ABSTRACT

A possible answer for the differences among individuals may be found in the individual capability to use the information available and the capability to associate the information provided with the actual movement performance. Information about ‘how we actually performed’ together and in parallel with information about ‘how we feel about our motor performance’ arrives to the central nervous system (CNS) via different neural paths. Cues about the outcomes of one’s performance may arrive from outside, for example, via visual and/or auditory senses. On the other hand, cues about how one feels about a performance arrive from within the system, via kinaesthetic sensors and, in particular, via proprioceptive afferents. Accordingly, modifications in a movement are done by comparison between what we do (i.e. the actual motor act) and what we should do (i.e. a forward model or a virtual plan of how to perform). Specifically, such comparisons may be carried out by cerebellar structures (Miall et al. 1993). Matching motor plans with actual movements implies a correlation process. Lack of correlation between expected and actual performance is interpreted as a motor error, and thus, the movement should be corrected. In parallel, the plan should be updated via an internal close-loop process (feedback-dependent). Such learning models seem to be supported by neurobiological and neuroanatomical evidence (von Holst and Mittelstaedt 1950). Sperry’s experiments (see Trevarthen 1990, for a review of his work) were among the first to show a functional correlation between neuroanatomy and performance. The behavioral studies of Held (1965) showed adaptation processes that may involve the previously hypothesized neural structures. In those

adaptation experiments, performers received distorted visual input and this was enough to induce passive motor adaptations. Nevertheless, the greatest and sometimes irreversible sensorimotor changes were produced when the performers were active. This has been clearly shown in kittens in a series of classical experiments (Held and Hein 1958, 1963). Proprioceptive information arriving from within is then correlated with the visual input, and this implies an active type of learning and adaptation processes. While vision captures external events (including the outcomes of our own motor actions), proprioception relates to our internal motor experience. The former allows for ‘a posteriori’ corrections of motor errors while the latter enables online corrections during a motor performance. Reliance on vision may induce a dependence on external information, while reliance on proprioception enhances autonomic learning (i.e. independent of external sources of information). It should be mentioned that proprioception is a main sensory channel facilitating feedback. Proprioceptive information arrives via different sensors in the skin, muscles and joints during either static or dynamic conditions of self-motion of body segments or the whole body. The machinery encapsulated within the proprioceptive perception is suited to capture force, velocity, displacement and/or posture (i.e. static configurations of one segment relative to another or relative to the gravity vector). In brief, proprioception allows for sensing a movement (kinesthetic sense) via information about muscle tension, balance and exerted force (i.e. the sense of effort).