I cannot speak for all deaf people, but I do not live in a silent world. All movement registers as sound in my mind, that is how I lip-read. The movement of the lips makes a sound, which I "hear". Seeing the trees moving in the wind or the waves lapping the shore make sounds to me.
Fluorescent lights that are on the blink are very irritating to me and also several other deaf people I know, because it is like being in a noisy room. I also find someone tapping a table or constantly moving their hands irritating for the same reason.”
(--posted on a Deaf forum)
Profoundly prelingually deaf people sometimes report dreams in which they communicate with other people through speech. However transfer of information is described as an almost “telepathic” process of “knowing” what was said, rather than having “heard” it (although what is meant by “not hearing” is as unknowable as what is meant by “hearing”). This has a striking similarity with findings mentioned above, that psychotic deaf patients who reported hearing voices could not describe the voice quality, i.e. pitch, tone, accent, volume or even necessarily the exact words being spoken, even though they “knew” what the voices said. Kitson & Fry (1990) suggest that the reports of Deaf mentally ill people hearing voices may not be so surprising, when one considers that deaf people do possess the concept of oral communication. Although they have not been exposed to the sound of voices, they do experience accompanying quality (i.e. behaviour, gesture, facial expression and posture), function, meaning and effect of this vocal communication either in terms of responses in others or in themselves. Moreover, 9 out of 10 deaf people are born to hearing parents, many of which do not learn to sign, and in the wider community only 1 person in 1000 communicates in Sign. As such the most frequent socially meaningful (although perhaps not directly content-meaningful) communications are in an oral/auditory modality, albeit inadequate and incomplete.
The delusion of hearing voices.
Psychosis is a heterogenous phenomenon: patients present with various affective symptoms and modalities of hallucination, paranoid or non-paranoid delusions, negative or positive symptom complexes, thought disorder, cognitive disturbance and agitation or apathy. So when someone is psychotic and, with a confused and distressed mind, and muddled-up frameworks, tries to make sense of their confusing experiences, could they conclude they are “hearing”?. In the aforementioned research by Du Feu and McKenna, some psychotic patients were reported to have developed the delusion that they had acquired hearing. This raises the interesting question as to where hallucination ends and delusion begins.
Whereas hallucinations reflect a direct experience of the aberrant salience of internal representations, delusions are a cognitive effort by the patient to make sense of these aberrantly salient experiences
Chadwick, Birchwood and Trower’s (1996) ABC analysis of auditory voice hallucinations comprise:
A – Activating Event (a voice experience)
B – Belief regarding that experience, and
C – Consequent behaviours or affect
The model supposes that beliefs about the voice are secondary delusions, and for a cognitive approach to therapy for such experiences this is an appropriate model. However, for prelingually profoundly deaf psychotic patients reporting voices, it ought also to be considered that the delusional component may rather be as follows:
A – Complex, inexplicable experience involving apparent reception of meaningful information
B – Belief that that experience may be the hearing of a voice
C – Consequent behaviours and affect (including reporting the hearing of voices when asked)
As suggested above, even though they may never have experienced it, deaf psychotic patients may be able to imagine what “hearing” is like. A parallel can be drawn with hearing psychotic patients who report sensory “perceptions” which have no physical antecedents either, such as feeling that electric rays are penetrating the body, or that satellites are transmitting radio waves into to their brain, or that they are possessed by an alien or spirit. This model provides a more useful framework for the experiences of many psychotic deaf people than one that simply asserts that they “hear voices. It provides a potential strategy for therapy, which, incidentally, can equally apply to hearing psychotic patients: it invites the patient to re-examine and make sense of what seems at first a confusing and possibly frightening experience.
Secondary gains
Then there are all the issues of mental health and Deafness, sick-roles and secondary gains. Given that the experience of mental illness is generally private, it is not available to direct objective examination. Rather, symptom reports and illness behaviour are evaluated through a complex assessment of their impact and function in the patient’s life. As human social contexts have become more complex through history, so have the accommodations and allowances made for sick and disabled members of society. As such criteria for legitimate entry to the sick role have evolved, with modern society placing heavy emphasis on demonstrated tissue damage or organic malfunction, or severe mental distress as demonstrated through ratified psychiatric criteria. Due to the communication barrier, deaf people find it notoriously difficult to access services in times of distress and feel easily isolated. The powerful reassurance of a professional taking notice of, and making apparent sense of what seems a baffling and frightening experience is perhaps not to be underestimated.
Conclusion: shifting the frames of reference
Church (1961) conceptualises the senses as “units of perception”. They are a composition of the sensory stimulus input and the interpretation/identification of that stimulus input. Interaction and communication with other people plays an important role in this, as it establishes a consensus of concepts and frameworks within which stimuli are interpreted and identified. Therefore perception units work in both directions; they form the basis for making sense of our impressions of the world, but also offer a shared framework by which we communicate these impressions to others in a meaningful way. Because their sensory experiences are different, profoundly deaf people and hearing people are unable to establish shared concepts and frameworks around the experience of hearing and sound. In that case, a hearing person cannot ask a deaf person any meaningful question about an aural sensory experience, such as “Do you hear voices”, and a deaf person cannot reply in a way that is meaningful to a hearing person.
In that case, why do we regard everything that a deaf psychotic patient reports with extreme scepticism, but not their counter-intuitive reports of hearing voices? Because we know that some hearing psychotic patients report hearing voices. It fits the hearing expectations despite its evidently paradoxical nature. Also, just as there still is a tendency for delusions to be dismissed as meaningless products of a confused mind (Berrios, 1991; Aschebrock 2003), rather than as experiences meaningful to the psychotic patient as attempts to make sense of their environment or of internal psychological conflict, so do we fail to appreciate the unique deaf psychotic experience as meaningful within their deaf frames of reference.
For instance, even in the aforementioned research by Du Feu & McKenna (1999), where one of the researchers had an acquired hearing impairment herself and had some experience in using sign language, a structured psychiatric interview standardised on hearing patients and devised according to symptom presentation and clustering of hearing subjects, was employed. Similarly researchers generally use psychiatric diagnostic criteria developed with hearing patients. However Evans & Elliott (1981) for instance expand on e.g. the misdiagnosis of psychotic thought disorder in deaf patients who have a fundamentally different way of communicating, and how the expression of emotions in gesture and action rather than spoken word or tone of voice can be misinterpreted as affect lability or impulsiveness.
This bias seems unavoidable. All scientific literature is written, and as such represents a philosophy of science, conjecture, hypothesis-testing, categorisation, deduction and induction from a hearing perspective (British and American Sign Languages, and possibly all others, have no written form). As a result it may quite reasonably be seen to be culturally hearing. Models of wellness and illness, symptom-clustering yielding diagnostic nosologies, treatment strategies and all aspects of mental health work may also therefore be meaningfully understood as culturally hearing. In addition, this cultural bias remains almost entirely unnoticed (though not unimportant) when those working within these models and on the basis of this literature are themselves hearing. Just as we think it is the others with the accent, so are we unable to perceive this hearing cultural bias. Just as our native language-development in the early years tunes our perceptions to the language in which we are embedded, and away from other languages’ phonetic forms, so it becomes extremely difficult for inevitably culturally hearing mental health workers (whether themselves audiologically hearing or deaf) to notice the biases and distortions inevitable in the culturally hearing fields of psychology and psychiatry.
When a (culturally) hearing professional converses with a deaf psychotic patient about auditory phenomena that are grounded in this complex statistical analysis of symptom presentation in hearing people and a culture of academic psychiatry, it is easy to imagine to what (a great) extent weak links in the chain of communication can detrimentally influence the discussion.
When deaf psychotic patients report “hearing voices”, they undoubtedly are experiencing something. Just what that is however, is not known. Moreover, hearing mental health professionals may have to come to terms with the fact that they most likely will never be able to know; that this experience is unknowable, because they do not share deaf phenomenological frames of reference. The only mental health professionals, who may be able to make sense of these experiences, are prelingually profoundly deaf mental health professionals –provided that they are able to extricate themselves from the cultural “hearingness” of the field.
However understanding the modality of the hallucination does not have to be essential in helping a deaf psychotic patient manage these hallucinatory experiences. Indeed it may be more clinically adaptive to actively acknowledge that this is not known. Many relatively healthy and undisturbed hearing people hear voices (e.g. Romme and Escher, 1992) but do not necessarily feel bothered by them, or impaired in their daily life functioning. In psychosis also, it is not the modality of the hallucinations that is a problem, or even the presence of hallucinations in itself; it is their perceived meaning and psychological impact that appear to matter (Chadwick & Birchwood, 1994). The distress they generate, and the delusional beliefs that are formed in an attempt to make sense of them may serve to maintain them (e.g. Beck & Rector, 2003). As such effective interventions aimed at managing hallucinations tend to concentrate on changing their perceived meaning and reducing their distressing impact.
In deaf psychotic patients also, regardless of the question of modality, the meaning and function of their hallucinations appears to remain the same. They still have content and meaning, they still generate thoughts and feelings in the patient who may or may not be distressed by them, and who may or may not feel compelled to act on them. In terms of these dimensions, deaf and hearing people appear to share the same frames of reference. Therefore it is possible that deaf psychotic patients can be helped to manage their hallucinations in terms of the meanings they assign to them the level of control they experience over them and the distress that they generate. Whether the same strategies that have been developed for hearing psychotic patients are effective in managing the deaf hallucinatory experience however, like all aspects of deaf mental health, needs not to be assumed but to be explored.
References:
Aschebrock, Y., Gavey, N., McCreanor, T., and Tippett, L. (2003) Is the content of delusions and hallucinations important? Australasian Psychiatry 11(3):306-311
Beck, A.T. & Rector, N A. (2003) A Cognitive Model of Hallucinations. Cognitive Therapy & Research 27(1):19-52
Berrios G. (1991) Delusions as “wrong beliefs”: a conceptual history. British Journal of Psychiatry 159: 6-13
Chadwick P. and Birchwood M.J. (1994) The omnipotence of voices: a cognitive approach to auditory hallucinations. British Journal of Psychiatry 164: 190-201
Chadwick P., Birchwood M.J. and Trower P. (1996) Cognitive Therapy for delusions, voices and paranoia”. London: Wiley
Church, Joseph (1961) language and the Discovery of Reality: a Developmental Psychology of Cognition. New York: Random House
Critchley E.M., Denmark J.C., Warren F. and Wilson K.A. (1981) Hallucinatory experiences of prelingually profoundly deaf schizophrenics. British Journal of Psychiatry 138: 30-32
du Feu M & McKenna P.J. (1999) Prelingually profoundly deaf schizophrenic patients who hear voices: a phenomenological analysis. Acta Psychiatrica Scandinavia 99(6): 453-459
Evans J.W. & Eliot H. (1981) Screening criteria for the diagnosis of schizophrenia in deaf patients. Archives of General Psychiatry 38(7): 787-790
Kitson N. and Thacker A. (2000) Adult Psychiatry: Assessment in: Hindley P. and Kitson N. (eds). Mental Health and Deafness. London: Whurr.
Freimuth C. (2002) Was ‚hört‘ ein Mensch, der nicht hören kann? Das Zeichen‘, Zeitschrift für Sprache und Kultur Gehörloser 60(16): 1-16
Hanson Goodell & Perfetti (1991) Tongue-twister effects in the silent reading of hearing and deaf college students. Journal of Memory & Language 30: 319-330
Kitson N. & Fry R. (1990) Prelingual deafness and Psychiatry. British Journal of Hospital Medicine 44: 353-356
Kuhl, P., Williams, K. A., Lacerda, F., Stevens, K. N., & Lindblom, B. (1992) Linguistic experience alters phonetic perception in infants by six months of age. Science 255: 606-608
O’Rourke S. (2004) Access to the Criminal Justice System: Suggestibility and deafness. Presentation at the BSMHD 2004 Annual Conference, Cardiff.
Preciado D.A., Lim L.H.Y., Cohen A.P., Madden C, Myer D, Ngo C, Bradshaw J.K., Lawson L., Choo D.I., Greinwald Jr J.H. (2004) A diagnostic paradigm for childhood idiopathic sensorineural hearing loss. Otolaryngology -Head and Neck Surgery 131(6): 804-809
Romme M. and Escher S. (1992) Accepting Voices. London: MIND Publications.
Sachs O. (1989) Seeing Voices. London: Picador.
Schonauer K., Achtergarde D., Gotthardt U. and Folkerts H.W. (1998) Hallucinatory modalities in prelingually deaf schizophrenic patients: a retrospective analysis of 67 cases. Acta Psychiatrica Scandinavia 98(5): 377-383
Sharma A., Dorman M.F. and Spahr A.J. (2002) A sensitive period for the development of the central auditory system in children with cochlear implants: implications for age of implantation. Ear Hear 23(6):532-9
Sterne A. and Goswami U.C. (2000) Phonological awareness of syllables, onset-rime units and phonemes in deaf children. Journal of Child Psychology & Psychiatry & Allied Disciplines 41(5): 609-626
Thacker A. (1991) Communication: disorder, deprivation or discrimination? Proceedings of the Inaugural Conference of the British Society on Mental Health and Deafness. London.
Thacker, A. J. (1994) Formal communication disorder. Sign language in deaf people with schizophrenia. British Journal of Psychiatry 165: 818–823
Thacker and Kinlocke (1997)
Vernon M. and Miller K. (2001) Interpreting in Mental Health Settings: Issues and Concerns. American Annals of the Deaf 146(5): 420-434.
Wright D. (1969) Deafness. London, Allen lane.
