ABSTRACT
An action is willed when we consciously pay attention to its selection (James 1890). Such a deliberate selection is subjectively experienced as willed and occurs when we have a choice of action. Spontaneous or self-generated actions are not specified by an external trigger stimulus, but are internally driven. They may be contrasted with automatic acts where the appropriate response is fully specified by an external stimulus (Norman & Shallice 1985). Goldberg (1985) and Passingham et al. (1989) have proposed that internally driven and stimulus driven responses are associated with different brain systems. For example, lesions in the supplementary motor area (sma) impair internally generated responses, but not those elicited by external stimuli (Passingham et al. 1989). Goldman-Rakic (1987) proposed that, for monkeys to succeed in the delayed performance test, an area of dorsolateral prefrontal cortex (the monkey equivalent of Brodmann area 46) is required to be intact. In this test the response is not sufficiently specified by the currently available stimulus and has to be determined by a representation held in memory. Shallice (1988) suggested that the frontal cortex in man subserves a ‘supervisory attentional system’ (sas) that is critically needed for the performance of novel tasks, but not for the performance of routine tasks in which actions are specified by the current situation. In novel situations, the sas takes over control of action by using routine stimulus analysis and response production mechanisms in novel combinations.
