Blakemore, Wolpert and Frith (2002) propose a framework of motor (or action) control and describe several disorders which appear to support this framework, including optic ataxia, utilization behaviour and phantom limbs.
Central to this framework are two internal models of the central nervous system. The ‘inverse model’ works on the basis of goal perception and the initiation of any action or sequence of events that are necessary in order to achieve that goal. Blakemore et al.(2002) offer the example of picking up a cup – affordances in the form of the visual features of the cup (the shape and angle of the handle for example) will guide how you position your hand in order to grasp it and pick it up. However, whilst perception and awareness of the cup are conscious, the details of each step in the process of reaching out and picking up the cup are outside of awareness.
Whilst the ‘inverse model’ appears to employ goal perception to shape a plan of action, the ‘forward model’ operates on the basis of prediction of the consequences of action by using efference copy. Whenever a movement is made, the brain simultaneously generates a mental ‘copy’ of that movement or motor command from which a prediction can then be made about the effect of that action. Importantly, comparisons between the predicted and desired outcome of an action as well as between the predicted and actual sensory feedback are made. Although the results of these comparisons appear to take place outside of conscious awareness (if the intended action is achieved), it is suggested that the ‘forward model’ has the effect of determining not only our subjective experience, but also our awareness of action control.
Reference: Blakemore, S., Wolpert, D. M. & Frith, C. D. (2002). Abnormalities in the awareness of action. Trends in Cognitive Sciences, 6, 237-242
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