Bromage, Adam Carl (2020) Reconceptualising the Nature of Executive Functioning: Introducing the Hierarchical Demand Model (HDM). PhD thesis, Victoria University.

Abstract

Over the past 20 years, many investigations have sought to define the construct of Executive Functioning (EF) via the fragmentation of Executive Function skillsets. This approach has served useful for the demarcation and detailed account of complex cognitive functions that can manifest during various clinical pathologies. Yet, theoretical accounts remain heterogeneous in these representations, and neuropsychological measures of their purported constituents are critiqued for measurement impurity and poor ecological validity. This study aimed to reconceptualise traditional scoring approaches of a variety of EF tests through the lens of cognitive control theory, via a 3-study design. Performance on 13 different EF tests were assessed in 105 participants (Mage= 30.00, SD = 7.11). Study 1 sought to develop, apply, and preliminary test a Demand Classification System (DCS). The DCS comprised of 16 classifications of demand across a criterion of complexity (Abstraction, Contextual Stability, Action Rules, Instruction and Rules, Dual-Task Requirements) and novelty (Automaticity, Schematic, and Episodic). Confirmatory Factor Analysis (CFA) demonstrated that within these tests, performance variance could be attributed to the nature of its internal demands for complexity and novelty. Using congeneric modelling, Study 2 revealed that complexity- novelty classifications accounted for a significant amount of unique shared variance between tests. Factor weighted performance scores were created for each level of demand identified by Studies 1 and 2. Finally, Study 3 aimed to assess the relationships between performance at varying levels of demand using Structural Equation Modelling. The results supported the existence of hierarchically contingent relationships that align with existing neurological mechanisms proposed for cognitive control. The collective outcome of these analyses is the offering of The Hierarchical Demand Model (HDM) which proposes that in order to successfully engage in a goal-directed task the individual must recognise what is known, appraise what is required, and reconcile the difference to formulate an effective response. The HDM and its agent the DCS, collectively serves to operationalise known influencers of demand to the neuropsychological testing environment. This has significant implications not only for the future use of neuropsychological tools as singular measures of EF, but also how these measures can be better utilised for the assessment of overall higher-order cognitive ability. This approach urges the recognition of synergy between cognitive control and EF, and the duality of their influence over the execution of controlled behaviour in response to demand. This project offers not only a methodical system whereby this synergistic approach can be successfully applied, but also a framework that is able to account for the nature of human engagement at various levels of complexity and novelty across a hierarchical continuum of demand.

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