Human beings possess the capacity to move intentionally, i.e. to move in such a way that intended outcomes are achieved. For example, a person intending to pick up a pen lying in front of him, will move his body, arm and hand in a gesture that accurately and effortlessly leads to the desired result. People are sometimes aware of their intentions and capable of expressing them verbally. However, they are largely unaware of the processes taking place in their nervous systems that transform their intentions into actions. In music making, the production of intended musical outcomes is the goal of the activity. Musical intentions and corresponding auditory expectations of outcomes of musical actions are the primary agent of motor control processes. Put differently, based on anticipations of intended musical sounds, the nervous system generates patterns of movement that lead to the production of the former. Novembre and Keller explain this fundamental insight by means of the following example:
Let us take a basic example: striking a piano key with a finger. The movement (striking the key) is intended to generate a goal (a piano tone). When this is observed from the “outside” perspective of another individual, this phenomenon seems straightforward: the movement preceded its goal. However, when considering a “first person” perspective, it is the musician’s intention (i.e., producing a piano tone) that leads the generation of a movement: moving the finger toward the piano key. This distinction might seem trivial, but in fact it represents a fundamental step to understanding that movements and their ensuing effects are intrinsically coupled in the human brain and in cognition. More specifically, a representation of a perceptual effect can trigger the movement necessary to produce the effect itself (Novembre and Keller, 1).
Before initiating a goal-directed action, the individual must have a representation of the desired effect in mind and must use this representation to select a movement pattern that will successfully bring about this effect. This insight was first described by the philosopher William James and has become known as the “ideomotor principle” (James 1890).Recent neuroscientific research has suggested that the nervous system achieves this transformation of intention into accurate motor control by means of predicting the sensory consequences of one’s actions, a phenomenon known as predictive processing (Adams, Shipp and Friston 2013). Based on the intended outcome of the action, the brain continuously predicts the required movements and the sensations that will arise as a result of them. These predictions are based on previous experiences and implicit knowledge of our own body and the world around us. Implicit knowledge here refers to the individual not being aware of having learned it and not being capable of expressing it verbally, but demonstrating the knowledge indirectly via performance (Willingham, et al. 2000), otherwise known as tacit knowledge. Put simply, the brain “knows” how to affect the surroundings in order to achieve intended results, and which actions of the body are required, as a result of prior experiences. Preceding the initiation of actions and during their performance, the brain keeps readjusting its predictions, thus enabling accuracy and early processing of feedback that results from one’s actions. The feedback that results from such actions can be divided into exteroception, by which one perceives the outside world, and proprioception, which is the sense of the relative position of one's ownparts of the bodyand strength of effort being employed in movement (Anderson and Glanze 1994). Muscles, tendons and joint capsules are equipped with sensors that continuously keep the nervous system updated on muscle effort, the force exerted on tendons, joint position and speed of movement. Adams et al. have argued that the signals the brain sends down the spine in order to generate intended actions should be seen as predictions of the proprioceptive onsequenses of these actions. Classical reflex arcs at the levelof the spine, respond to these predictions by fulfilling them: they bring about changes in muscle length and joint position so that the actual proprioceptive signals match the predictions, thus producing the intended movements (Adams, Shipp and Friston 2013).
The effects of predictive processing can be seen in certain aspects of motor control in musicians. For instance, pianists have been found to perform wrong keypresses (“wrong notes”) softer than correct keypresses. In conjunction with this, differences in brain activity connected to wrong or correct keypresses are observable already 100 milliseconds before keypresses are fully executed (Maidhof, et al. 2009). In practical terms, this indicates that pianists “know” they are going to play a wrong note a split second before playing it and even (non-consciously) try to mitigate negative consequences of the wrong note by playing it softer. This phenomenon is attributed to predictive processing in the pianist’s brain, more specifically the detection of a mismatch between a predicted sensory consequence of an action and the intended action goal.