Wilson, W.J. (2018). On the definition of APD and the need for a conceptual model of terminology. International Journal of Audiology, Early online. doi: 10.1080/14992027.2019.1600057 This is a copy of the final, accepted manuscript prior to copy editing by the journal’s editorial staff. The published version of this manuscript is available at: https://www.tandfonline.com/eprint/GPziH3cPSmb7KXt6u6En/full?target=10.1080/1499 2027.2019.1600057 On the definition of APD and the need for a conceptual model of terminology Wayne J Wilson Corresponding author: Wayne Wilson, School of Health and Rehabilitation Sciences, The University of Queensland 4072, Australia, [email protected] Objective: To consider the definition of auditory processing disorder (APD). Design: Narrative review and opinion piece. Study sample: Considerations of definition drawn primarily from the fields of philosophy, audition, learning and language. Results: The problem of defining APD appears genuine. Current and previous definitions of APD are nominal in nature, being both stipulative (offering explicit and arbitrary adoptions of meaning relation between words) and operational (creating rules that stipulate how the terms might apply to particular cases). Such definitions survive by consensus and perceived heuristic value in a manner that fails to achieve closure as arguments about their validity remain relative. Conclusion: A conceptual model of APD terminology is needed that considers nominal, conceptual and real definitions as well as different purposes for defining APD within professional and public domains. A framework for such a conceptual model of APD terminology is offered. This paper considers the definition of auditory processing disorder (APD). Types of definition are considered and applied to the definition of APD offered by the American Speech‐language, Hearing Association (ASHA, 2005) and the American Academy of Audiology (AAA, 2010). The discussion is then expanded to more broadly consider seven questions about terminology that identify dilemmas of defining APD, the limited prospects of finding a unifying definition of APD, and the resulting need for a conceptual model of terminology for APD. The paper concludes by proposing a framework for such a model that considers both different types of definition and different purposes for defining APD within professional and public domains. Further development of a conceptual model of terminology for APD could improve communication amongst all stakeholders seeking to help children who present with listening difficulties in the classroom. Many of the arguments offered in this paper draw directly from Kavale and Forness’s (2000) consideration of definitions of learning disabilities, Bishop’s (2014) consideration of terminology in developmental language disorders, and Walsh’s (2005) consideration of a conceptual model of terminology for speech pathology. Background Even a cursory view of the research and popular literature identifies many definitions of “auditory processing disorder (APD)”. Recent definitions have split into two broad camps (Wilson, 2018). The first seeks to maintain the use of APD as a diagnostic label for deficits in the neural processing of auditory stimuli particularly in the central auditory nervous system (CANS) that are not due to higher order language, cognitive, or related factors (e.g., ASHA, 2005; Nickisch et al., 2007, AAA, 2010; CISG, 2012; Keith et al., Forthcoming). The second seeks to redefine APD or to replace it with a new term that better reflects an argument that listening difficulties more broadly are predominantly the result of deficits in neural processing of auditory stimuli due to higher order language, cognitive, or related factors (Moore et al., 2010; de Wit et al., 2016; de Wit et al., 2017). The ongoing failure to produce a unified definition has contributed to APD lacking two critical scientific elements: understanding via a clear and unobscured sense of APD (an account of the essence of APD), and explanation via a rational exposition of the reasons why a particular child has APD (an account of the properties of APD; a demonstration of APD). Without understanding and explanation, statements about APD remain conditional in a manner that worsens rather than improves our ability to reach consensus on its definition. Types of definition (after Kavale & Forness, 2000) A definition is a semantic device that uses words for descriptive purposes to convey not just factual information but also meaning (Kavale et al., 1991; Kavale & Forness, 2000). Creating a definition is challenged by the need translate fundamental and basic qualities into words that are open to interpretation (Miller, 1980). Definitions are integral for developing taxonomies (Broadfield, 1946; Kavale & Forness, 2000) by an epistemic process of naming, distinguishing, and ordering of types (Reichenbach, 1938; Kavale & Forness, 2000). This process seeks to identify subgroups in a population (naming), decide if a particular case fits (distinguishing), and establish the degree of fit according to the available corpus of knowledge (ordering) (Korner, 1970; Kavale & Forness, 2000). Valid and reliable taxonomies rely on definitions that comprehensively describe what is being classified. Definitions can be broken down into many different types (Robinson, 1954; Kavale & Forness, 2000) of which five will be considered for the purposes of the present review: real, conceptual, nominal, stipulative and operational. Real definitions are hypothesized ideals that are not often achieved as they are concerned with the properties of things in the world (Fetzer, 1991) in a manner that seeks to “account for the essence of a thing” (Aristotle, cited in Robinson, 1954). Conceptual definitions represent sets of characteristics drawn from concepts that have been theoretically validated (as opposed to characteristics drawn only from things that have been measured) (Hempel, 1952; Kavale & Forness, 2000). Nominal definitions are concerned with words as elements of language (Fetzer, 1991) in a manner that attempts to associate words to describe something (Kavale & Forness, 2000). Nominal definitons can be further broken down into stipulative and operational definitions (Kavale & Forness, 2000). Stipulative definitions are explicit and arbitrary adoptions of a meaning relation between words that serve as requests that readers or listeners will understand words in a certain way (this makes stipulative definitions useful but does not necessarily prove them to be true) (Rantala, 1977). Operational definitions are sets of rules that describe how terms apply to particular cases (Benjamin, 1955). It might be useful to note that colloquial statements used in some western countries such as something being “true by definition” and “for the purpose of argument X, Y will be defined as …” can be seen as nominal. Applying the types of definition described above to defining APD suggests a real definition of APD would be one that comprehensively accounts for the essence of the thing that is APD. A conceptual definition of APD would describe the set of characteristics that define APD with each characteristic drawn from a theoretically validated concept. A nominal definition of APD would associate words to describe APD. Its stipulative component would offer explicit and arbitrary meaning relations between the words in the definition in a manner that is useful but does not necessarily prove those relations to be true, and its operational component would outline the rules for applying the words and their relations in the definition to determine if an individual person fits the nominal definition of APD. A definition of APD: ASHA (2005) and AAA (2010) Perhaps the most cited definition of APD in recent times is that offered by ASHA (2005) and AAA (2010). This definition proceeds in three parts. The first broadly defines auditory processing (AP) as referring to the efficiency and effectiveness by which the CNS utilizes auditory information. The second narrowly defines AP as referring to the perceptual processing of auditory information in the CNS and the neurobiologic activity that underlies that processing and gives rise to electrophysiologic auditory potentials; and includes the auditory mechanisms that underlie the following abilities or skills: sound localization and lateralization, auditory discrimination, auditory pattern recognition, temporal aspects of audition, auditory performance in competing acoustic signals, and auditory performance with degraded acoustic signals. The third defines APD as referring to difficulties in the perceptual processing of auditory information in the CNS as demonstrated by poor performance in one or more of the AP skills previously listed, that is not due to higher order cognitive‐ communicative and/or language related functions. A consideration of the definition of APD offered by ASHA (2005) and AAA (2010) shows it is not real as it does not achieve a hypothesized ideal that comprehensively accounts for the essence of the thing that is APD. Nor is it completely conceptual as while it represents a set of characteristics drawn from concepts regarding APD, some of those concepts are still undergoing theoretical validation (an example here being the concept of dichotic listening as being auditory, cognitive, or both; with Cameron et al’s (2016) use of the Dichotic Digits difference Test being an example of efforts to progress the theoretical validation of the concept of dichotic listening). Instead, the definition