Mediators of Decision Making in Action Planning: Assessing the Functional Costs of Alternative Movement Strategies

Abstract

The human motor system is constantly faced with decisions about how to choose a path when navigating our environment. These types of decisions occur rapidly and constantly, from initial movement planning, through movement execution, to completion. With infinite ways to complete any given task, the central nervous system generally, and motor control systems specifically, must somehow “decide” the best way to do this while taking into account physiological and environmental constraints. In addition, these movement choices must consider the feasibility and efficiency of all movement alternatives. For example, when deciding between paths that vary in reach distance and walking distance, the path with the shorter reach distance is more likely to be chosen, as reaching is deemed to be ~10x more costly than walking a given distance (Rosenbaum et al., 2011; Rosenbaum, 2012). It is not clear, however, how much more costly the non-chosen path is, compared to the chosen path, and what factors are mediating these decisions. Thus, the purpose of this thesis was to investigate potential underlying non-cognitive mediators of behavioural decisions involved with posture selection during tasks that occur within a constrained task environment, by quantifying the biomechanical mechanisms that may be driving these decisions. Chapter 2 replicated and extended upon the work of Rosenbaum et al. (2011) by recording whole-body motion capture during a bucket transfer task. This study was the first to look at the loading of the shoulder joint and trunk during the reaching and walking decision paradigm, comparing joint loading in the chosen versus unchosen paths. In Chapter 3, participants made decisions between movements with seemingly similar functional distances, in a four-choice reaching and walking paradigm. Behavioural outcomes suggest that the decision-making process reflects spatial coding of the movement goal that is backwards planned from the task sub-goal. Chapter 4 explored how perceived costs of multiple task variables are prioritized and integrated into action planning. Here, participants prioritized decreased reach distance over bearing an increased load. Collectively, this thesis provides evidence that bottom-up processes, namely the biomechanics of the shoulder and trunk, exert influence on cognitive decision-making and action planning, as reflected in decreased joint loading in chosen versus unchosen paths.