From action representation to action execution: exploring the links between cognitive and biomechanical levels of motor control

Along with superior performance, research indicates that expertise is associated with a number of mediating cognitive adaptations. To this extent, extensive practice is associated with the development of general and task-specific mental representations, which play an important role in the organization and control of action. Recently, new experimental methods have been developed, which allow for investigating the organization and structure of these representations, along with the functional structure of the movement kinematics. In the current article, we present a new approach for examining the overlap between skill representations and motor output. In doing so, we first present an architecture model, which addresses links between biomechanical and cognitive levels of motor control. Next, we review the state of the art in assessing memory structures underlying complex action. Following we present a new spatio-temporal decomposition method for illuminating the functional structure of movement kinematics, and finally, we apply these methods to investigate the overlap between the structure of motor representations in memory and their corresponding kinematic structures. Our aim is to understand the extent to which the output at a kinematic level is governed by representations at a cognitive level of motor control.

Introduction

Research on expertise in sports has shown that skilled performance is based not only on physical ability, but equally on task-specific cognitive competences. During extensive practice, relevant mental representations are formed, adapted, and re-organized in such a way that flawless performance is progressively facilitated, based on increasing order formation in the athlete's long-term memory. According to the perceptual-cognitive perspective, actions are planned and performed on the basis of structured cognitive representations of action effects in motor memory (Hommel et al., 2001; Mechsner et al., 2001; Schack and Mechsner, 2006; Hoffmann et al., 2007; Shin et al., 2010). Furthermore, because these representations govern the tuning of motor commands and muscular activity patterns, skillful coordination occurs when appropriate mental representations of the motor task and action goals are constructed (Schack and Ritter, in press). In order to illustrate how these processes can be conceptualized and explored empirically, we will present studies that investigated the organization of task-related cognitive structures, and the way these structures correspond to functional components of skilled motor performance. Additionally, we will present a new empirical approach for linking these mental structures to the structures observed within the movement kinematics. Before we turn to the methodological aspects of these studies, we will first present the underlying theoretical conceptualization of the cognitive architecture of human motor action, beginning with the concept of mental representations, which is fundamental to this approach.

Mental Representations of Human Motor Action

The idea that cognitive representations play an important role in motor control is reminiscent of classical ideas in psychology, such as the “ideomotor” approach adopted by Lotze (1852) and James (1890) in the 19th century or the model-theory studies of the construction of movement presented by Bernstein (1947) in the middle of the 20th century. James wrote for instance 1890 in his now seminal work The Principles of Psychology: “We may …lay it down for certain that every representation of a movement awakens in some degree the actual movement which is its object” (p. 526). Recently, the term mental representation has been widely used in a large variety of disciplines, often with rather diverse content. Gilbert and Wilson (2007) have stated: “the mental representation of a past event is a memory, the mental representation of a present event is a perception, and the mental representation of a future event is a plan.” Even though this definition sounds viable, it might not be sufficient for our purposes. Mental representations were first discussed in the philosophy of language, referring mainly to linguistic representations. Later, the issue was adapted by other disciplines such as philosophy of mind and psychology, and various theories have been formulated to describe the nature of mental representations. From these theoretical perspectives, the functionalistic one seems most relevant in our context, as it states that mental representations predominantly play a functional role for the cognitive system. According to this perspective, the function of mental representations is to make situations and objects cognitively available that are otherwise physically unavailable—in this respect, they are the only way to make non-actual situations and objects available for thinking and acting (Vosgerau, 2009).

Several authors have reflected upon the nature of mental representations of actions (e.g., Rosenbaum et al., 2001), and it has been argued that even mental representations of static objects are dynamic in nature, as they are derived from and based on dynamical action representations, which are evolutionarily more relevant for controlling behavior than representations of static scenes or objects (Freyd, 1987). In the context of the studies presented in the following, we refer to mental representations in terms of states of mind that correspond to experiences, and to the physical reality of objects and movements. Such internal representations arise from exposure to sensory stimuli, are multimodal, and refer to objects or events that we perceive in our environment via the processes of perception and processing in our brain (Barsalou, 2008). Mental representations occur on different levels and, due to the nature of our nervous system, can be independent of the actual presence of the object that they refer to in the world. Our ability to store such representations is the basis of our ability not only to learn, but also to make plans and predictions regarding what will happen in the future. Wilson (2002) points out that our cognitive apparatus can even construct mental representations of situations that we have never experienced, purely on the basis of linguistic input. Mental representations thereby play a central role in the control and organization of actions, serving as “organizers of activity” (Steels, 2003). In cognitive systems, internal representations co-evolve together with corresponding actions and become vehicles for higher mental functions, such as thinking and planning (Steels, 2003). As a consequence, these representations stay closely connected to the actions they serve (Glenberg, 1997), resembling them most crucially in terms of structural similarity (Johnson-Laird, 1989). Mental representations are considered vital for learning complex movements and movement sequences, for refining and adapting learned movements to the requirements of actual situations, and for automatizing movement patterns on an expert level. Expert performance in sports is typically characterized by a high degree of control and a sense of clarity, which can arise based on regularities in the mental representation that allow for relieving cognitive load, or, as Wilson (2002) has put it, for circumventing the “representational bottle neck.”

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