What is the difference between an auditory processing disorder and a language processing disorder?
The word "processing" has caused much debate and uncertainty among audiologists, speech-language pathologists, psychologists, teachers, and parents. Labels such as language processing, central auditory processing, auditory processing, phonological processing, temporal processing, and auditory perception and comprehension are used to name what humans do when they receive, perceive, interpret, and understand language, or when they fail to do one or more of these aspects in the acquisition and use of language. Various definitions have been proposed for each of these terms. For example, several definitions are available in the literature on central auditory processing and its disorders. ASHA published definitions in 1990 and in 1996 that provide extensive information on the complexity of these heterogeneous processes and deficits. The 1990 definition includes a description of the behavioral correlates involved in processing that ultimately correspond to the neuroanatomical processes involved in processing linguistic and non-linguistic acoustic information.
Central auditory processing disorders are deficits in the formation of processing of audible signals not attributed to impaired hearing, sensitivity or intellectual impairment. Specifically, CAPD refers to limitations in the ongoing transmission, analysis, organization, transformational, elaboration, storage, retrieval, and use of information contained in audible signals. This processing involves perceptual, cognitive, and linguistic functions which, with appropriate interaction, results in effective receptive communication of passive (e.g., conscious and unconscious, mediated and unmediated) ability to: attend, discriminate, and identify acoustic signals; transform and continuously transmit information through both the peripheral and central nervous systems; filter, sort and combine information at appropriate perceptual and conceptual levels; store and retrieve information efficiently; restore, using phonological, semantic, syntactic, and pragmatic knowledge; and attach meaning to a stream of acoustic signals through utilization of linguistic and non-linguistic contexts (ASHA, 1990, pp. 13).1
Another definition of CAPD proposed by the Task Force on Central Auditory Processing Consensus Development (ASHA, 1996) also focuses on the behavioral characteristics of the disorder.
Central Auditory Processes are the auditory system mechanisms and processes responsible for the following behavioral phenomena:
- Sound localization and lateralization
- Auditory discrimination
- Auditory pattern recognition
- Temporal aspects of audition, including temporal resolution, temporal masking, temporal integration, temporal ordering
- Auditory performance decrements with competing acoustic signals
- Auditory performance decrements with degraded acoustic signals 2
Many neurocognitive mechanisms and processes are engaged in recognition and discrimination tasks. Some are specifically dedicated to acoustic signals, whereas others (e.g., attentional processes, long-term language representations) are not. With respect to these nondedicated mechanisms and processes, the term central auditory processes refers particularly to their deployment in the service of acoustic signal processing (1996).
This second definition not only specifies the auditory aspects of processing, but it also makes a distinction regarding processing that is not dependent on acoustic signals. This distinction leads to a broader discussion of language processing. Consider the other modes we use to receive, perceive, analyze, store, retrieve, formulate and produce language. For example, we can use sign language to transmit and to comprehend messages. Individuals, who are deaf or hard of hearing, process language without the benefit of an intact auditory system. We "read" paralinguistic cues (facial expressions, body posture, gestures) as we communicate with others and know that such cues sometimes support, but other times do not support the verbal message that we hear. Written language is another way that we process language without direct auditory input. Reading and writing development is certainly facilitated by knowledge of verbal speech and language, but development is possible without verbal input. These examples show that language processing exists in tandem with auditory processing, but also independent from it.
In the 1980s researchers and theorists debated bottom-up information processing and top-down information processing explanations for language learning. The bottom-up theories emphasize accurate reception and perceptual processing of sensory information prior to its higher level analysis and construction of meaning. Top-down models of language processing emphasize the influence of higher order thinking (whole-to-part) over perceptual analysis. Schemes are learned through experiences and are used to make predictions about sensory information. Interactive theories of information processing combine the views of bottom-up and top-down processing theories that occur through parallel processing and add the active participation of the learner and the clarity of the linguistic and nonlinguistic information as important characteristics (Nelson, 1998).
Speech-language pathologists and audiologists are called upon by parents, teachers and others to investigate the nature of processing problems in students. It is necessary to obtain thorough case histories so that a complete picture of students' strengths and needs are revealed. Attention problems, language disorders, learning disabilities, hearing loss and even second language learning can appear to some as characteristic of "processing disorders." The goal of assessment should be to rule out these related problems or to document their existence and to then describe the nature and extent of processing problems and whether such problems are specific to language or more broadly associated with non-linguistic and linguistic information. The audiologist, speech-language pathologist and psychologist should work collaboratively to arrive at the diagnosis. The presence of a central auditory processing problem requires specific goals and strategies in classroom management, instructional modifications, intervention, and amplification. If a general or specific language processing problem exists, goals and strategies should focus on instructional modifications, interventions specific to the areas of language that require improvement, and classroom management.
1Source: "Audiological assessment of central auditory processing: An annotated bibliography" by American Speech-Language-Hearing Association, 1990, Asha, 32(Suppl.1),pp. 13-30. Copyright 1990 by American Speech-Language-Hearing-Association.
2Source: "Central auditory processing: Current status of research and implications for clinical practice" by American Speech-Language-Hearing Association, 1996, American Journal of Audiology, 5(2), pp. 41-54. Copyright1996 by American Speech-Language-Hearing Association.
Kathleen Fahey, Ph.D., CCC-SLP is a professor and the chair of the Department of Communication Disorders at the University of Northern Colorado. She is the author of the text ''Language Development, Differences, and Disorders: A Perspective for General and Special Education Teachers and Classroom-Based Speech-Language Pathologists, as well as many articles and presentations. Kathleen teaches undergraduate and graduate courses in phonology and language.