Develop. Med. Child Neurol. 1969,11,561-568

Differential Diagnosis of Impaired Hearing in Children

Kevin Murphy

OBSERVATIONS about auditory function are in fact extrapolations from response pat- terns. Such patterns may be measured or recorded subjectively or objectively. Audi- tory response occurs when stimuli have been transmitted to the brain-stem via the auditory mechanism. Responses are ‘any change in state or activity which is signific- antly related to a stimulus’. Hence changes in heart rate, excretion of adrenaline, modification of electrodermal impedance, etc, can all be described as auditory responses when it is certain that audio- frequency stimuli have been detected by the peripheral auditory mechanism and that the reaction-time falls within normal limits or satisfies other consistency criteria.

Responses to sound may not necessarily indicate hearing. Though hearing is one form of auditory response, not all forms of auditory response are hearing. The term ‘hearing’ predicates a pathway involving the cochlea, the eighth nerve, brain-stem and primary auditory area of the cortex. It is now known that hearing can take place and that indices of audio-cortical function can be measured in the presence of severe language disorder. In other words, one stage further than the primary auditory area of the cortex must be involved in language acquisition.

Maturational Factors For these reasons, the researches of

Murphy and Smyth (1962) on fetal audio- frequency stimulation cannot be described as tests of fetal hearing. If the term ‘hear- ing’ depends on audio-cortical functioning the clearest index of its presence will be some adaptive behaviour relating to auditory response. Selective control of startle is suggested as one early criterion.

Maturation of response patterns accom- panies maturation of neuromotor function, and at the Audiology Research Unit in Reading, Berkshire, techniques have been evolved, using the Papousek cradle (Pap- ousek 1961), which facilitate auditory orienting response in the first few minutes of life. (The results of this research will be described in detail in another paper.) As the normal infant reaches the end of the first week of life there is a generalised diminution of sensory function. This is followed by the emergence of a sensory hierarchy; the ‘blocking’ effect of visual attention in the first six to eight months of life is commonly acknowledged. The con- cept of auditory attention in infants is less commonly discussed in the literature, though this concept is basic to the study of listening. Some recent experiments in auditory attention in infants suggest that

Audiology Unit, Royal Berkshire Hospital, Reading, Berks.

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though this factor is subject to environmen- tal modification there is a predictable pattern of auditory attention which varies with age, condition and experience.

Modifications of auditory attention des- cribed as resulting from minor impair- ments of hearing are normally regarded as being relatively temporary. Recent work on young children in Reading in which peripheral auditory function is restored from moderately severe loss indi- cates that for a few children a lengthy period of training is required before auditory attention develops. In some cases, though peripheral auditory function appears to be normal at a primitive level, auditory learning may be slow to develop and auditory discrimination of speech may require continued therapy.

Psycho-social Aspects of Hearing Since auditory function modifies vocal

communication it may be described as an adjunct of human functioning essential to complete social well-being. It is also axio- matic that social well-being relates to the total social environment. In other words, auditory function promotes the well-being of the infant with respect to the rest of the immediate social community, particularly the parents and more consistently the mother, in those cultures where the mother takes the major part in the care of the infant.

It is only too easy to regard auditory function as completely physiological and to concentrate attention on the indices of maturation of cortical control while ignor- ing the social-emotional aspects which accompany such development. For in- stance, if we turn our attention to fetal auditory response and to the intrauterine reverberations produced by maternal speech we are immediately faced with the possibility of prenatal auditory experience of the speech frequencies. (The significance of this kind of experience,

hitherto unique in humans, may well emerge from the new techniques of intrau- terine audio-frequency stimulation, which a number of us are currently investigating in animals.)

The healthy infant produces a different pattern of evolution of response to sound from that of the immature or unhealthy infant. Infants recovering from various forms of birth trauma have a persistent hyper-responsiveness to all sensory stimuli, particularly auditory stimuli. The short- gestation, postmature, anoxic or brain- damaged infant persists in hyper-respon- siveness to all sound, whereas the healthy infant passes through apattern of behaviour which seems to indicate some form of information storage and organisation. This pattern may well be two aspects of the same phenomenon of organisation, and is characterised by a primitive form of selec- tivity followed by the emergence of a clearer system of learning leading to a developed pattern of experience. The term ‘selectivity’ is used to describe the phenom- enon in which the normal infant aged three to six weeks ceases to respond to sounds consistently present in the environ- ment while responding, often with startle or distress, to uncommon sounds even at significantly lower intensities. Following on this pattern, the second aspect of organisation occurs, namely, recognition and prediction. In this phenomenon con- tentment occurs when the pattern remains unchanged and distress when the auditory environment is radically changed in the first two or three months of life. This aspect of infant care could become a more positive part of our advice to parents who are bringing their infants into the domestic environment after prolonged periods of hospitalisation in the early days or weeks of life.

Anxious parents bring their children to us with an alleged deafness because they see the maturation process described above.

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Many mothers, particularly those without much previous experience of infants, be- come anxious when their healthy infant with quite normal hearing sleeps placidly through the noisiest of domestic environ- ments. Similarly, when testing immature infants, one must assess the extent to which their hyper-responsiveness is height- ened by domestic care. Visiting such homes one sees a careful exclusion of noise; parents tip-toe around the house, whisper- ing, turning down the radio, closing win- dows and effectively depriving their infant of important aspects of auditory accom- modation and social experience.

Much of the early work on auditory test- ing, pioneered by the Ewings (1944), was based on the development of auditory experience as one aspect of the child’s total experience. Dealing with children aged one year or older, Irene Ewing saw that familiar domestic noises were related to general experience and used such noises to provoke the child into a social response relevant to a social situation. In my own researches, in common with such other workers as Fisch (1967), Sheridan (1958), Whetnall ( I 964), Di Carlo (1962), Kendall ( I 964) etc., it has become clear that familiar noises out of context may well be ignored by young infants (i.e., from birth up to six or eight months), whereas unfamiliar noises tend to evoke response with greater con- sistency. There is one exception to this particular comment which I feel is of considerable importance. Using an eight- month-old child, I have often demonstrated to students that the mother’s voice whisper- ing the child’s name will evoke response when a female colleague’s voice at the same intensity whispering the same name may be consistently ignored. Similarly, the infant is normally presented with a series of sounds similar to his name which he ignores until his name occurs. One eight- month infant named ‘Barry’ ignored ‘Garry’, ‘Harry’, ‘Larry’ and ‘Tarry’, but

turned and smiled to his name, the whole sequence being presented at the same intensity by means of a tape recorder and amplifier.

Vocalisation From the fifth month forward, vocalisa-

tion can often be evoked in the infant with normal hearing by auditory stimulation. Using dolls or dolls’ faces as the apparent sound source one has evoked babble in some infants in apparent response to auditory stimuli. In certain infants if the stimuli have been sufficiently distinct (in the series I am describing these were a 500 C.P.S. pure tone and a 4,000 C.P.S. tone presented a t 50 dbs. above normal thres- hold at the ear) the infant responded by articulating sounds like the two tones pre- sented. Similarly an excellent test of the integrity of the audio-vocal mechanism is the presentation of a sequence of vocalisa- tions to an infant from which a vocal response is often evoked. Sometimes these patterns culminate in vocalisations which the mother states have not been produced by the infant before the experiment. Audio-vocal shaping as a diagnostic pro- cedure merits careful study and validation.

Modifiers of Auditory Responses Earlier in this paper I describe the use

of the mother’s voice, familiar and un- familiar sounds and environmental experi- ences. Inherent in these comments is the hypothesis that responses are indicative of some coding activity in the infant which is auditory in character. Other aspects of the organisation of sensory function merit description. Certain factors militate against auditory response, especially when intensi- ties below startle threshold are being used. For instance, the infant of three to five months is unlikely to respond to stimuli below 50 dbs. (reference normal threshold) if he is uncomfortable because of ab- dominal distension, because he needs his

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diaper changing, or because he has been recently fed. Below the age of eight months, the infant who is deeply involved visually is unlikely to respond to auditory stimuli; this behaviour is so consistent in infants that visual dominance after the age of eight to nine months is regarded as a possible criterion of immaturity to be evaluated in the total record. At the same time use can be made of visual dominance by giving visual re-inforcement to success- ful auditory function (tracking,conditioned tapping of visible displays, etc.). For in- stance, a simple device developed by the Scientific Officer in the Audiology Re- search Unit at Reading illuminates the re- flection of the infant’s face in a mirror when he successfully localises a sound presented at the level of and in line with either ear.

Significance of Inconsistent Responses Inconsistent responses tend to occur in

children who are grossly immature, intell- ectually severely retarded, brain-damaged, hyperkinetic, or who suffer from some high brain-stem disorder which precludes auditory coding, or from some condition which minimises consistent auditory ex- perience. For instance, the child with mild hearing impairment appears to suffer from a disability compounded from his modified threshold and from his modified experience of sound. In this respect his ability to listen or to attend is modified as well as his ability to hear. The experience in our unit is that it is a consistent pattern for children suffering from relatively mild conductive losses to continue behaving as though they have a hearing impairment when in fact their threshold has been returned to normal by surgical procedures. This interesting phenomenon usually re- mits in two to three weeks, except in the cases described earlier in this paper, or where the child has decided for psycho- social reasons that some mild hearing

impairment is useful to his life! Similarly, children suffering from fluctuating conduc- tive loss are often described by their parents or teachers as ‘naughty’, ‘stupid’ or ‘inattentive’, because consistent and continuous attention to heard sound is significantly modified.

Auditory response is subject to consider- able modification by the previous psycho- social experience of the individual. Modi- fied auditory attention may occur for many reasons, with some of which psychiatrists will be familiar. There are two research findings which merit consideration. In a project designed to investigate the effect of distance on the modification of response, infants aged six months tended to ignore sounds produced at distances greater than six feet under reverberent laboratory con- ditions. We concluded that stimuli overlaid with background noise (in this case echo of the present stimulus) will be ignored by infants if that background noise approxi- mates the stimulus too closely in frequency and intensity. This seems to imply that even by six months the infant has some kind of pre-scanning mechanism, which decides on the direction of attention-in this case, in terms of discrimination of a figure-ground relationship.

In a second experiment, groups of students were given cups of tea and a general level of conversation allowed to develop. In the middle of this conversation two stimulus sentences were presented by a tape-recorder and amplifier at the same sound-pressure level (45 db.). These two sentences were: ‘Who’d like another drink?’ and ‘Who‘s going to wash up?’. To the first sentence 21 out of 24 replied. To the second, 3 replied. The attention of the group was then secured and both sentences were repeated, when all 24 subjects said they had heard both sentences. When conversation developed again, the sentences were replayed in reverse order. This time 5 said they had heard the

sentence ‘Who’s going to wash up?’ and 21 ‘Who’d like another drink?’. In normal conversation, the phenomenon I have just described would be called ‘listening.’ Listening is defined more clearly as the ability to attend to heard sound for pur- poses of interpretation, the term ‘interpre- tation’ being used here to describe all elements of assessment of an informational or emotional character.

Modified listening skill is sometimes met in patients with modified intellectual skills, modified mental health, modified peri- pheral hearing or modified auditory coding. I t is important therefore to differentiate between these conditions. The situation is confused by the fact that hearing is basic to the maturation of spoken language and that modified spoken language leads to a variety of stresses, two of which merit close consideration. (1) Hearing has a com- munication function before the develop- ment of full language skill. By this, I mean that hearing facilitates self-monitoring. (2) Hearing facilitates environmental monitor- ing. Thus, the child can be self-aware and socially aware, can discriminate between self and others, and can became aware of self within the community, an extension of body-image to social-image.

Modification of the developing skill of listening may, in company with other stresses, lead to disastrous consequences for the child, preventing the self-awareness described above, preventing learning, modi- fying the maturation of systematic person- to-person contact.

Diagnosis

certain questions, as follows : ( I ) Is auditory response present ?

The presence of auditory response is assessed by stimulating the child in varying intensities and observing the changes in his activity. Changes of state can be evoked in the presence of high brain-stem lesions.

Diagnosis, therefore, attempts to answer

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(I was able to illustrate head turning in an anencephalic infant two days old in re- sponse to pure and complex tones of the order of 40 dbs. Post-mortem studies of this infant showed destruction of the brain- stem which the pathologist described as extending to the approximate level of the pons). In other words, head turning for sound may indicate auditory function involving only the cochlear nuclei.

( 2 ) Is auditory identification present ? The assessment of auditory identification

involves two criteria. Firstly, describing the spectrum of reliable stimuli (some patients will respond consistently to pure and complex tones, but not to voice). Secondly, detection, audio-visual coding. This consists of presenting sounds sequen- tially from two or three different devices until the child shows that he has identified the device which produces the sound. The three objects might be a bell, a rattle and a squeaky toy. When the child has finished investigating each toy in turn, he is pre- sented with a tape recording of the sound of the toys and by one year of age will normally reach for the toy which he associates with the sound.

( 3 ) Is response to voice present ? Cues are presented based on the patient’s

own name or the name ‘Mummy’, ‘Daddy’, ‘Nana’-if they are present-or possibly on simple domestic cues. ‘Where’s Teddy’ etc All of these may be presented in free field by calibrated amplifiers so that some idea of the probable threshold may be reached. Our procedure makes use of an amplifier and induction loop, within the field of which small dolls containing induc- tion coils, amplifiers and loud-speakers are placed. These dolls, being free from any wires, attract the continued attention of the child and facilitate conversation at con- trolled output levels. A system derived from our own is more fully described elsewhere.

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(4) Can auditory conditioning be achieved? If all these investigations prove satisfac-

tory and the patient is mature enough in age or intelligence, other verbal instruc- tions may be tried as a basis for general conditioning. Following the satisfactory establishment of general conditioning, auditory conditioning is attempted. Where visual or tactile conditioning is practicable but auditory conditioning is not, some modification of auditory function may well exist and the child will be kept under regular review until it is clear that there is no modification of audio-visual organisa- tion or no danger of modified language reception.

Differential Diagnosis The major areas of error in differential

diagnosis spring from many factors, in- cluding the following: (1) The tester forgets that he is dealing

with a human subject and treats the child as though he were a pair of perambulating ears.

(2) The tester forgets that many patients do not like hospitals, do not like strangers and do not like noises which have no predictability or real meaning.

(3) Disturbed patients, immature patients or patients with certain hearing dis- orders respond with considerable vari- ability of consistency.

(4) Some children with modified auditory attention are extremely vulnerable to a huge variety of distractions, particu- larly those arising from the visual field

and more particularly from the peri- pheral visual field.

( 5 ) Auditory response is variably adaptive. Some children will disregard the second presentation of a stimulus, so that one has initially to decide whether the first response was coincidence. In fact, with young children, disturbed children, subnormal children and brain-damaged children it is a wise precaution to use sequences of single distinct stimuli.

(6) Such conditions as retro-cochlear le- sions permit response to the onset or cessation of a stimulus without facilita- ting transmission of a discernable audi- tory pattern between these two events.

(7) Most of us are interested in a child's ability to use his hearing for language learning or for general social monitor- ing. Auditory response, particularly to pure and complex tones, may be no guide to these skills and it is necessary to look beyond response. For these reasons, the wide variety of objective tests-Audio, EEG, Stapes Impedance Audiometry, Audio-Vasculometry and psycho-gaivanic audiometry-may well indicate auditory response, but do not give us enough information to say that hearing is present or that listening is occurring at a level which would facilitate language acquisition. Differ- ential diagnosis begins with a clarifica- tion of terminology and proceeds via an assessment of response to a clearer investigation of cortical organisation of auditory cues in relation to the total behaviour pattern of the child.

SUMMARY Hearing and listening are differentiated from each other and from other aspects of

auditory response. Auditory behaviour is described in terms of its physiological implications and its subjective and objective correlates. Emphasis on the developmental nature of auditory behaviour is made by reviewing the influence of maturational psycho-social and pathological factors. Some of the consequences of auditory dysfunction are described particularly in their relevance to differential diagnosis, and the criteria for assessing auditory

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function are given. Sources of diagnostic error are described, which may arise from factors in the child or from factors in the observer. Since auditory function is inferred from auditory behaviour it is stressed that diagnosis of auditory function is liable to many of the errors inherent in all behavioural studies.

R ~ S U M ~ Diagnostic diffkrentiel des dkfauts d’audition chez les enfants

Entendre et Ccouter sont difftrenciks I’un de l’autre et d’autres aspects de la rCponse auditive. Le comportement auditif est dtcrit en termes de ses implications physiologiques et de ses caracttres subjectif et objectif.

L’attention est portte sur la nature gtnetique du comportement auditif en revoyant I’influence des diffkrente facteurs, de maturation, psychosociaux et pathologiques.

Quelques unes des constquences des troubles de l’audition sont dCcrites, spkcialement dans leur relation avec un diagnostic difftrentiel et les critkes d’apprtciation de la fonction auditive sont donnts.

Les sources d’erreur de diagnostic sont Cgalement analystes aussi bien celles qui reltvent de l’enfant que celles qui relbvent de l’observateur.

Puisque la fonction auditive est dtduite du comportement auditif, on peut penser que le diagnostic de la fonction auditive est marque des nombreus eserreurs inherentes A toute Ctude de comportement.

ZUSAMMENFASSUNG

Diyerentialdiagnose von Horstorungen bei Kindern Horen ist von Zuhoren und von anderen Gehorsqualitaten zu unterscheiden. Das

Verhalten des Gehors wird nach physiologischen Gesichtspunkten und nach seinem subjektiven und objektiven Ausdruck bewertet. Es wird in besonderem MaBe die Entwick- lung des Gehors unter dem EinfluB von Wachstums psychosozialen und pathologischen Faktoren beriicksichtigt. Es werden einige Konsequenzen beschrieben, die sich aus einer Gehorsdysfunktion ergeben und die besonders differentialdiagnostisch von Bedeutung sind, und es werden Kriterien angegeben, nach denen die Gehorsfunktion zu beurteilen ist. Ursachen diagnostischer Irrtiimer, die sowohl vonseiten des Kindes als auch vonseiten des Untersuchers entstehen konnen, werden beschrieben. Da die Gehorsfunktion vom Gehorsverhalten abhangt, wird betont, daB die Diagnose der Horleistung mit vielen Fehlern behaftet ist, die bei allen Verhaltensstudien vorkommen konnen.

RESUMEN

El diagnostico diferencial de la audicidn irnperfecta en 10s niiios Se diferencian la audicion y la escucha, ademis de otros tipos de respuesta auditiva. Se

describe la conducta auditiva con referencia a sus implicaciones fisiologicas y a sus corre- lativos subjetivos y objetivos. Se destaca la asociacion de la conducta auditiva al desarrollo por medio de comentar la influencia de factores madurativos psicosociales y patologicos. Se describen algunas de las consecuencias de una disfuncion auditiva, especialmente las que son importantes para el diagnostic0 diferencial, y se dan 10s criterios para valorar la funcion auditiva. Se describen unas causas de errores diagndsticos, que nacen de factores en el niiio o en el observador. Puesto que la funcion auditiva se infiere de la conducta auditiva, es claro que el diagnostico de la funcion auditiva es susceptible de 10s errores que son inherentes en todo estudio de conducta.

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REFEXENCES di Carlo, L. M., Kendall, D. C., Goldstein. R. (1962) ‘Diagnostic procedures for auditory disorders in

Eisenberg, R. B., Griffin, J., Coursin, D. B., Hunter, M. H. (1964) ‘Auditory behaviour in the human

Ewing, I. R., Ewing. A. W. G. (1944) ‘Ascertainment of deafness in early infancy and childhood.’ J. Luryng.,

Fisch, L. (1957) ‘The importance of auditory communication.’ Arch. Dis. Childh.. 32, 230. Kendall, D. C. (1964) ‘Pediatrics and disorders in communication. 111. The audiological examination of

Lenneberg, E. H. (1967) Biological Foundations of Language. New York: John Wiley. Murphy, K. P., Smyth. C. N. (1962) ‘Response of foetus to auditory stimulation.’ Lancet, i, 972. Papousek. H. (1961) ‘Conditioned head rotation reflexes in infants in the first months of Life.’ Acta puediar.

Sheridan, M. D. (1958) ‘Simple hearing tests for very young or mentally retarded children.’ Brit. med. J.

Whetnall, E., Fry, D. B. (1964) The Deaf Child. London : Heinemann.

children.’ Foliu phoniut., 14, 206.

neonate: a preliminary report.’ J. Speech Res., 7 , 245.

59, 309.

young children.’ Voltu Rev.. 66, 734

(Uppsulu), 50, 565.

ii, 999.

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