Central Auditory Disorders and Developmental Aphasia: Is There a Difference? Jon Eisenson

Central Auditory Disorders and Developmental Aphasia: Is There a Difference? Jon Eisenson In the first stage of preparation for this paper, I set Even in the absence of firm definitions, the members out to find "hard" definitions for central auditory process of our related professions including those of us who are ing, central auditory disorders, and, in keeping with the audiologists, hearing and speech scientists, speech/lan title, developmental aphasia. The search led me in several guage pathologists (I much prefer speech/language clini directions, occasionally into cul-de-sac lanes, sometimes cians), and pediatric neurologists have been neither along pleasant and nostalgic roads. Every so often, I felt modest nor negligent in devising tests and procedures for much like the legendary horseman who all at once rode the assessment of central auditory processing deficits in off into all possible directions. But firm definitions were children. Some of these are adaptations of approaches elusive. I found myself involved with points of view, mostly used with adults. Keith (1981), in his edited symposium negative, of minimal brain dysfunction, whether or not the Central Auditory and Language Disorders in Children, damage was minimal and the dysfunction appreciable; included numerous references as well as negative precau and in keeping with my own biases, explanations of prob tions on the evaluation of central auditory disorders. lems in reading when the teaching method required audi More recently, Berick et al. (1984) reviewed some of the tory intake and auditory processing for the decoding of a better known tests and procedures. Central auditory visual display. The names of Wernicke and Luria and their function is also a subject of study in dysfluent speech (Hall assumptions about the auditory area of the cortex and & Jerger, 1978; Wynne& Boehmler, 1982).1 assume that phonetic discrimination were recurrent. More recent ref earlier studies of delayed feedback in stutterers and the erences were to psycho neurological learning disabilities effect of masking noise on fluency were also concerned as well as to psychological learning deficits. Sometimes with aspects of central auditory functioning and dysfunc the difference between the two escaped me. tioning. For entirely personal reasons, I had little difficulty in In a chapter on "Neurologically Based Disorders", arriving at satisfactory definitions of congenital aphasia James Hardy (1978) devoted three pages to discussion and developmental aphasia. At the moment I do not raise that negates notions of minimal brain dysfunction and any question about the possibility of a difference. Person developmental aphasia as either viable or particularly ally, I go along with what Eimas (1979) offered as a work useful diagnostic entities. Nevertheless, albeit reluctantly, ing (operational) definition of central auditory disorders. Hardy did consider the possibility that there are children Eimas referred to " ... deficiencies in the ability to perceive who may have developmental auditory agnosia and per sounds of speech categorically, to analyze and code haps even developmental auditory aphasia. Hardy des speech in terms of a phonetic feature code, and to appre cribes a six-year-old boy who had normal hearing sensitiv ciate and utilize contextual information." Such deficien ity when tested with pure tone audiometry, but who could cies, Eimas noted, " ... may be functionally related to the not be tested with speech stimuli. The boy rejected the development of language disorders other than those speech signals and would not respond to them. The rejec tion itself is diagnostic. The boy's speech output was associated with reading disabilities." On the positive side, I like to think of central auditory processing much along wholly unintelligible and consisted of combinations of the line of Lasky & Katz (1983) as the way our central tones and noises. His intonation patterns resembled mechanisms receive, perceive, decode and utilize those of questions and possible attempts at explanations. The child scored no better than chance on language test speech·sound signals. It is how and what we do with the speech signals our hearing mechanisms respond to and items presented orally but scored at age level on intelli our central mechanisms select for listening and respond gence test items not calling for oral/aural communication. ing. At this point we have the implied distinction between As a possible partial explanation of the boy's difficulties, hearing and listening. Hardy suggested the likelihood of "Difficulty in analysis of the sequencing of the language code." Perhaps we cannot provide a firm definition of what Hardy appears to be a spokesman for many of our we are talking about any more than we are likely to find a colleagues who are reluctant to accept either the notion firm definition of cognition. This minor weakness has not of a central auditory disorder or of developmental aphasia prevented the propagation of courses, books, and except, possibly. when the evaluation includes clear, advanced degrees in cognitive psychology. "hard" neurological evidence to confirm brain damage. The arguments are coldly logical rather than psychologi Jon Eisenson, Ph.D. cal. Hardy does not accept diagnostic classification of a Emeritus Professor Hearing and Speech Science problem by a process of elimination. He and his col Stanford University leagues hold that mislearning related to inattention may be basic to communicative disabilities and that "The child Human Cammunication Canada/Communication Humaine Canada, Vol. 9, No. 4, 1985 13 may not have learned to attend well enough to discrimi there is, it may only be one of preference for terms or of nate among the acoustic patterns of speech" (Hardy, degree of impairment. My preference is developmental 1978). This line of argument has several weaknesses. aphasia. It is a disorder in which the primary impairment First, in the early months of life, surely without being is the processing (decoding and in turn encoding) of oral taught, normal infants show differential responses to language when the symbol-signals are presented at a speech and nonspeech signals as well as an ability to normal rate and not in excessive quantity_ If this sounds respond differentially to phonemes with minimal distinc familiar, it is intentional. Processing impairments are evi tive feature differences. They need only opportunity and dent in children who are "brain different" either because do not require teaching to attend to speech and to show of pre-natal or congenital brain damage, or because of evidence that speech is a human species-specific behav retarded or asynchronous maturation of the regions of ior. The position that, because young brains are endowed the brain involved in speech processing or association with plasticity for control of language functions, only between critical areas. For reasons considered earlier, I bilateral damage to the auditory centers should produce do not need to discuss the possibility that developmen dysfunctions such as auditory agnosia and congenital tally aphasic children may not have learned to be attentive aphasia is not persuasive. to speaking persons, or worse, somehow learned to be My concept of cerebral plasticity explains how a inattentive. The drive to hear and to listen is so powerful function, once established and to some degree shared by that the only possibility we need to entertain is that a rare centers in both hemispheres, in the event of damage to few children may stop listening because they have learned one hemisphere cent er for that particular function, may language and the aversive ways of some speakers in their come under the dominant control of the other hemis use and abuse of langauge. Until these rare children learn phere.lnitially, we need all the mechanisms with which we when and why they should not listen, and conversely elect are born to establish a function normally and naturally. to be mute, the human species-specific drive for language Further, it is possible that our newer techniques for learning is likely to dominate the behavior of potentially determining brain function and/or damage may soon normal children. provide us with information as to how individual brains Children with developmental aphasia may be pre are organized and how disorganization is related to corti sumed to show the following: adequate intelligence when cal, subcortical, and possibly subcerebral systems. It may assessed with non-language measures and adequate turn out that we have been looking where it was easy and hearing when assessed, however inadequately, by usual convenient to look and our looking and seeing may have audiometric procedures. They usually do not show early been limited to the instruments and prejudgements we evidence of emotional disturbances and of non-relating chose based on our expectations of what and where we problems and, therefore, should not be confused with would find what we were looking for. children with primary autism. Developmentally aphasic I believe that not enough of our colleagues have been children are almost always born into families whose sufficiently impressed with the reality that almost all hear members are themselves normal speakers and who try to ing children learn to speak without being directly taught. provide normal stimulation and opportunities for listening Even children with demonstrated articulatory apraxia, and responding to spoken language. unless turned off and away

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